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Clinical Microbiology Reviews, October 2002, p. 716-746, Vol. 15, No. 4
0893-8512/02/$04.00+0     DOI: 10.1128/CMR.15.4.716-746.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Clinical and Taxonomic Status of Pathogenic Nonpigmented or Late-Pigmenting Rapidly Growing Mycobacteria

University of Texas Health Center, Department of Microbiology, Tyler, Texas

SUMMARY

INTRODUCTION

EPIDEMIOLOGY

TAXONOMY AND CLINICAL SIGNIFICANCE

M. fortuitum Group

Historical perspective.

(i) M. fortuitum.

(ii) M. peregrinum.

(iii) M. fortuitum third biovariant complex.

(iv) M. mucogenicum.

(v) M. senegalense.

Type of disease.

(i) Community-acquired disease.

(ii) Health care-associated disease.

Geography.

Individual taxa.

(i) M. fortuitum.

(ii) Unnamed third biovariant complex including M. septicum, M. mageritense, M. houstonense (proposed), and M. bonickei (proposed).

(iii) M. peregrinum.

(iv) M. mucogenicum.

(v) M. senegalense.

(vi) M. septicum.

M. chelonae-abscessus Group

Historical perspective.

Type of disease.

(i) Community-acquired disease.

(ii) Health care-associated disease.

Geography.

Individual taxa.

(i) M. chelonae.

(ii) M. abscessus.

(iii) M. immunogenum.

M. smegmatis Group

Historical perspective.

Type of disease.

(i) Community-acquired disease.

(ii) Health care-associated disease.

Geography.

Individual taxa.

(i) M. smegmatis sensu stricto.

(ii) M. goodii.

(iii) M. wolinskyi.

Other nonpigmented RGM of uncertain clinical (human) significance.

TREATMENT OF INFECTION

Antimicrobial Treatment

General.

M. fortuitum group.

M. chelonae-abscessus group.

M. smegmatis group.

Newer drugs.

Duration of therapy.

Surgical Treatment

CLINICAL FEATURES OF INFECTIONS

Posttraumatic Wound Infections

Bone and Joint Infection

Postsurgical Wound Infections

Postinjection Abscesses

Catheter-Related Infections

Disseminated Cutaneous Disease

Pulmonary Disease

Central Nervous System Disease

Miscellaneous Diseases

Otitis media.

Corneal infections (keratitis).

Cervical lymphadenitis.

LABORATORY ASPECTS OF THE RAPIDLY GROWING MYCOBACTERIA

General

Biochemical and Phenotypic Identification

High-Performance Liquid Chromatography

Molecular Identification

Nucleic acid probes.

PCR-restriction enzyme analysis.

Plasmid profiles.

Ribotyping.

Hybridization.

Direct detection in paraffin-embedded tissue.

Fluorescence in situ hybridization assay.

Susceptibility Testing for Taxonomic Purposes

Susceptibility Testing for Clinical Purposes

Agar disk diffusion.

Agar disk elution.

E test.

Broth microdilution MIC.

CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

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INTRODUCTION

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The species of rapidly growing mycobacteria (RGM) capable of producing disease in humans consist primarily of the Mycobacterium fortuitum group, the M. chelonae/abscessus group, and the M. smegmatis group. Key features for identification of these groups are the presence of typical long-chain fatty acids known as mycolic acids, growth of readily visible colonies on primary isolation within 7 days on multiple types of solid media, arylsulfatase activity within 3 days or 2 weeks, and the absence or slow appearance of any pigmentation (144).

Historically, the M. fortuitum group has been composed of two known species and a taxon which has been reported to include more than one species (82). The species include M. fortuitum (formerly M. fortuitum biovar fortuitum), M. peregrinum (formerly M. fortuitum biovar peregrinum) and the taxon known as the unnamed third biovariant complex (96). Several additional taxa to be discussed later are candidates for inclusion in this group.

M. chelonae (formerly M. chelonae subsp. chelonae) and M. abscessus (formerly M. chelonae subsp. abscessus) (89), along with the newly recognized species M. immunogenum (212), are members of a group known collectively as the M. chelonae-abscessus group.

Finally, the M. smegmatis group contains M. smegmatis sensu stricto and two newly described species: M. goodii, and M. wolinskyi (17, 199).

Prior to recent molecular reevaluations, the taxa in the M. chelonae-abscessus and the M. fortuitum group were considered "subspecies" or "biovariants," respectively. However, the introduction and evolution of 16S ribosomal gene (rDNA) sequencing provided strong evidence that these biovars and subspecies were in fact separate species. Gene sequencing also permitted much easier recognition of new taxa, since investigators could use data banks for strain comparisons rather than performing the much more technically difficult genomic DNA-DNA pairing experiments with all potentially related taxa. The genomic DNA-DNA pairing experiments that show <70% homology to other species still remain the "gold standard" for recognition of new species, but such studies are performed infrequently and many new species of mycobacteria are based genetically on 16S rDNA comparisons only.

In this review, we update the taxonomy of these nonpigmented RGM and point out many of the changes brought about by such newer technologies as 16S rRNA gene sequencing; high-performance liquid chromatography (HPLC) of mycolic acid esters, including fluorescence-HPLC; and PCR restriction fragment length polymorphism (RFLP) analysis (PRA) of a 439-bp fragment (referred to as the Telenti fragment) of the 65-kDa heat shock protein-encoding gene (hsp65) (174). Clinical disease caused by these groups, together with their drug susceptibility, and most effective drug treatment are also addressed. The disease syndromes caused by these organisms are listed in Table 1.

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These hardy species of RGM are commonly seen in municipal tap water (31). One study by Carson et al. (31) showed that 55% of the incoming city water in hemodialysis centers throughout the United States contained RGM. Some outbreaks of human infection related to these organisms have involved hospital water systems as the microbial reservoirs. Recently, the presence of acid-fast mycobacteria in up to 90% of biofilms (the slime layer present at water-solid interfaces) taken from piped water systems has been described (153). The presence of acid-fast mycobacteria in these biofilms probably serves as a major environmental reservoir for organisms such as M. kansasii, M. mucogenicum, M. simiae, M. xenopi, and M. gordonae.

Because of the ubiquity of the RGM, human infections have been reported from most geographic areas in the world (213) and species of RGM have been recovered from 30 to 78% of soil samples throughout the United States (117). Most nosocomial (hereafter referred to as health care-associated) outbreaks and pseudo-outbreaks have occurred in the United States and seem to be concentrated mainly in the South. M. senegalense, originally found in Africa, has never been described elsewhere. Such a localized distribution among the RGM seems to be rare, however.

Health care-associated outbreaks and pseudo-outbreaks commonly involve exposure to tap water or water sources such as ice, ice water, and water-based solutions (29, 39, 80, 146, 189, 198). Contaminated ice machines are a relatively important hospital reservoir for the RGM, especially M. fortuitum. Reported disease outbreaks have included sternal wound infections (189, 198), surgical wound infections following plastic surgery (192, 194), and postinjection abscesses (57, 183). Catheter infections also have been associated with the RGM, including M. mucogenicum (189, 200, 205). Pseudo-outbreaks of disease, defined as clusters of false infections or artifactual clustering of real infections, have been associated with contaminated bronchoscopes and automated endoscopic cleaning machines with tap water as the source of the organism (54, 55).

Localized infection in sporadic community-acquired disease usually occurs after a traumatic injury followed by potential soil or water contamination (9, 203, 205). Such injuries as stepping on a nail, motor vehicle accidents, compound fractures, etc., are typical of the clinical histories seen in patients with RGM disease (203, 205).

TAXONOMY AND CLINICAL SIGNIFICANCE

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Historical perspective. (i) M. fortuitum. M. fortuitum was the designation given by da Costa Cruz (42) to a strain of RGM (ATCC 6841^T) isolated from a human postinjection abscess in 1938. Subsequently, Stanford and Gunthorpe (162) determined that the isolate was identical to an established species known as M. ranae, with the type strain isolated from a frog by Küster in 1905 (88). Runyon (144) challenged the name M. ranae, in part because many isolates identified as M. ranae were subsequently found to be M. smegmatis and in part because the name M. fortuitum was more widely recognized and established in the medical literature. Hence, in 1972, the Judicial Commission of the International Committee of Systematic Bacteriology of the International Association of Microbiological Societies ruled in favor of Runyon's recommendation to maintain the species designation M. fortuitum, which has remained to the present (144).

(ii) M. peregrinum. M. peregrinum was first proposed in 1962 when Bojalil and colleagues published the first Adansonian or numerical classification of mycobacteria (10, 11). This analysis separated mycobacteria into 12 different categories or branches based on physiological characteristics. Branch 1 consisted of M. smegmatis, M. phlei, and a group of other strains that showed the greatest metabolic capacity of all the strains analyzed. The name M. peregrinum sp. nov. was proposed for this latter group (Latin adjective meaning strange or foreign) because "they were the only non-pigmented strains in Branch 1" (10, 11). The type strain is ATCC 14467^T.

(iii) M. fortuitum third biovariant complex. In 1966 Bönicke divided isolates of the M. fortuitum group into three subgroups on the basis of differences in acid production from carbohydrates and designated them biotypes A, B, and C (13). Biotype A had no unique carbohydrates, biotype B was mannitol positive, while biotype C was mannitol and inositol positive. Subsequently, Pattyn et al. (124) renamed these three Bönicke biotypes M. fortuitum biovariant fortuitum, M. fortuitum biovariant peregrinum, and an unnamed third biovariant.

In 1984, Tsang et al. (176) used a combination of chemical analysis, seroagglutination, and enzyme-linked immunosorbent assay to compare the glycolipids of the RGM and provided evidence that M. fortuitum biovar peregrinum was a separate species (176). M. fortuitum biovar peregrinum was later confirmed as an independent species, as M. peregrinum, based on genomic DNA-DNA relatedness studies by Levy-Frébault et al. (96) and Kusonoki and Ezaki (89) that showed <70% genomic DNA-DNA homology of M. peregrinum (ATCC 14467^T) to other RGM species. By 16S rDNA sequencing, M. peregrinum (ATCC 14467^T) is unique, with a Hamming distance of 9 to 15 bp from other members of the M. fortuitum group. Wallace et al. noted two subgroups within M. peregrinum. One group contained the ATCC type strain (ATCC 14467^T), which was pipemidic acid susceptible; while the other, represented by ATCC 35755, was pipemidic acid resistant. The two groups have different PRA patterns with the hsp65 gene (165). An analysis of the taxonomic status of this second group using phenotypic and genetic analysis is ongoing (M. F. Schinsky, R. E. Morey, M. P. Douglas, A. G. Steigerwalt, R. W. Wilson, M. M. Floyd, M. I. Daneshvar, B. A. Brown-Elliott, R. J. Wallace, Jr., M. M. McNeil, D. J. Brenner, and J. M. Brown, unpublished).

M. fortuitum biovar fortuitum was also elevated to species status (M. fortuitum) based on DNA-DNA pairing studies which showed <70% homology of M. fortuitum ATCC 6841^T to other taxa (89,96). By 16S rDNA sequencing, M. fortuitum differs by only 6 bp from the unnamed third biovariant sorbitol-negative group, by 8 bp from M. senegalense, and by 15 bp from M. peregrinum (ATCC 14467^T).

The unnamed third biovariant, first described by Bönicke in 1966 (13), was later characterized and then subdivided into two groups by Wallace et al. (194) on the basis of a number of characteristics including sorbitol utilization. The two unnamed third biovariant groups were known as M. fortuitum third biovariant, sorbitol positive, and M. fortuitum third biovariant, sorbitol negative (194). By 16S rDNA sequencing, these two groups had a Hamming distance of 9 (160), with proposed representative strains being ATCC 49403 (sorbitol positive) and ATCC 49404 (sorbitol negative) (194). They differed by up to 20 bp from other M. fortuitum group members. Both sorbitol-positive and negative groups appeared heterogeneous, especially when studied for ß-lactamase alleles (225) but also when compared by PRA of the hsp65 gene (165).

(a) M. houstonense and M. bonickeii (proposed species). Investigations currently under way may better delineate the multiple taxa or species within the third biovariant complex. Currently, at least six new species have been delineated. The majority of the sorbitol-positive group have been renamed M. houstonense, while the majority of the sorbitol-negative group have been renamed M. bonickei (Schinsky et al., Abstr. 12th Int. Symp. Biol. Actino.). Additional details of these species await publication of the entire study.

(b) M. septicum.M. septicum is one of the new species within the third biovariant complex. The type strain (ATCC 700731^T) was the causative agent of central- line sepsis in a child with metastatic hepatoblastoma (74, 152). By HPLC analysis of mycolic acids, the isolate was distinctive but closely related to other members of the M. fortuitum group (156, 194), including M. senegalense. Standard biochemical testing showed the isolate to be similar to members of the unnamed third biovariant complex sorbitol-negative group (i.e., mannitol positive, inositol positive, sorbitol negative). Although initial testing showed the isolate to be arylsulfatase negative, it has been found to be positive in other laboratories (K. Jost, unpublished data). Analysis of the 16S rDNA showed a sequence related to but not identical to M. fortuitum, M. peregrinum, and M. senegalense (Schinsky et al., Abstr. 12th Int. Symp. Biol. Actino.).

(c) M. mageritense.The first five reported organisms in the new species M. mageritense were isolated from human sputa in two hospitals in Spain but were not considered clinically significant (46). Recently, six clinical isolates of this species were recovered in the United States, four of which were associated with clinical disease (190). Phenotypically, by antibiotic susceptibility patterns and biochemical tests, isolates of M. mageritense resemble sorbitol-positive members of the M. fortuitum third biovariant complex (positive for mannitol, inositol, and sorbitol) (190). By sequencing of its 16S rDNA, however, genetically, M. mageritense is more closely aligned with members of the M. smegmatis group (17). M. mageritense differs by only 9 bp from the type strain of M. wolinskyi (ATCC 700010^T), by 16 bp from the type strain of M. goodii (ATCC 700504^T), and by 18 bp from the type strain of M. smegmatis sensu stricto (ATCC 19420^T). It generally differs by 23 to 28 bp from members of the M. fortuitum group. Future phenotypic and molecular studies of M. mageritense that include larger numbers of isolates may provide a more complete and accurate taxonomic placement of this species.

(iv) M. mucogenicum. M. mucogenicum has been recognized as a species since 1995. The organism was first called M. chelonae-like organism (MCLO) in 1982, when it was reported as the etiologic agent in a peritonitis outbreak involving two peritoneal dialysis units (5). It was given the designation MCLO because the outbreak strain, just as M. chelonae, was nitrate negative and growth was inhibited on 5% NaCl. In 1993, a large number of sporadic clinical isolates were evaluated by Wallace and colleagues (200) by using biochemical reactions, HPLC of mycolic esters, and antibiotic susceptibility patterns. Subsequently, in 1995, Springer et al. proposed the name M. mucogenicum for this organism group, reflecting the highly mucoid character of the isolates (160). This species has always been grouped with the M. chelonae-abscessus group, but is unlike that group in that approximately 50% of isolates are nitrate positive, have a weak but positive iron uptake, and are much more susceptible to antibiotics including the fluoroquinolones, amoxicillin-clavulanic acid, polymyxin B, and cephalothin. In addition, by 16S rDNA sequencing M. mucogenicum is more closely related to the M. fortuitum group than to the M. chelonae-abscessus group (160). The type strain (ATCC 49650^T) of M. mucogenicum differs by 11 to 18 bp from members of the M. fortuitum group but differs by 35 bp from M. abscessus and by 38 bp from M. chelonae. Hence, we propose to add this species to other members within the M. fortuitum group.

(v) M. senegalense. M. senegalense was originally described by Chamoiseau in 1973 as a subspecies of M. farcinogenes (34). Later, however, it was recognized as a different species closely related to M. fortuitum (137). Like M. peregrinum, M. senegalense is positive only on mannitol, when tested on common sugars, but has a unique PRA pattern with the hsp65 Telenti fragment (165, 174). Its 16S rDNA sequence differs by 4 bp from the unnamed M. fortuitum third biovariant complex (sorbitol-positive) strain ATCC 49403; by 5 bp from the unnamed third biovariant complex (sorbitol-negative) strain ATCC 49404; and by only 8 bp from M. fortuitum (ATCC 6841^T). By DNA comparison studies, however, it is a species apart from these other organism groups.

Type of disease. (i) Community-acquired disease. The M. fortuitum group accounts for 60% of cases of localized cutaneous infections caused by RGM but is a rare cause of chronic mycobacterial pulmonary disease (1, 3, 203, 205). Localized cutaneous disease generally occurs in previously healthy hosts, and drug-induced immune suppression appears to result in minimal increase in this risk. Wallace et al. (203) studied 123 patients with extrapulmonary disease caused by RGM and reported that 76 (63%) of these infections were due to the M. fortuitum group. Griffith et al. (63) studied 154 patients with pulmonary disease due to RGM and reported that only 16% of the infections encountered during the 15-year study were due to the M. fortuitum group (63). The M. fortuitum group was a common lung pathogen (50% of cases) only in the setting of chronic aspiration secondary to underlying gastroesophageal diseases such as achalasia. Approximately 25% of M. fortuitum group infections based on one study (205) have been associated with a variety of diseases other than skin or soft tissue infections including cervical lymphadenitis, mastoiditis, and meningitis. (91, 202, 205). Species in the M. fortuitum group are relatively rare causes of disseminated disease compared to other pathogenic RGM species, especially M. chelonae and M. abscessus.

(ii) Health care-associated disease. The M. fortuitum group is responsible for the majority (60 to 80%) of cases of postsurgical wound infections and catheter infections caused by the RGM (77, 134, 198). Most of the responsible organisms are M. fortuitum and are detailed below in the specific section on M. fortuitum (38, 198).

Geography. Cutaneous disease caused by the M. fortuitum group, although reported from all over the United States and worldwide, has been recognized most commonly in the southeastern United States (9, 198, 220). A report in 1989 (198) indicated that about 80% of wound isolates related to cardiac surgery were from seven southern coastal states: Texas, Louisiana, Georgia, Maryland, Alabama, Florida, and South Carolina. A second report published in the same year found that 92% of 37 identified cases of surgical wound infections following augmentation mammaplasty were in patients from southern coastal states, with the majority being from Texas, Florida, and North Carolina (201). Approximately 80% of isolates in both studies combined belonged to the M. fortuitum group.

Individual taxa. (i) M. fortuitum. (a) Community-acquired disease. In essentially all series of community-acquired or health care-associated disease attributed to the M. fortuitum group, most or all of the cases are due to M. fortuitum. In a study of 154 patients with RGM pulmonary disease, Griffith et al. (63) reported 13% of infections were due to M. fortuitum and only 3% were due to other members of the M. fortuitum group. In a series of cases of extrapulmonary disease cased by the M. fortuitum group, Wallace et al. (205) reported that almost 80% of the infections were due to M. fortuitum. Disseminated infections with M. fortuitum are rare. The first case report appeared in 1990, when Sack (145) described a patient with a history of intravenous IV drug abuse and AIDS, who had cutaneous lesions from which M. fortuitum was isolated. Cultures of specimens from lymph nodes, urine, pleural effusions, and feces all yielded M. fortuitum.

(b) Health care-associated disease. M. fortuitum has been implicated in numerous outbreaks of hospital or health care-associated infections (70, 77, 189). These include sternal wound infections; postinjection abscesses related to electromyography needles (72, 115); and a respiratory disease outbreak in Washington, D.C. (24). M. fortuitum has also been recovered from sporadic cases of surgical wound infections and catheter-related infections and is the most common RGM species in women with surgical wound infections following augmentation mammaplasty (189, 201). Details of some of the outbreaks are listed below.

Cardiac disease outbreaks. Isolates of M. fortuitum have been found in sternal wound infections in Hong Kong, Colorado, Nebraska, and Texas (189). Interestingly, three of the four involved multiple RGM species or multiple strains of the same species. The first outbreak occurred in 1976 in a hospital in Colorado. Of nine patients who underwent cardiovascular surgery within a 2-week period, four became infected with a single genetic strain (70) of M. fortuitum. Despite intense infection control efforts to recover the organism from environmental sources and subsequent molecular analysis of the isolates recovered, no environmental source was identified (70, 198).

In 1981, Preheim and colleagues (L. C. Preheim, M. J. Bittner, D. K. Giger, and W. E. Sanders Jr., Program Abstr. 22nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. 564, 1982) reported an outbreak in a Nebraska hospital that involved five patients who developed sternotomy infections following coronary bypass surgery. All had multiple debridements. One patient died (Preheim et al., 22nd ICAAC). Later analysis by plasmid profiles (198), multilocus enzyme electrophoresis (MEE), and pulsed-field gel electrophoresis (70) showed the presence of two strains of M. fortuitum.

Another outbreak in 1981 involving M. abscessus and M. fortuitum, was reported in a hospital in Corpus Christi, Tex. (87). Of 51 patients undergoing surgery over a 6-month period, 6 (11.3%) developed infections with one of these RGM. One patient with sternal wound infection due to M. fortuitum died as a result of complications from sternectomy and antimicrobial therapy. A subsequent study was performed in which culture media were inoculated with samples taken from environmental sites including the municipal water system, water from the cold water tap in the operating room, ice machines, swabs of lamps, oxygen tanks, suction apparatus, and commercial bone wax. Multiple sites were culture positive for M. fortuitum strains (87) which, by MEE and subsequent pulsed-field gel electrophoresis, were identical to the disease strains (70, 189, 198). This is the first and only cardiac surgery outbreak in which the piped-water system has been implicated as the source of the pathogenic RGM. In this case, the cardioplegia solution was cooled in ice made from tap water contaminated with the outbreak strains.

The fourth and latest outbreak of M. fortuitum infection following cardiac surgery came from Hong Kong (220). Both M. fortuitum and M. peregrinum were implicated. The outbreak spanned the years 1987 to 1989, and 7 (33%) of 21 wound infections were due to M. fortuitum. (Details of the M. peregrinum strains are presented in the M. peregrinum section, below.) Subsequent ribotyping and susceptibility testing suggested that multiple strains were involved (220, 221). No source for the prolonged Hong Kong outbreak was identified.

Postinjection abscess disease. Most outbreaks of postinjection abscesses caused by RGM have involved M. abscessus. However, Nolan et al. (115) reported an outbreak of M. fortuitum in five (83%) of six patients undergoing electromyography at a facility in Washington state. The outbreak was traced to a break in a manual procedure used for sterilizing the reusable needle electrodes. When subsequent sterilizations were performed using an autoclave, no further cases were reported (115).

Plastic surgery-related disease. No large outbreaks of wound infection following plastic surgery due to M. fortuitum have been reported, but sporadic wound infections following plastic surgery have been well documented (205). Many of these infections, involving M. fortuitum, occurred after augmentation mammaplasty (201). A study by Wallace et al. (198) identified 37 cases of surgical wound infection with RGM following augmentation mammaplasty. Of these isolates, 26 (70%) were identified as M. fortuitum. Several surgeons had more than one case, suggesting that local environmental factors were important to disease development. Six cases of M. fortuitum disease associated with spontaneous breast abscesses with no history of surgery or trauma were also reported.

Pseudo-outbreaks. One pseudo-outbreak involving M. fortuitum occurred in 1987 in Houston, Tex., and involved ice contaminated with M. fortuitum. Although M. fortuitum was recovered from specimens from four patients who underwent bone marrow aspiration, none of the patients had evidence of disease due to M. fortuitum. It was later noted that each of the patients whose aspirates yielded M. fortuitum on culture also had viral cultures performed, and this required that the syringe containing the aspirate be plunged into ice for transport. Samples taken from the ice machine located on the same floor as the patients with positive aspirate samples were also positive for M. fortuitum. Samples from ice machines on other floors did not grow M. fortuitum (76). No molecular typing was performed.

(ii) Unnamed third biovariant complex including M. septicum, M. mageritense, M. houstonense (proposed), and M. bonickei (proposed). Pattyn et al. (124) published one of the earliest studies of the unnamed third biovariant complex approximately 30 years ago. The authors commented that most of the isolates they studied were environmental strains and none had a definite disease association.

(a) Community-acquired disease. In 1991, Wallace et al. (192), characterized 85 clinical isolates of unnamed M. fortuitum third biovariant complex, all of which were disease associated. These represented 16% of 410 isolates of the M. fortuitum group submitted to a Texas laboratory and 22% of 45 isolates submitted to the Queensland, Australia, state laboratory. Over 75% of the infections involved skin, soft tissue, or bone. Clinical histories were available for 52 patients with skin and soft tissue infections, and the type of injury responsible for infection was reported for 42 patients. Of these 42 patients, 29% had osteomyelitis confirmed by bone biopsy. Most infections occurred following puncture wounds or compound (open) fractures. Only two patients (children) had no history of trauma leading to their infection. Metal puncture wounds (48%) or motor vehicle accidents (26%) were the most common histories given, and approximately 40% of the injuries involved the foot or leg. Stepping on a nail was the classic scenario (194). No cases of disseminated disease were observed in this study, and, to date, none have been reported by other authors. This study also identified 26 isolates of the third biovariant complex from pulmonary sources. Clinical significance was not determined, but almost certainly some of these were disease producing. None of these isolates were studied by molecular methods that would identify them as one of the recently described species within the complex (i.e., M. houstonense [proposed], M. bonickei [proposed], M. septicum, or M. mageritense) (190; Schinsky et al., submitted).

(b) Health care-associated disease. A small number of cases have been reported in association with hospital-acquired disease in other studies, including wound infections following cardiac surgery (198) and augmentation mammaplasty (201).

(c) Geography. The original description by Pattyn et al. (124) of this group was based on isolates from Europe and Africa. Later in 1983, Levy-Frébault et al. characterized 23 additional isolates of M. fortuitum from France and found 6 environmental isolates that were identified subsequently as M. fortuitum unnamed third biovariant complex (95). A later study by Wallace et al. included 10 isolates from Australia. The remaining 70 isolates were from the United States, of which approximately 70% were from Texas, 6% were from Florida, and 5% were from Alabama and Georgia (194). Four percent or less of the third biovariant isolates identified in this study were from other states including Tennessee, Louisiana, New Hampshire, South Carolina, Arkansas, and Connecticut (our unpublished data).

(iii) M. peregrinum. Currently, there is no published series or review evaluating the clinical significance of M. peregrinum. No case of disseminated infection due to M. peregrinum has been reported. However, a small number of cases of sporadic infections have been reported and have been associated with diseases similar to other members of the M. fortuitum group. These include chronic lung disease (63, 64), sternal wound infections (198), and cutaneous disease (205). In general, they represent only 1 to 2% of sporadic community-acquired or health care-associated infections due to RGM. M. peregrinum has been reported as a cause of a pseudo-outbreak of respiratory disease due to a contaminated ice machine (93) and as the etiologic agent of 67% of cases in an outbreak of sternal wound infections from Hong Kong that occurred from 1987 to 1989 (220, 221).

(iv) M. mucogenicum. M. mucogenicum (160), formerly MCLO, was originally discovered in two outbreaks of peritonitis in 1976 and 1978, in 5 (18%) of 22 and 5 (63%) of 8 patients, respectively, undergoing intermittent chronic peritoneal dialysis (5). Infections were traced to the use of contaminated automated chronic peritoneal dialysis machines in two dialysis centers. Seven sporadic cases of peritonitis due to M. mucogenicum from the same two centers were also diagnosed. The investigators' findings (5) suggested that ineffective disinfection of the equipment followed by colonization of the machines by this newly described species was responsible for the outbreaks. Three studies showed that M. mucogenicum, like other pathogenic species of RGM, is relatively resistant to formaldehyde and glutaraldehyde disinfectants, which are typically used to disinfect dialysis equipment (5, 31, 69). In 1985, Bolan et al. (12) described a mycobacterial disease outbreak in a hemodialysis center in Louisiana. Of 26 identified isolates, 25 were M. abscessus and 1 was M. mucogenicum. The single factor common to all patients was their exposure to hemodialyzers (artificial kidneys) that had been ineffectively treated with concentrations of disinfectant (formaldehyde) that were below effective levels for these RGM species (12). Although M. mucogenicum is often recovered as a laboratory contaminant, these three outbreaks alert us to the potential significance of this waterborne organism.

In 1993, Wallace et al. (200) evaluated 87 sporadic isolates of M. mucogenicum. Of these isolates, 54 (62%) were respiratory, and only 2 (4%) of them (both from patients with AIDS) were clinically significant. For the remaining 33 nonrespiratory isolates, significant clinical diseases included posttraumatic wound infections and catheter-related sepsis. Recovery of M. mucogenicum from skin, wound, or blood cultures was most often associated with clinical disease. In contrast, a single positive sputum culture is almost never clinically significant. Goldblatt and Ribas (61) recently reported the first case of a patient with granulomatous hepatitis caused by M. mucogenicum. No cases of disseminated cutaneous disease due to M. mucogenicum have been reported. The frequent presence of this organism in tap water, including ice machines (39), may contribute to the transient colonization or contamination of sputum samples (200). In a study of 113 mycobacterial isolates from tap water samples from various geographic sites, the most frequently occurring nontuberculous mycobacterium (41%) was M. mucogenicum (39). This study underscores the potential health risks of these ubiquitous organisms.

M. mucogenicum was first described by Band et al. (5) in the peritonitis outbreak in Washington state. Since that time, isolates have been recovered from Texas, Arizona, Maryland, Delaware, Illinois, Pennsylvania, Missouri, Florida, Washington D.C. and California (R. J. Wallace, Jr., unpublished data).

(v) M. senegalense. M. senegalense is an etiologic agent of farcy, a disease of skin and superficial lymphatics in African bovines (208). It has not been reported from environmental or clinical cultures in the United States or Europe.

(vi) M. septicum. The type strain of M. septicum (ATCC 700731^T) was recovered in Australia from three separate blood cultures and a central venous catheter tip after its removal (74, 152). No other isolates have been reported.

Historical perspective. In 1953, Moore and Frerichs recovered an RGM (now ATCC 19977^T) from a knee abscess. The authors thought the isolate was distinctive biochemically and morphologically from other RGM and identified it as a new species, M. abscessus. This name was selected because of the ability of the organism to produce deep subcutaneous abscesses (111).

Stanford et al. (163) first reported studies on clinical isolates of what was then known as M. borstelense (125). Among the isolates they studied were isolates from postinjection abscess outbreaks in Holland and England, human strains from other parts of Europe and Africa, and environmental strains. This study resulted in the official adoption of the name "M. chelonei" for these isolates, a name which was later changed to the more correct Latin, M. chelonae.

Many early investigators, however, believed M. chelonae and M. abscessus to be the same organism because they showed almost identical biochemical features. A cooperative numerical phenotypic study by the International Working Group on Mycobacterial Taxonomy (IWGMT) published in 1972, however, demonstrated that the two taxa were sufficiently different to be classified as subspecies and renamed them M. chelonae subspecies chelonae and M. chelonae subspecies abscessus (86).

Using genomic DNA-DNA hybridization studies, M. chelonae subspecies abscessus (ATCC 19977^T) was later shown to be a separate species on the basis of <70% genomic homology with other RGM taxa, including M. chelonae subspecies chelonae (ATCC 35752^T) (96). In 1992, Kusunoki and Ezaki elevated M. abscessus comb. nov. to species status, and M. chelonae subsp. chelonae once again became M. chelonae (89). Interestingly, by 16S rDNA sequencing, M. chelonae and M. abscessus differ by only 4 bp and are examples of the few different nontuberculous mycobacterial species that have identical 16S rDNA hypervariable region A sequences (89).

M. immunogenum, formerly M. immunogen, is a newly described RGM first recognized in contaminated metalworking fluids (110). It is closely related to M. chelonae and M. abscessus but readily distinguished by genetic methods (212). The organism was named for its potential relationship to cases of hypersensitivity pneumonitis in factory workers (metal grinders) who used mycobacterium-contaminated metal-grinding fluids for lubrication and cooling of their machines. By 16S rDNA sequencing, the ATCC type strain ATCC 700505^T differs by only 8 bp from M. abscessus and by 10 bp from M. chelonae. It is morphologically similar to M. abscessus but has a different drug susceptibility pattern and a different PCR restriction analysis pattern of the hsp65 Telenti fragment (212).

Type of disease. (i) Community-acquired disease. For several years prior to the current molecular microbiology era, the M. chelonae-abscessus group was referred to collectively as M. chelonei or M. chelonae without further differentiation of species (see "Taxonomy and clinical significance above"). The M. chelonae-abscessus group has been associated with a variety of different diseases.

The most common clinical disease is probably chronic lung disease, usually in elderly women with bronchiectasis or young adults with cystic fibrosis (CF). The M. chelonae-abscessus group is responsible for approximately 95% of disseminated cutaneous infections caused by the RGM. Unlike patients with a localized infection, patients with disseminated cutaneous disease have multiple painful draining small abscesses that involve the arms and legs. Localized cellulitis, osteomyelitis, and small-joint arthritis are also commonly associated with the M. chelonae-abscessus group.

(ii) Health care-associated disease. Sporadic (single) cases of otitis media, following tympanostomy tube placement, catheter infections, and postsurgical wound infections following a variety of surgical procedures (especially plastic surgery) also have involved this group of RGM (53, 98, 130, 135, 205). The M. chelonae-abscessus group has been involved in several health care-associated disease outbreaks including post-cardiac surgery sternal wound infections and vein graft site infections (87). Other outbreaks of M. chelonae-abscessus group infection have involved plastic surgery (52, 146), hemodialysis, and miscellaneous outbreaks including wound infections following laparoscopy, liposuction (107), and post-tympanostomy tube placement (98). Additionally, postinjection abscess outbreaks following the use of multidose vials (15, 62, 129) or contaminated biologicals (30, 33, 57, 183) also have been reported. Vaccine-related outbreaks involving M. chelonae-abscessus as contaminants also are recorded (59, 119). (Isolates from most outbreaks since 1980 were restudied at a later date and shown to be M. chelonae or M. abscessus. These outbreaks are detailed under the specific species.)

In addition to these true outbreaks of infection, several health care-associated pseudo-outbreaks have been described in conjunction with contaminated or malfunctioning bronchoscopes (66, 116, 121, 211; K. Petersen, N. Bus, V. Walter, and C. Chenoweth, Abstr. Infect. Control Hosp. Epidemiol., abstr. S-32, 1994), automated endoscope-cleaning machines (54, 55), and contaminated laboratory reagents (90).

Geography. The M. chelonae-abscessus group is a collection of ubiquitous organisms found in soil and water worldwide. Outbreaks of M. chelonae-abscessus group disease have occurred primarily in the United States in southern coastal states and have been reported in North Carolina (54, 98), Louisiana, Georgia, Florida, and Texas (198). Generally, almost all of the states in the southern United States have reported disease with M. abscessus (70, 224). Outside the United States, isolates have been recovered from Hungary (205), Japan, Germany (6), Canada (53), France, Italy, Sweden, Australia, Belgium, Switzerland, Colombia, South America (183), and the United Kingdom (70; unpublished data).

Individual taxa. (i) M. chelonae. M. chelonae is one of the most antibiotic- resistant species of the pathogenic RGM. Like M. abscessus, M. chelonae is involved in several different types of community-acquired infections.

(a) Community-acquired disease. Pulmonary disease. Unlike M. abscessus and M. fortuitum, M. chelonae is only rarely a cause of chronic lung disease. In the series of 154 patients with chronic lung disease due to RGM reported by Griffith et al. (63), only 1 of 146 isolates identified to species was an M. chelonae.

Disseminated disease. M. chelonae causes three basic types of cutaneous disease (see Table 1). The most common type is disseminated cutaneous disease, which occurs when the host is chronically immunosuppressed (4). Wallace et al. (195, 206) reported that 53% of 100 clinical skin and/or soft tissue and/or bone isolates of M. chelonae were from patients with disseminated cutaneous infections (193). These infections were seen in patients receiving long-term corticosteroids and/or chemotherapy, primarily because of underlying organ transplantation, rheumatoid arthritis, or other autoimmune disorders (206). Chronic lung disease, solid-tumor malignancies and other disorders were less frequently associated with this disease (185, 222). McWhinney et al. (104) described three cases of M. chelonae in febrile neutropenic patients receiving chemotherapy. Infections with M. chelonae have occurred predominantly in patients with drug-induced immunocompromised status. In contrast, disease states which lead to immune suppression, such as AIDS, have not been significant risk factors for the development of disseminated M. chelonae infection.

Localized infections. The second type of infection seen with M. chelonae involves community-acquired localized infections following trauma (62, 205, 206, 210). These infections range from localized cellulitis or abscess to osteomyelitis. In the series by Wallace et al., 35% of the infections caused by M. chelonae were of this group (i.e., localized wound infections) (Table 1) (193).

(b) Health care-associated disease. Sporadic localized wound infections following medical or surgical procedures including needle injections can occur with M. chelonae but are rare compared to infections with M. fortuitum and M. abscessus. Health care-associated outbreaks due to M. chelonae are also rare and have been observed only following injection with contaminated syringes or needles, the implantation of contaminated porcine heart valves (55, 79, 189), and, recently, the use of liposuction (107). In this last outbreak, the organism was recovered from tap water connected to the suction cannulas.

The third, and least common, type of infection caused by M. chelonae, yet the most common type of health care-associated disease, is that of catheter-related infections (Table 1). In 1992, Wallace et al. reported that 8 of 100 clinical isolates of M. chelonae were associated with intravenous catheters, an additional 3 involved chronic peritoneal dialysis catheters, and 1 involved a hemodialysis shunt (193). They found that both the use of corticosteroids and renal failure were risk factors for these catheter-related infections (193).

(ii) M. abscessus. M. abscessus and M. chelonae are probably the most antibiotic resistant species of the pathogenic RGM. Like M. chelonae, M. abscessus is involved in a variety of different types of community-acquired infections.

(a) Community-acquired disease. Pulmonary disease. Pulmonary disease accounts for most clinical isolates of this species (Table 1). According to Griffith et al. (63), the majority (82%) of the 146 disease-associated pulmonary RGM isolates identified to species over a 15-year period by a Texas reference laboratory were M. abscessus. In patients with M. abscessus pulmonary disease, underlying diseases included bronchiectasis, CF (40), gastroesophageal disorders, and prior granulomatous disease such as sarcoidosis or tuberculosis. The analysis by Griffith et al. (63) of M. abscessus pulmonary disease emphasized striking similarities to pulmonary M. avium complex lung disease of the type known as nodular bronchiectasis. The latter presents as an indolent course, occurs predominantly in elderly nonsmoking female patients, and exhibits a possible geographic disposition (i.e., southern coastal states have 69 to 75% of the cases). These similarities suggest a common pathogenicity or host susceptibility (63). Like patients infected with M. avium complex, most patients with pulmonary disease due to M. abscessus have underlying bronchiectasis of a type known as nodular bronchiectasis (196). Approximately 20% of patients with M. abscessus infection will also develop infection or disease due to M. avium complex (63), again emphasizing similar if not identical risk factors. There is controversy about whether M. abscessus can be a "colonizer" in the lungs. These authors believe that true colonization does not exist and that patients with minimal symptoms just have minimal disease. Repeated isolation of M. abscessus from the respiratory tract is usually associated with significant lung disease.

Pulmonary disease in patients with CF. M. abscessus patients with underlying CF deserve some special comments. The recovery of M. abscessus from the respiratory tracts of patients with CF is being noted with increasing frequency. Patients with CF are predisposed to airway and parenchymal infections for several reasons, including the nature of CF disease and the usual associated bronchiectasis (48). The primary risk factor that makes patients with CF more susceptible to mycobacterial disease is thought to be bronchiectasis. Evaluation of the significance of the mycobacterial infection can be complicated because isolation of other organisms such as Pseudomonas aeruginosa often makes isolation and interpretation of the clinical significance of the RGM difficult. After M. avium complex, M. abscessus is the second most common species of nontuberculous mycobacteria recovered from respiratory specimens in patients with CF (149).

Lung transplantation may be considered a therapeutic option in some CF patients. However, the posttransplantation immunosuppressive therapy increases the risk of both the development and the dissemination of nontuberculous mycobacterial infections. Patients with CF and M. abscessus lung disease carry the risk of developing disseminated infections, including cervical adenitis, following transplantation (48, 168).

Extrapulmonary disease. After M. fortuitum, M. abscessus is the second most common RGM species in clinical specimens; it also produces a wide variety of extrapulmonary diseases. Wallace et al. (205) studied a series of 59 nonrespiratory isolates belonging to the M. chelonae-abscessus group and found that M. abscessus cases outnumbered M. chelonae cases more than 2:1 (30 and 12 cases, respectively). Among the 30 cases of nonpulmonary disease caused by M. abscessus, 43% were postsurgical or postinjection wound infections, 23% were localized community-acquired wound infections, 20% were disseminated cutaneous infections, and 13% were miscellaneous types of infections including keratitis and prosthetic valve endocarditis.

Of the 23% of nonpulmonary disease cases resulting in localized infection, most characteristically developed following a break in the skin surface and subsequent direct contact with contaminated water or soil. Localized trauma with a resulting pyogenic abscess is sometimes followed by a sporotrichoid appearance of ascending lymphadenitis predominantly in immunocompromised patients (81). Other examples of localized M. abscessus wound infections include a soft tissue infection of the cheek following an insect bite (26) and a case of vertebral osteomyelitis (102).

(b) Health care-associated disease. M. abscessus and M. fortuitum are the most common mycobacterial species causing nosocomial disease, especially sporadic and clustered outbreaks of surgical wound infections. As noted above (205), surgical wound infections represented 43% of clinical cases of nonpulmonary infections due to this species. Disease outbreaks have been described after augmentation mammaplasty, facial plastic surgery, cardiac surgery, injections of alternative medicines, steroid injections, and miscellaneous types of surgery (55, 223).

In the largest outbreak of RGM-mediated postinjection abscesses, which occurred in an alternative medicine clinic in Colombia, South America (183), 205 (59%) of 350 of patients developed localized cutaneous abscesses or cellulitis due to M. abscessus. Another large M. abscessus outbreak in the United States resulted from the injection of an unlicensed product sold as adrenal cortex extract (ACE) (57). Of 140 persons known to have received the ACE injections, 87 subjects (62%) from 16 states were identified as infected. M. abscessus was cultured from seven vials of ACE, six of which were unopened. Isolates from both patients and opened and unopened vials of ACE were typed by MEE and pulsed-field gel electrophoresis and shown to be identical (57). Pseudo-outbreaks related to contaminated bronchoscopes have also been attributed to M. abscessus (55).

Although disseminated M. abscessus disease is relatively unusual, it is serious. Most cases have occurred in chronically immunosuppressed patients receiving corticosteroids, and the disease has no apparent portal of entry. The disease presents as multiple draining cutaneous nodules, usually involving the lower extremities. Patients with disseminated infection have rarely included detectable bacteremia and endocarditis (41), and these cases can occur as a complication of localized infections. This is especially true in patients on hemodialysis. Bolan et al. (12) reported 25 infections due to M. abscessus in a hemodialysis center in Louisiana (see the section on M. mucogenicum [above] for details). Nine of these patients had widely disseminated disease. Subsequent molecular studies using random amplified polymorphic DNA-PCR showed that the M. abscessus strains from the water supply and the clinical isolates were identical (224).

This hemodialysis outbreak not only served to show the potential virulence of RGM disease in this setting but also pointed out the relative resistance of these organisms to commonly used disinfectants, a fact which increases the risk of health care-associated infections. In the Louisiana outbreak, investigators discovered that formaldehyde concentrations lower than 2% were used in disinfecting the reusable hemodialyzers. Failure to maintain a 2% concentration probably played a large role in this outbreak because this concentration had been previously established (31) as the minimum concentration to which M. abscessus was susceptible in vitro (12). Five years later, Lowry et al. (97) reported M. abscessus infection in five patients receiving dialysis with reusable dialysis tubing at another outpatient hemodialysis clinic. Again, the disinfectant used (2.5% Renalin) appeared to play a role, since at this concentration it did not completely kill the M. abscessus recovered from the patients and from the dialyzers that were manually reprocessed (97).

(iii) M. immunogenum. In 2000, Moore et al. (110), described an outbreak of hypersensitivity pneumonitis among workers in an industrial plant that was undergoing extensive remodeling and renovation. The workers utilized cutting, drilling, and grinding machines and worked with a semisynthetic metalworking fluid that was sprayed on the machines to keep them cool. Part of the outbreak investigation involved performance of cultures of the metalworking fluid for mycobacteria. Twenty- five isolates were recovered from different samples throughout the plant that were similar to M. chelonae-abscessus complex but with a unique hsp65 PRA pattern. This finding launched a search for other M. chelonae-abscessus-like RGM isolates with the same RFLP pattern. Isolates with this PRA pattern were identified from unrelated nosocomial pseudo-outbreaks involving contaminated endoscopes and from patients with serious infections. Although these strains exhibited overlapping biochemical and HPLC features with M. chelonae and M. abscessus, they differed from clinical and reference strains of both these species (54, 212) and most isolates had a unique susceptibility pattern of resistance to both cefoxitin and tobramycin (212). Molecular examination that included DNA homology studies showed that these isolates belonged to a separate species, which has been proposed as M. immunogenum (212). M. immunogenum organisms are able to grow and survive in degraded metalworking fluid (110), although it has not yet been established whether these organisms can metabolize any of the constituents of the fluid or additive materials for nutrition. The presence of other microorganisms (especially aerobic gram-negative bacilli) in degraded metal-grinding fluids and the use of biocides probably facilitates fluid degradation and subsequent growth of this species (110).

(a) Clinical disease. In the only detailed study of clinical disease, 11 isolates of M. immunogenum were identified from patients (212). Three came from cultures of blood from patients with catheter- or pacemaker-related sepsis; two came from cutaneous cultures of samples from a liver transplant recipient and an infant with severe combined immunodeficiency syndrome with disseminated cutaneous infections; two came from catheter exit sites; and one each came from fluid a septic joint in a hand, bronchoalveolar lavage fluid from a patient with chronic pneumonia, a cornea from a patient with suspected keratitis, and urine from a patient with an unknown diagnosis (212).

Additionally, two pseudo-outbreaks have been reported from Kentucky and Missouri, involving contaminated automated bronchoscopic washing machines which ultimately led to contaminated bronchoscopes (54, 55, 100, 207), retrospect, these infections were found to be due to M. immunogenum (212).

One important distinguishing feature of isolates of the M. smegmatis group, in contrast to the M. fortuitum group and the M. chelonae-abscessus group, is their general lack of susceptibility to the new macrolides, including clarithromycin (17). Since clarithromycin has been considered the cornerstone of antimicrobial therapy for RGM disease, it becomes vital to identify RGM isolates to exclude groups like the M. smegmatis group and the M. fortuitum third biovariant complex sorbitol-positive group, which are intrinsically resistant to this class of drugs.

Historical perspective. The M. smegmatis group, first isolated by Lustgarten in 1885, was named for the genital secretions (smegma) from which it was recovered in a patient with a penile ulcer (99). The first well-described case of human disease caused by the M. smegmatis group involved the lungs and pleura of a patient with underlying exogenous lipoid pneumonia and was reported less than 15 years ago (184).

Type of disease. (i) Community-acquired disease. The first series of clinical patients was reported by Wallace et al. in 1988 (199) when they characterized 22 clinical isolates. The authors noted that the isolates were heterogeneous, and fell into three groups with different antibiotic susceptibility patterns. Later, in 1999, these three groups were studied in greater detail, including DNA homologies, and were found to be three distinct species: M. smegmatis sensu stricto, M. wolinskyi, and M. goodii (17). The last two names honored Emanuel Wolinsky and Robert Good, two early leaders in the field of nontuberculous mycobacteriology (17).

The three species are separated with approximately 90% accuracy on the basis of tobramycin susceptibility. M. smegmatis sensu stricto is tobramycin susceptible (MIC, 1µg/ml; agar disk diffusion zone, >30 mm). M. goodii has intermediate susceptibility to tobramycin (MIC, 2 to 8 µg/ml; agar disk diffusion zone, 11 to 30 mm), and M. wolinskyi is resistant to tobramycin (MIC, >8 µg/ml; agar disk diffusion zone, 10 mm) (17).

The HPLC patterns produced by M. smegmatis sensu stricto, M. wolinskyi, and M. goodii can be differentiated from those produced by members of the M. fortuitum group (16; K. C. Jost, Jr., S. H. Chiu, R. B. Dunlap, L. B. Elliott, B. A. Brown, V. A. Steingrube, R. W. Wilson, and R. J. Wallace Jr., Abstr. 99th Gen. Meet. Amer. Soc. Microbiol. 1999, abstr. U-36, 1999), and the three species have different patterns. The overlap between patterns of all mycobacterial species makes identification of the individual M. smegmatis species difficult, however, when evaluating individual clinical isolates.

The most accurate separation of the three species within the M. smegmatis group is achieved by molecular techniques including PRA of the Telenti fragment of the hsp65 gene and 16S rRNA gene sequence analysis (17).

Until a case of lung disease proven by lung biopsy was reported in 1986 (184), the M. smegmatis group was considered to be an environmental saprophyte of no clinical significance. Community-acquired disease due to M. smegmatis group is now known to involve cellulitis, localized abscesses, and/or osteomyelitis of a wound site following a traumatic event. Newton et al. (113), reported that the M. smegmatis group was the causative agent of two cases of infection following motor vehicle accidents, with cellulitis and extensive soft tissue and periosteal necrosis evident at the time of surgical debridement. A few cases of lipoid pneumonia (pneumonia resulting from inhalation or aspiration of lipid-containing medicinals or food particles) with secondary mycobacterial infection have also been reported to be caused by the M. smegmatis group (17, 199). No case of disseminated cutaneous disease due to the M. smegmatis group has been reported to date.

(ii) Health care-associated disease. Health care-associated infections involving the M. smegmatis group have included sporadic cases of catheter sepsis, infected pacemaker site, sternal wound infection with possible osteomyelitis following cardiac surgery, and infections following plastic surgery (breast reduction surgery and a face-lift) (17, 199). No health care-associated disease outbreak or pseudo-outbreak due to the M. smegmatis group has yet been reported.

Geography. Isolates of the M. smegmatis group have a wide geographic distribution. Isolates have been recovered in the United States from Texas, Alabama, California, Florida, Illinois, Indiana, Massachusetts, Minnesota, Mississippi, Missouri, North Carolina, Ohio, Oklahoma, South Carolina, Utah, and Wyoming (17, 56, 199). Outside the United States, isolates have been reported from Australia, Russia, Canada, and Switzerland (17, 127, 199).

Individual taxa. (i) M. smegmatis sensu stricto. In 1988, Wallace et al. (199), reported a series of 21 patients with infections due to the M. smegmatis group. In the latter taxonomic study of these isolates published in 1999 (17), 52% of the 21 original clinical isolates matched the type strain and additional ATCC reference strains of M. smegmatis and hence were renamed M. smegmatis sensu stricto. With expansion of the number of clinical isolates which met the criteria for the M. smegmatis group to 71, 49% were M. smegmatis sensu stricto (17). These isolates had a unique mycolic acid pattern and were susceptible to tobramycin agar disk diffusion (zones, >30 mm with a 10 µg commercial disk). Additionally, 16S rRNA gene sequence analysis and PRA of the 439-bp hsp65 gene sequence were unique to this species (17). Isolates of M. smegmatis sensu stricto have been reported from several states including Florida, Wyoming, South Carolina, Texas, Mississippi, and Illinois and, outside the United States, in Australia (199).

M. smegmatis sensu stricto has been incriminated in community-acquired cases of lymphadenitis, cellulitis, osteomyelitis, wound infections and, rarely, respiratory disease, usually associated with exogenous lipoid pneumonia (17, 199). It has been recovered from health care-associated infections, including sternal wound sites following cardiac surgery, bacteremia from intravenous catheter placement, and breast abscess following augmentation mammaplasty (17, 199).

(ii) M. goodii. As mentioned previously, the Wallace study in 1988 (208) launched a second study, published in 1999 (17), which identified 8 of 21 isolates reported in the 1988 publication and 20 new isolates in the second study which proved to be M. goodii. These 28 isolates represented 39% of the 71 total isolates of the M. smegmatis group studied. They had a mycolic acid pattern that differed from the other two species in the group, were intermediately susceptible to tobramycin by agar disk diffusion (zones, 11 to 30 mm), had a unique 16S rRNA gene sequence, and a unique PRA pattern (159). M. goodii is the second most frequently isolated species within the M. smegmatis group.

Isolates of M. goodii have been recovered from California, Texas, Florida, Alabama, Minnesota, Utah, Oklahoma, Missouri, Indiana, Ohio, North Carolina, and Massachusetts (17, 199). Outside of the United States, isolates have been reported from Russia (17, 56), Australia (17, 199) and Canada (Sylvia Chomyc, Provincial Laboratory of Public Health, Alberta, Canada, personal communication).

Isolates of M. goodii have been recovered from cases of cellulitis, bursitis, and osteomyelitis after open (compound) fracture or penetrating trauma (17, 56, 199). A few cases of respiratory disease due to M. goodii have been reported. Most have been associated with underlying exogenous lipoid pneumonia with pulmonary infiltrates, similar to M. smegmatis sensu stricto (17, 199).

M. goodii has been involved in several types of sporadic health care-associated disease, including bacteremia with catheter sepsis (199), cardiac bypass infection with osteomyelitis, infected pacemaker site, and infection following breast reduction surgery (17).

(iii) M. wolinskyi. Of 21 isolates from the 1988 study by Wallace et al. (199), 2 matched 6 other isolates in the second study (17) in their