TABLE 7

Continuously monitored broth culture instrument systemsa

System(s)bDescriptioncAdvantage and limitation(s) (reference)
BD Bactec MGIT automated mycobacterial systems (960 and 320 systems, depending on vol; BD Diagnostic Systems, Sparks, MD)System automatically detects tube placement, i.e., scan-and-load technology; uses MGIT medium containing patented sensors that detect oxygen consumption, indicating mycobacterial growth; PANTA antibiotic mixture is added to the MGIT tube prior to inoculation; a fluorescent compound, embedded in silicone in the tube bottom, is quenched by the presence of oxygen, but when the oxygen is metabolized by mycobacteria or another microorganism, the compound fluorescesTime to detection is much shorter with this system than with solid media; mycobacterial growth, including M. tuberculosis complex, M. xenopi, and various other NTM, can go undetected by the instrument (337); tubes should be visually inspected for clumps before the tubes are discharged as negative (338)
BacT/Alert Mycobacteria detection system (bioMérieux, Durham, NC)Utilizes a colorimetric sensor and reflected light to monitor the presence and production of CO2; the sensor changes color because of CO2 produced by the metabolic activity of mycobacteria and other microorganisms; enrichment fluid containing bovine serum albumin, sodium chloride, oleic acid, and saponin is added; bottles contain antibiotic mixture of amphotericin B, azlocillin, nalidixic acid, polymyxin B, trimethoprim, and additional growth factorsTime to detection is much shorter with this system than with solid media; mycobacterial growth can go undetected by the instrument; tubes should be visually inspected for clumps before the tubes are discarded as negative; negative cultures may also be checked by AFB smear and/or subcultured at some point prior to discarding the specimen as negative (339)
VersaTREK (ThermoFisher Scientific, Waltham, MA)Bottles contain antibiotic mixture of polymyxin B, vancomycin, nalidixic acid, and amphotericin B; each bottle is continuously monitored for changes in gas pressure, due to consumption of oxygen by mycobacteria and production of gas by their metabolic activityTime to detection is much shorter with this system than with solid media; at the end of the incubation period, a bottle not exhibiting a positive growth response should be visually inspected for turbidity (340)
  • a Mycobacterial blood culture methods in common use include visual inspection of processed blood (e.g., Isolator-10 system; Inverness Medical, Princeton, NJ) inoculated on solid medium, continuous detection in liquid medium inoculated with blood (e.g., BacT/Alert MB system or Bactec Myco/F Lytic system) (341), or processed blood (e.g., VersaTREK) (340). The turnaround times to detection for M. tuberculosis were 23.8 days for the Isolator-10 system, 20.0 days for the Myco/F Lytic system, and 16.5 days for BacT/Alert MB (341).

  • b See reference 1.

  • c PANTA, polymyxin B, amphotericin, nalidixic acid, trimethoprim, and azlocillin.