Table 5.

Differentiating features of the Basidiobolusand Conidiobolus species that cause disease in humans

Organism nameColony morphologyHyphal morphology
Basidiobolus ranarumFlat furrowed colonies with a waxy texture; yellowish to grayWide vegetative mycelium (8–20 μm wide), increasing in septation with age; sporangiophores are short and either narrow or with inflated apices        
Conidiobolus coronatusFlat, waxy colonies, becoming powdery, with a short aerial mycelium with age; petri dish lid becomes covered with conidia ejected from older cultures; colonies are white, buff, tan or brown      Wide vegetative mycelium (6–15 μm); conidiophores are short and unbranched
Conidiobolus incongruusSimilar to C. coronatus; dry colonies are produced, becoming more aerial with increased humidity    Wide vegetative mycelium (10–22 μm); conidiophores are 30–130 μm tall and inflate subapically
Conidiobolus speciesNot knownCoenocytic  
Sporangiole (conidia) morphologyZygospore production characteristicsOther
Round, single-celled conidia (7–15 by 6–12 μm) have flattened apices and retain a portion of their sporangiophore wall; they produce no papillated sporangioles; spores may be propelled by an ejected fluid stream or may be passively released; sporulation ability is rapidly lost in vitroHomothallic; thick, smooth-walled zygospores (20–50 μm in diameter) are produced; conjugation “beaks” are often present; chlamydospores (20–24 μm in diameter) are produced by older culturesModerately fast growth at 30°C, slower growth at 37°C, and poor growth at 15°C; colonies often produce a musty odor; disease seen most often in children
Round to pyriform single-celled conidia (25–45 μm wide) are bluntly papillated; villous sporangioles, covered with short hair-like projections, are made in abundance; conidia may sporangiolate, producing a “corona” of sporangioles; spores are forcibly ejected from hyphal elementsHeterothallic production of zygosporesGrows well when incubated from 25 to 37°C; no musty odor is produced; disease seen most often in adult men
Round to pyriform, single-celled conidia (16–30 by 20–34 μm) have prominent, pointed papillae and are produced in abundance; no villous sporangioles are producedHomothallic, occurring within 2 days of planting; zygospores are round, thick walled (20–21 μm), with no conjugation beaksGood growth at 37°C, little growth seen at room temperature
Forcibly discharged conidia measure 16 by 16.9 μmHomothallic; round, thick-walled zygospores (20–21 μm)Single case report of human disease