Carbon assimilation profiles as a tool for identification of Zygomycetes

Identification of Zygomycetes is difficult and time-consuming by standard microbiological procedures. Carbon assimilation profiles are commonly used for yeast-and bacterial-species identification but rarely for filamentous-fungus identification. Carbon assimilation profiles were evaluated using the commercialized kits ID32C and API 50 CH, which contain 31 and 49 tests, respectively, to serve as simple tools for species identification of Zygomycetes in clinical microbiology laboratories. Fifty-seven strains belonging to 15 species and varieties of Zygomycetes, including Rhizopus, Absidia, Mucor, and Rhizomucor species, were tested for intra- and interspecies variability based on their carbon assimilation profiles. Using ID32C strips, 6 tests were always positive, 7 were never positive, and 18 showed consistently different results between species. With API 50 CH strips, 15 tests were positive for all species, 13 were never positive, and 21 showed different results between species. Nevertheless, assimilation patterns were highly variable among Rhizopus oryzae isolates, and it was not possible to define a specific carbon assimilation profile. With both ID32C and API CH 50 strips, intraspecies variation was found to be low, while large differences were found between genera and species. The clustering of isolates based on their carbon assimilation profiles was in accordance with DNA-based phylogeny of Zygomycetes. In conclusion, carbon assimilation profiles allowed precise and accurate identification of most Zygomycetes to the species level.