Evaluation of the new API 20C strip for yeast identification against a conventional method

Abstract

The new API 20C yeast identification system together with appropriate microscopic morphology determinations achieved a 97% correlation with a rapid conventional method. Whereas a group composed of Candida, Torulopsis, Saccharomyces and Rhodotorula was identified with ease (98% overall correlation), a 2nd group, containing Cryptococcus, Trichosporon and Geotrichum spp., appeared to give the system the most difficulty (90% correlation). Within this group particular difficulty was encountered in identifying varieties of Cryptococcus albidus, C. terreus, C. laurentii, Trichosporon beigelli and Geotrichum spp. as to species. The API 20C system should be incubated the full 72 h prescribed by the manufacturer. When used in conjunction with appropriate morphological tests, presumptive identifications of some Candida and Torulopsis spp. may be made at 24-48 h. To facilitate identifications of the more difficult group of yeasts, ancillary tests for determining nitrate reductase, urease and phenol oxidase activities should be considered as additions to the strip. Incorporating the phenol oxidase test would be especially important for identification of Cryptococcus neoformans, a yeast which should be identified as quickly and as accurately as possible. The API 20C system with computer assistance is an easy-to-inoculate, versatile and fairly rapid method of yeast identification, giving results comparable to those obtained by conventional methodologies.