[Study of mycological examination methods in clinical laboratories--specimen pretreatment and isolation].

ABSTRACT

We performed a comparative study of the effects of centrifugation, large amounts of inoculum and incubation temperature with regard to recovery of Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus from fungal suspensions in order to identify optimal processing methods for mycological examination of clinical specimens. The number of fungal colonies, except for Candida spp., isolated from respiratory specimens, and the duration of incubation needed to isolate pathogenic fungi from clinical specimens were also analyzed retrospectively. There was a difference in the number of recovered colonies, with or without centrifugation, between inoculum sizes of 10 microl and 50 microl, but no differences were observed in the results obtained under two sets of centrifugation conditions 2,000 x g for 15 minutes and 3,000 x g for 20 minutes. Candida albicans and Aspergillus fumigatus developed more rapidly at 35 degrees C than at 27 degrees C in the first 24 hours of incubation, while Cryptococcus neoformans formed a larger colony at 27 degrees C than at 35 degrees C. One to three colonies of Aspergillus spp. and Cryptococcus spp. were isolated from respiratory specimens in 73% and 50% of cases, respectively. The required incubation period was six days for isolation of 65 Aspergillus spp. strains from respiratory specimens, while 14 days was needed for isolation of 46 dermatophyte strains. Based on these results, we recommend a pretreatment of centrifugation and a large quantity of inoculum for respiratory specimen processing, as well as an incubation period of at least 7 days and 21 days for internal and dermatological specimens, respectively.