[The strain differentiation of Candida albicans by morphotyping]

Morphotyping is a phenotypic method for strain differentiation of yeast cultures based on the comparison of appearance of their surfaces and fringes. For its simplicity and cost-effectiveness, it is recommended as an alternative tool to genotyping of Candida albicans. Our study aimed at verifying its usefulness for typing a group of C. albicans clinical isolates with emphasis on discrimination power. Prevalence of specific morphotypes in body locations with more tested isolates and according to age groups and gender of patients was also evaluated.

The tested group comprised 97 C. albicans isolates from 93 patients. With a cotton swab, 24-hour cultures were streaked onto malt extract agar. The surface and fringe morphology was assessed after 10-day incubation at 30 degrees C.

A total of 30 morphotypes were detected. The most frequent one had a code profile 7240 (n = 13, 13.4 %), followed by 5240 (n = 11) and 7340 (n = 9). The discrimination power calculated by Simpson's index of diversity reached 0.95. Results of reproducibility testing were identical in 54.6 % of isolates, another 36.1 % of isolates differed in one character. Some isolates (n = 35) were biotyped by our modification of Odds method. Using morphological criteria, 14 different phenotypes were defined, as opposed to 8 found by biotyping. Statistically significant differences were found when comparing morphotypes from the oropharynx, vagina and urine; the same was true for male and female morphotypes.

Our results clearly documented very good discrimination power of morphotyping for C. albicans isolates. This advantage as well as easiness to perform and low costs but markedly lower reproducibility in comparison with molecular genetic techniques makes it an optimal typing method for first-line use. Evaluation of morphological diversity of strains by this method can be further utilized in the studies of virulence, switching phenomenon or antifungal resistance.