Evaluation of biotyping of medically important Candida spp

BACKGROUND: The biotyping system according to Odds and Abbott belongs to the most frequently used phenotypic methods. The aim of the study was to evaluate its discriminatory power in our laboratory. In addition, biotypes of isolates obtained from various body locations, present in defined age groups of patients and in males and females were also compared. MATERIAL AND METHODS: A total of 343 clinical isolates were typed belonging to six most frequent Candida spp. Nine types of tests for biotyping were prepared: sorbose, citrate and urea assimilation, tolerance to pH 1.4, pH 1.55 and higher concentration of NaCl, resistance to sodium periodate and boric acid and the ability to grow on MacConkey agar. RESULTS: Forty-one biotypes were found among 230 C. albicans isolates, nine among 21 C. glabrata, 13 among 25 C. parapsilosis, 12 among 25 C. krusei and five biotypes among 18 C. lusitaniae isolates. Contrary to other species, all of 18 C. tropicalis isolates belonged to the same biotype. In accordance with previously published reports, high discriminatory power of the method was found with Simpson's diversity index for C. albicans reaching 0.92. On the other hand, reproducibility was relatively low; from 12 randomly chosen C. albicans isolates tested repeatedly, only two showed identical results, five differed in one test and the others in several tests. Analysis of the occurrence of individual biotypes related to different anatomical locations, age groups and sexes of patients revealed neither statistically significant variations in distribution nor predilection of any single biotype. These findings suggest that the source of infection was endogenous in most cases. In comparison with results of similar studies, marked discrepancies in profiles of predominant biotypes were found, probably due to slight differences in composition of the test media or distinctive evaluation of results; however, it may reflect also geographical specificity of isolates. CONCLUSION: It can be concluded that the main advantages of the Odds biotyping system are high discriminatory power and cost-effectiveness. On the other hand, discrepancies in reproducibility of results as well as relatively long period for preparation of test media and for achieving of results decline its usefulness for epidemiological studies.