Change in fluconazole susceptibility patterns and genetic relationship among oral Candida albicans isolates

To assess the genetic homogeneity or heterogeneity within each set of Candida albicans isolates colonizing/infecting the oral cavities of HIV-infected patients undergoing azole therapy when changes in susceptibility to fluconazole were detected.

Fourteen HIV-positive patients suffering recurrent episodes of oral candidosis were prospectively followed from the first episode to the isolation of strains with decreased susceptibility to fluconazole. The strains of C. albicans isolated either from episodes or controls throughout the prospective study were analysed.

Electrophoretic karyotyping and hybridization with the repeated sequence probe 27A were used to delineate sequential isolates. In vitro susceptibility tests to fluconazole and ketoconazole were also performed. The results obtained by DNA fingerprinting with the probe combined with computer-assisted analysis were used to assess the genetic relationships amongst the strains. In addition, comparison with the genetic relatedness of a group of geographically unrelated strains was made.

Isogenic populations of sequential isolates were observed only in two patients; 12 patients harboured heterogenic populations over time, although in 11 patients there was a predominant strain that was isolated more than once, and only one of these patients carried strains with a similarity index less than 80%. With the exception of two patients, each patient carried a major strain that became less susceptible to fluconazole. The similarity index for the unrelated strains was 59%.

HIV-infected patients may carry a mixed population of strains, but the strains tend to be related to each other. The strains were maintained throughout the course of infection and at least one developed secondary resistance to fluconazole.