Multilocus genotyping indicates that the ability to invade the bloodstream is widespread among Candida albicans isolates.

Multilocus genotyping was used to compare populations of Candida albicans from oral mucosa and blood. No significant differences in allele frequencies between the two samples were detected, and in a dendrogram of genotypic similarities, genotypes from both types of samples were finely interspersed. This is evidence for widespread distribution of invasive potential.

Evolution of drug resistance in experimental populations of Candida albicans.

Adaptation to inhibitory concentrations of the antifungal agent fluconazole was monitored in replicated experimental populations founded from a single, drug-sensitive cell of the yeast Candida albicans and reared over 330 generations. The concentration of fluconazole was maintained at twice the MIC in six populations; no fluconazole was added to another six populations. All six replicate populations grown with fluconazole adapted to the presence of drug as indicated by an increase in MIC; none of the six populations grown without fluconazole showed any change in MIC. In all populations evolved with drug, increased fluconazole resistance was accompanied by increased resistance to ketoconazole and itraconazole; these populations contained ergosterol in their cell membranes and were amphotericin sensitive. The increase in fluconazole MIC in the six populations evolved with drug followed different trajectories, and these populations achieved different levels of resistance, with distinct overexpression patterns of four genes involved in azole resistance: the ATP-binding cassette transporter genes, CDR1 and CDR2; the gene encoding the target enzyme of the azoles in the ergosterol biosynthetic pathway, ERG11; and the major facilitator gene, MDR1. Selective sweeps in these populations were accompanied by additional genomic changes with no known relationship to drug resistance: loss of heterozygosity in two of the five marker genes assayed and alterations in DNA fingerprints and electrophoretic karyotypes. These results show that chance, in the form of mutations that confer an adaptive advantage, is a determinant in the evolution of azole drug resistance in experimental populations of C. albicans.

Multilocus genotypes and DNA fingerprints Do not predict variation in azole resistance among clinical isolates of Candida albicans.

If variation in azole resistance is due to inherent differences in strains of Candida albicans, as a predominantly clonal organism, then correlation between multilocus genotypes and drug resistance would be expected. A sample of 81 clinical isolates from patients infected with human immunodeficiency virus in Toronto, Canada, plus 3 reference isolates were genotyped at 16 loci, distributed on all linkage groups, by means of oligonucleotide hybridizations specific for each of the alleles at each locus. These multilocus genotypes were significantly correlated with DNA fingerprints obtained with the species-specific probe 27A, indicating widespread linkage disequilibrium in the genome. There were 64 multilocus diploid genotypes and 77 DNA fingerprint types delineated in this sample. Neither the multilocus genotyping nor DNA fingerprinting alone identified all of the 81 types identified by the combination of these two methods. Multilocus genotypes were not predictive of fluconazole resistance, suggesting that resistance is gained or lost too quickly to be predicted by linkage with neutral markers.