Clonal and spontaneous origins of fluconazole resistance in Candida albicans

Abstract

The genotypes and susceptibilities to fluconazole of 78 strains of the human pathogenic yeast Candida albicans were compared. The strains comprised two sets of samples from Durham, N.C.: one from patients infected with the human immunodeficiency virus (HIV) and the other from healthy volunteers. For each strain, the MIC of fluconazole was determined by the standard National Committee for Clinical Laboratory Standards protocol. Genotypes were determined by PCR fingerprinting with five separate primers. The analysis revealed little evidence for genotypic clustering according to HIV status or body site. However, a small group of fluconazole-resistant strains isolated from patients infected with HIV formed a distinct cluster. In addition, two fluconazole-resistant strains were isolated from individuals who never took fluconazole, one from a patient infected with HIV and the other from a healthy person. The results suggest both clonal and spontaneous origins of fluconazole resistance in C. albicans.

FIG. 1

Examples of electrophoretic separation of PCR fingerprints obtained by amplifying genomic DNA from 34 strains of yeast isolated in this study using the M13 core sequence (5′-GAGGGTGGCCGGTTCT-3′) (A) and PA03 (5′-AGTCAGCCAC-3′) (B) as single primers. Lanes 1 and 36 are 1-kbp and 100-bp DNA ladders from GIBCO-BRL, respectively. Lanes 2 to 35 are strains in the following order: P6-vaginal, P7-oral, P8-rectal, P9-rectal, P10-rectal, P1-oral, P1-rectal, P11-oral, P11-vaginal, P11-rectal, P12-oral, P12-rectal, P2-oral, P3-oral, P14-oral, P4-oral, P4-rectal, P15-oral, P16-oral, P17-oral, P18-oral, P19-oral, P20-oral, P22-oral, P24-oral, P25-oral, P26-oral, P27-oral, P28-oral, P29-oral, P30-oral, P5-oral, P6-oral, and P21-oral.

FIG. 2

UPGMA phenogram of all 78 strains of C. albicans analyzed in this study. The strain names correspond to those in Table 1. Fluconazole-resistant strains are in boldface and underlined.

FIG. 3

UPGMA phenogram of the 38 strains of C. albicans from HIV-infected patients analyzed in this study. The strain names correspond to those in Table 1. Fluconazole-resistant strains are in boldface and underlined. The right-hand column indicates the MICs of fluconazole as determined by the NCCLS protocol.