In vivo development of fluconazole resistance in serial Cryptococcus gattii isolates from a cat.
Elevated fluconazole minimum inhibitory concentrations (MICs) are more frequently observed in Cryptococcus gattii compared to C. neoformans isolates; however, the development of in vivo resistance and the molecular mechanisms responsible have not been reported for this species. We report a case of Cryptococcus gattii (molecular type VGIII) that developed reduced susceptibility to fluconazole during therapy and delineate the molecular mechanisms responsible. Multilocus sequence typing and quantitative DNA analysis of the pre- and post-treatment isolates was performed using well-characterized methods. Pre- and post-treatment clinical isolates were confirmed isogenic, and no differences in ERG11 or PDR11 sequences were found. qPCR found an overexpression of ERG11 and the efflux pump PDR11 in the resistant isolate compared to the isolate collected prior to initiation of antifungal therapy. Reversion to wild-type susceptibility was observed when maintained in antifungal-free media confirming the in vivo development of heteroresistance. The in vivo development of heteroresistance to fluconazole in our patient with C. gattii is secondary to overexpression of the efflux pump PDR11 and the drug target ERG11. Additional work in other clinical isolates with elevated fluconazole MICs is warranted to evaluate the frequency of heteroresistance versus point mutations as a cause of resistance.
Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis.
Jane E
JE
Sykes
Department of Medical Microbiology and Immunology, One Shields Avenue, Tupper Hall, University of California, Davis.
Greg
G
Hodge
Department of Medical Microbiology and Immunology, One Shields Avenue, Tupper Hall, University of California, Davis.
Anil
A
Singapuri
Department of Medical Microbiology and Immunology, One Shields Avenue, Tupper Hall, University of California, Davis.
Mai Lee
ML
Yang
Department of Pharmacology, School of Medicine, University of California, Davis, California.
Angie
A
Gelli
Department of Medical Microbiology and Immunology, One Shields Avenue, Tupper Hall, University of California, Davis.|Department of Internal Medicine, Division of Infectious Diseases, University of California Davis Medical Center, 4150 V Street, Suite G500; University of California, Davis.
George R
GR
Thompson
D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology* / Q000627:therapeutic use*; D002415:Cats; D003453:Cryptococcosis / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary*; D056285:Cryptococcus gattii / Q000187:drug effects* / Q000302:isolation & purification; D025141:Drug Resistance, Fungal; D005260:Female; D015725:Fluconazole / Q000494:pharmacology* / Q000627:therapeutic use*; D005656:Fungal Proteins / Q000235:genetics; D020869:Gene Expression Profiling; D005838:Genotype; D008826:Microbial Sensitivity Tests; D058889:Molecular Typing; D016533:Mycological Typing Techniques; D060888:Real-Time Polymerase Chain Reaction
D000935:Antifungal Agents; D005656:Fungal Proteins; D015725:Fluconazole
Cryptococcus gattii; VGIII; fluconazole; heteroresistance; in vivo; resistance; triazole