Polyene susceptibility is dependent on nitrogen source in the opportunistic pathogen Candida albicans.
OBJECTIVE
Polyene antifungal drugs, including amphotericin B or nystatin, target ergosterol in the fungal plasma membrane and are used to treat systemic, vaginal and oral fungal infections. In the oral cavity, the available nitrogen sources are primarily in the form of proteins, which are poor nitrogen sources. This study evaluates the effect of protein as a nitrogen source on drug susceptibilities.


METHODS
Candida albicans was grown in protein [bovine serum albumin (BSA) or casein (CSN)] as a sole nitrogen source, in ammonium sulphate (AS) as a nitrogen source, or in both protein and AS.


RESULTS
Cells grown in BSA or CSN were 4- to 16-fold less susceptible to amphotericin B and nystatin than those grown in AS. Similar results were observed for cycloheximide, but not for fluconazole or caspofungin, and were observed for many C. albicans clinical isolates. The results were observed in two different media, and in broth and on agar. Cells grown under these nitrogen-poor conditions have a reduction in ergosterol sterol levels and a reduction in overall sterol synthesis. Quantitative real-time reverse transcription-polymerase chain reaction analysis shows that some genes involved in sterol biosynthesis are induced under nitrogen-limiting conditions, consistent with the lower sterol levels.


CONCLUSIONS
The results demonstrate that nitrogen source has a significant effect on polyene susceptibilities. As these nitrogen-limiting conditions mimic oral nitrogen availability, they suggest that in vitro polyene susceptibilities may overestimate the in vivo susceptibilities to polyene drugs in the mouth.
Oliver
Brian G
BG
Department of Pathobiology, School of Public Health and Community Medicine, University of Washington, Seattle, WA, USA.
Silver
Peter M
PM
White
Theodore C
TC
D000645:Ammonium Sulfate / Q000378:metabolism; D000666:Amphotericin B / Q000494:pharmacology; D000935:Antifungal Agents / Q000494:pharmacology*; D053898:Biosynthetic Pathways / Q000235:genetics; D002176:Candida albicans / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism*; D002364:Caseins / Q000378:metabolism; D003470:Culture Media / Q000737:chemistry; D003513:Cycloheximide / Q000494:pharmacology; D004875:Ergosterol / Q000032:analysis; D005656:Fungal Proteins / Q000096:biosynthesis / Q000235:genetics; D020869:Gene Expression Profiling; D006801:Humans; D008826:Microbial Sensitivity Tests; D009584:Nitrogen / Q000378:metabolism*; D009761:Nystatin / Q000494:pharmacology; D011090:Polyenes / Q000494:pharmacology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012710:Serum Albumin, Bovine / Q000378:metabolism; D015854:Up-Regulation
D000935:Antifungal Agents; D002364:Caseins; D003470:Culture Media; D005656:Fungal Proteins; D011090:Polyenes; D009761:Nystatin; D012710:Serum Albumin, Bovine; D000666:Amphotericin B; D003513:Cycloheximide; D009584:Nitrogen; D000645:Ammonium Sulfate; D004875:Ergosterol