Impact of host factors on susceptibility to antifungal agents

An obstacle to drug development, particularly in this era of multiple drug resistance, is the under-appreciation for the role the host environment plays in microbial response to drugs. With the rise in fungal infection and drug resistance, particularly in individuals with co-morbidities, the influence serum and its components have on antimicrobial susceptibility requires assessment. This study examined the impact of physiologically relevant glucose and insulin levels in the presence and absence of 50 % human plasma on MICs for clinical isolates of Candida lusitaniae, Candida parapsilosis, Candida albicans, Candida tropicalis, Candida glabrata, Candida krusei and Cryptococcus neoformans. The addition of insulin or glucose at physiologic levels in RPMI medium alone altered the MIC in either a positive or negative fashion, depending on the organisms and drug tested, with C. glabrata most significantly altered with a 40, >32- and 46-fold increase in MIC for amphotericin B, itraconazole and miconazole, respectively. The addition of candida-antibody negative plasma also affected MIC, with the addition of glucose and insulin having a tandem effect on MIC. These findings indicate that phenotypic resistance of Candida and Cryptococcus can vary depending on the presence of insulin with glucose and plasma. This modulation of resistance may help explain treatment failures in the diabetic population and facilitate the development of stable drug-resistant strains. Furthermore, these findings indicate the need for a precision approach in the choice of drug treatment and drug development.