Murine Model Of Systemic Candidiasis Research Articles

Microtiter broth dilution method for yeast susceptibility testing with validation by clinical outcome.

There is no ideal laboratory procedure or culture medium in current use for susceptibility testing of pathogenic yeasts. Six candidate growth media (RPMI 1640 with L-glutamine, yeast nitrogen base, Casamino Acids medium, Mueller-Hinton broth, Sabouraud dextrose broth, and minimum essential medium-Eagle salts) were screened by spectrophotometric absorbance for nucleic acid and protein. From these, two media were selected: a chemically defined growth medium (RPMI 1640 with L-glutamine) and a chemically complex medium (Casamino Acids). MICs of four antifungal agents (5-fluorocytosine, miconazole, ketoconazole, and amphotericin B) for 84 clinical isolates of various Candida species were then determined with both media in agar dilution and microtiter broth dilution systems. The resultant MICs were correlated with clinical outcome for those isolates obtained from patients treated with single antifungal agents, and susceptibility cut points were calculated. Derived MIC cut points for susceptibility were validated in a murine model of systemic candidiasis. RPMI 1640 with L-glutamine was found to have the lowest absorbance values for both nucleic acid and protein, while Casamino Acids medium was highest in both categories. We found that RPMI 1640 with L-glutamine was superior to Casamino Acids medium in the yield of MICs which correlated with actual clinical and animal outcome data. While there were no significant differences in MICs when RPMI 1640 medium was used, the microtiter broth dilution technique was superior to agar dilution in efficiency and ease of performance. We conclude that a microtiter broth system containing RPMI 1640 medium with L-glutamine is a simple, precise, and economical technique for susceptibility testing of pathogenic Candida species. We also suggest that the validation of susceptibility cut points with patient and animal outcome data make this microtiter broth system a preferential method for yeast susceptibility testing.

Interaction of rifampin with other antifungal agents in experimental murine candidiasis.

A murine model of systemic candidiasis was used for evaluation of the interaction of rifampin with ketoconazole and amphotericin B. In vitro studies with a clinical isolate of Candida albicans showed that rifampin modestly potentiated the antifungal activity of both of these drugs. When mice were challenged iv with C. albicans, therapy with rifampin plus ketoconazole or rifampin plus amphotericin B significantly reduced counts in kidney tissue from levels in untreated controls. However, rifampin plus amphotericin B was no more effective than amphotericin B alone, and rifampin plus ketoconazole was no more effective than ketoconazole alone. In challenges with lethal numbers of organisms, amphotericin B or ketoconazole alone increased the rate of survival from 0% to approximately 50%, and the addition of rifampin to the regimen conferred no further benefit. Therefore, the use of rifampin with either of these antifungal agents resulted in minimal, if any, increase in efficacy.