Tolerance to amphotericin B in clinical isolates of Candida tropicalis.

A broth microdilution method was used for testing amphotericin B against 33 clinical isolates of Candida tropicalis. All isolates were in vitro susceptible to the polyene (MIC [minimal inhibitory concentration] < or = 1.0 microg/mL). However, when the isolates were cultured in a medium containing amphotericin B at a concentration of 1.5 microg/mL, a wide interstrain variation of growth rate was observed. Five isolates (15%) proved to be highly tolerant to the drug and grew at a frequency ranging from 1 x 10(-1) to 2 x 10(-2). Twenty-three isolates (70%) grew at a frequency ranging from 1 x 10(-5) to 1 x 10(-8). The remaining five isolates (15%) failed to grow in drug-containing medium. In general, this growth variation was not associated with amphotericin B MICs displayed by the single isolates. In addition, the strains grown in drug-containing medium did not represent amphotericin B-resistant mutants, as shown by the maintenance of MICs similar to those of their respective parent isolates. Killing experiments conducted in selected isolates confirmed a variation of fungicidal activity of amphotericin B. To see whether this phenomenon was associated with a variation of amphotericin B response in vivo, we established an experimental model of systemic murine candidiasis in CD1 mice by intravenous injection of cells belonging to Candida tropicalis 3147 (growth rate at a frequency of 1 x 10(-1) in amphotericin B medium) and Candida tropicalis 4055 (no growth). Low (0.3 mg/kg/day) and high (1 mg/kg/day) doses of amphotericin B were both effective at reducing the fungal burdens in the kidneys of mice infected with either strain (p, 0.01 to 0.02). However, whereas the burden of mice infected with isolate 3147 and treated with the polyene at 0.3 mg/kg/day was reduced by 1.2 +/- 0.25 (mean +/- standard deviation) log10 cfu/g compared to untreated mice, the same dosing regimen yielded a burden reduction of 2.6 +/- 0.07 log10 cfu/g in mice infected with isolate 4055 (p < 0.001). Similarly, amphotericin B at 1 mg/kg/day yielded a burden reduction of 1.8 +/- 0.20 vs. 2.5 +/- 0.30 log10 cfu/g in mice infected with isolates 3147 and 4055, respectively (p < 0.001). Our data revealed a variable pattern of tolerance to amphotericin B among isolates of Candida tropicalis and showed that this phenomenon might influence the rate of organ clearance during therapy.

Sequential therapy with caspofungin and fluconazole for Candida albicans infection.

A sequential therapy of caspofungin (CAS) and fluconazole (FLC) administration for treatment of Candida albicans infection was investigated. Treatment with CAS followed by FLC was as effective as CAS treatment given alone for the same duration. Our data suggest that switching from CAS to FLC is a potentially explorable therapeutic option for treatment of systemic candidiasis.

In vitro activities of voriconazole in combination with three other antifungal agents against Candida glabrata.

Candida glabrata has recently emerged as a significant pathogen involved in both superficial and deep-seated infections. In the present study, a checkerboard broth microdilution method was performed to investigate the in vitro activities of voriconazole (VOR) in combination with terbinafine (TRB), amphotericin B (AMB), and flucytosine (5FC) against 20 clinical isolates of C. glabrata. Synergy, defined as a fractional inhibitory concentration (FIC) index of < or = 0.50, was observed in 75% of VOR-TRB, 10% of VOR-AMB, and 5% of VOR-5FC interactions. None of these combinations yielded antagonistic interactions (FIC index > 4). When synergy was not achieved, there was still a decrease in the MIC of one or both drugs used in the combination. In particular, the MICs were reduced to < or = 1.0 microg/ml as a result of the combination for all isolates for which the AMB MIC at the baseline was > or = 2.0 microg/ml. By a disk diffusion assay, the halo diameters produced by antifungal agents in combination were greater that those produced by each drug alone. Finally, killing curves showed that VOR-AMB exhibited synergistic interactions, while VOR-5FC sustained fungicidal activities against C. glabrata. These studies demonstrate that the in vitro activity of VOR against this important yeast pathogen can be enhanced upon combination with other drugs that have different modes of action or that target a different step in the ergosterol pathway. Further studies are warranted to elucidate the potential beneficial effects of such combination regimens in vivo.

Point prevalence, microbiology and fluconazole susceptibility patterns of yeast isolates colonizing the oral cavities of HIV-infected patients in the era of highly active antiretroviral therapy.

We conducted a prospective study to address the prevalence and microbiological characteristics of yeast isolates colonizing the oral cavities of HIV-infected patients undergoing highly active antiretroviral therapy. Sixty-eight patients (67%) from a total of 102 were found to be colonized with yeasts. Sixty-five patients carried a single species (60 Candida albicans, three Candida glabrata and two Candida krusei) and three patients had mixed colonization of C. albicans and C. krusei. The status of yeast carrier was not associated with the number of CD4 cells or the viral load. Similarly, the type of antiretroviral regimen was not associated with the carriage of Candida spp. The only predictor of Candida colonization was a previous history of oropharyngeal candidiasis (P = 0.009). Although many patients in this series had already been treated with repeated courses of fluconazole therapy for previous episodes of oropharyngeal candidiasis, fluconazole susceptibility patterns showed that 93% of yeasts were susceptible to this triazole in vitro (MIC < or = 8.0 mg/L).