Evaluation of the correlation of caspofungin MICs and treatment outcome in murine infections by wild type strains of Candida parapsilosis.

We have evaluated the in vitro activity of caspofungin against 36 wild-type strains of Candida parapsilosis sensu stricto using 3 techniques: broth microdilution, disk diffusion, and the determination of minimal fungicidal concentration (MFC). The first 2 methods showed a good in vitro activity of caspofungin, but the MFCs were ≥2 dilutions above their corresponding MICs. In a murine model of disseminated infection, we evaluated the efficacy of caspofungin at 5 mg/kg against 8 strains of C. parapsilosis representing different degrees of in vitro susceptibility (0.12-1 µg/mL). All the isolates responded to treatment and (1→3)-ß-D-glucan levels were reduced in all the cases; however, the study revealed differences among isolates, since caspofungin reduced the tissue burden of mice infected with isolates with MICs ≤0.5 µg/mL but was less effective against those with MICs of 1 µg/mL.

MIC values of voriconazole are predictive of treatment results in murine infections by Aspergillus terreus species complex.

We evaluated the efficacy of voriconazole against nine strains of Aspergillus terreus with different MICs (0.12 to 4 µg/ml) by using a murine model. Markers of efficacy included survival, tissue burden, galactomannan antigenemia, and drug serum levels. Voriconazole was especially effective in prolonging survival and reducing the fungal load in infections by strains that showed MICs that were less than or equal to the epidemiological cutoff value (1 µg/ml). In vitro data might be useful for predicting the outcome of A. terreus infections.

In vitro and in vivo activities of posaconazole and amphotericin B in a murine invasive infection by Mucor circinelloides: poor efficacy of posaconazole.

The in vitro susceptibility of 17 strains of Mucor circinelloides to amphotericin B and posaconazole was ascertained by using broth microdilution and disk diffusion methods and by determining the minimal fungicidal concentration (MFC). We evaluated the efficacy of posaconazole at 40 mg/kg of body weight/day and amphotericin B at 0.8 mg/kg/day in a neutropenic murine model of disseminated infection by M. circinelloides by using 6 different strains tested previously in vitro. In general, most of the posaconazole MICs were within the range of susceptibility or intermediate susceptibility, while the small inhibition zone diameters (IZDs) were indicative of nonsusceptibility for all isolates tested. The MFCs were ≥ 3 dilutions higher than the corresponding MICs. In contrast, amphotericin B showed good activity against all of the strains tested regardless of the method used. The in vivo studies demonstrated that amphotericin B was effective in prolonging survival and reducing the fungal load. Posaconazole showed poor in vivo efficacy with no correlation with the MIC values. The results suggested that posaconazole should be used with caution in the treatment of infections caused by Mucor circinelloides or by strains of Mucor not identified to the species level.

Studies on peptidyl nucleoside antibiotics: synthesis and antifungal evaluation of pyranosyl nucleoside analogs of nikkomycin.

BACKGROUND: The Streptomyces-derived nikkomycins are a unique class of peptidyl nucleoside natural products, with potent antifungal activity against a variety of pathogenic fungi. RESULTS: In continuation of our structure-activity relationship studies on the nikkomycins, this paper describes the strategic design, synthesis and biological evaluation of a 'doubly modified' generation of nikkomycin analogs. The structural modifications included a ring-expanded carbohydrate core and a simplified peptidyl side chain. Biological screening of these novel analogs against clinical isolates of various human pathogenic fungi indicated that the described modifications of the structural features of nikkomycin could be a potentially beneficial strategy towards optimizing the antifungal potency of this class of peptidyl nucleoside antibiotics. CONCLUSION: Continued investigation of the pyranosyl nikkomycin analogs is warranted to fully explore and optimize the structural features of this novel lead for the desired development of a new class of therapeutically useful antifungal drugs.

Evaluation of aminocandin and caspofungin against Candida glabrata including isolates with reduced caspofungin susceptibility.

BACKGROUND: Aminocandin is an investigational echinocandin with excellent activity against Candida species, including Candida albicans and Candida tropicalis. However, few data are available for this agent versus Candida glabrata. We compared the in vitro potency and in vivo efficacy of aminocandin and caspofungin against clinical isolates of C. glabrata including those with reduced caspofungin susceptibility (MIC > 2 mg/L). METHODS: In vitro activity was assessed using microdilution broth susceptibility testing. Three isolates, one with a low and two with elevated caspofungin MICs, were chosen and mice were infected with C. glabrata followed by a single dose of aminocandin or caspofungin (0.5-100 mg/kg), or daily doses of caspofungin (0.07-14.3 mg/kg) begun 1 day after inoculation. Reduction in fungal burden, assessed in kidney tissue on day 8 post-inoculation, was the marker of antifungal response. RESULTS: Aminocandin was more potent than caspofungin against each isolate with reduced caspofungin susceptibility. Mice infected with the caspofungin-susceptible isolate had significant decreases in tissue burden with low doses of either drug. Higher single doses of aminocandin (> or = 10 mg/kg) were required to reduce fungal burden against the two isolates with elevated caspofungin MICs. Single dose administration of caspofungin was ineffective against one of these isolates, and higher daily doses were required to reduce fungal burden. CONCLUSIONS: These studies suggest that aminocandin has the potential for extended interval dosing in the treatment of C. glabrata infections caused by susceptible isolates. However, higher doses may be required against isolates with reduced caspofungin susceptibility.

Infections caused by Scedosporium spp.

Scedosporium spp. are increasingly recognized as causes of resistant life-threatening infections in immunocompromised patients. Scedosporium spp. also cause a wide spectrum of conditions, including mycetoma, saprobic involvement and colonization of the airways, sinopulmonary infections, extrapulmonary localized infections, and disseminated infections. Invasive scedosporium infections are also associated with central nervous infection following near-drowning accidents. The most common sites of infection are the lungs, sinuses, bones, joints, eyes, and brain. Scedosporium apiospermum and Scedosporium prolificans are the two principal medically important species of this genus. Pseudallescheria boydii, the teleomorph of S. apiospermum, is recognized by the presence of cleistothecia. Recent advances in molecular taxonomy have advanced the understanding of the genus Scedosporium and have demonstrated a wider range of species than heretofore recognized. Studies of the pathogenesis of and immune response to Scedosporium spp. underscore the importance of innate host defenses in protection against these organisms. Microbiological diagnosis of Scedosporium spp. currently depends upon culture and morphological characterization. Molecular tools for clinical microbiological detection of Scedosporium spp. are currently investigational. Infections caused by S. apiospermum and P. boydii in patients and animals may respond to antifungal triazoles. By comparison, infections caused by S. prolificans seldom respond to medical therapy alone. Surgery and reversal of immunosuppression may be the only effective therapeutic options for infections caused by S. prolificans.

In vitro susceptibilities of 217 clinical isolates of zygomycetes to conventional and new antifungal agents.

We evaluated the in vitro susceptibilities of 217 zygomycetes to amphotericin B, ketoconazole, fluconazole, itraconazole, voriconazole, posaconazole, caspofungin, and flucytosine. The significant in vitro activity of posaconazole against several species appears to support its reported clinical efficacy. Decreased susceptibility to amphotericin B was noted with Cunninghamella bertholletiae.

Efficacy of caspofungin against Aspergillus terreus.

We investigated the in vitro and in vivo activities of caspofungin against Aspergillus terreus. The drug increased survival and reduced tissue fungal burden in neutropenic mice. Therefore, our data support the role of caspofungin in treating systemic infections due to this emerging pathogen.

Combination therapy with terbinafine and amphotericin B in a rabbit model of experimental invasive aspergillosis.

Antagonistic effects of combination therapy using amphotericin B (AmB) with agents which block ergosterol synthesis are a concern. Terbinafine was evaluated with AmB to assess antagonism or synergy in a rabbit model of invasive aspergillosis. Terbinafine had relatively little activity but did not demonstrate antagonism against AmB in our model.

Caspofungin in combination with amphotericin B against Candida glabrata.

The effects of caspofungin combined with amphotericin B were investigated with Candida glabrata. Although in vitro experiments showed an indifferent interaction, the combination regimen was the only therapeutic approach yielding organ sterilization in a murine candidemia model.

Scedosporium apiospermum soft tissue infection successfully treated with voriconazole: potential pitfalls in the transition from intravenous to oral therapy.

An immunocompromised patient with an invasive soft tissue infection due to Scedosporium apiospermum was successfully treated with voriconazole and surgical debridement. After transition from intravenous to oral therapy, successive adjustments of the oral dose were required to achieve complete resolution. For soft tissue infections due to molds characterized by thin, septate hyphae branching at acute angles, voriconazole should be considered a first-line antifungal agent. The potential usefulness of plasma voriconazole levels for guiding optimal therapy should be investigated.

Efficacies of amphotericin B (AMB) lipid complex, AMB colloidal dispersion, liposomal AMB, and conventional AMB in treatment of murine coccidioidomycosis.

The therapeutic efficacy of three lipid formulations of amphotericin B was compared with that of conventional amphotericin B in treatment of murine coccidioidomycosis. All treatments prolonged survival compared with the no-treatment group (P < 0.0001). Although conventional amphotericin B was more active than lipid formulations on reducing quantitative fungal load on a milligram-per-kilogram basis (P < 0.003 to 0.0002), the lipid preparations could be administered at higher doses, sterilizing liver and spleen tissues. The efficacies of the lipid preparations were similar in this murine model of coccidioidomycosis.

The role of antifungal susceptibility testing in the therapy of candidiasis.

Prior to the introduction of azoles, no real need for antifungal susceptibility testing (AFST) existed, as amphotericin B was the only agent available to treat systemic candidiasis. Introduction of fluconazole and itraconazole provided alternate, less toxic antifungal therapies. Intrinsic resistance of Candida krusei, decreased susceptibility of Candida glabrata, and development of resistance by Candida albicans (in mucosal disease in AIDS) to azoles led to development of our current AFST methodologies. The goal of AFST, like that of antibacterial susceptibility testing, is to predict clinical response, or at least to forecast failure. Although the ability of AFST to predict clinical outcome (clinical correlation) is still being fully elucidated, current methodologies do appear to reliably predict clinical resistance to azoles. Ready access to AFST is currently limited, affecting its timely use, but even with this lack of timeliness, AFST can still play an important role in patient care. Important potential roles include: 1) use in the development of local antibiograms to aid empiric selection of antifungals; 2) testing of isolates from candidemia or deep infection to aid in selection of long-term therapies; and, 3) the testing of isolates from recurrent mucosal disease to aid in selection of alternative regimens.

Experimental pulmonary aspergillosis due to Aspergillus terreus: pathogenesis and treatment of an emerging fungal pathogen resistant to amphotericin B.

Aspergillus terreus is an uncommon but emerging fungal pathogen, which causes lethal infections that are often refractory to amphotericin B (AmB). In comparison to Aspergillus fumigatus, A. terreus was resistant to the in vitro fungicidal effects of safely achievable concentrations of AmB. These in vitro findings correlated directly with resistance of A. terreus to AmB in experimental invasive pulmonary aspergillosis. Residual fungal pulmonary burden and galactomannan antigenemia demonstrated persistent infection, despite therapy with deoxycholate AmB or liposomal AmB. By comparison, posaconazole and itraconazole resolved GM antigenemia, reduced residual fungal burden, and improved survival. There were no differences in phagocytic host response to A. terreus versus A. fumigatus; however, the rate of conidial germination of A. terreus was slower. The strain of A. terreus with the highest minimum inhibitory and minimum lethal concentration of AmB also had the lowest membrane ergosterol content. The hyphae of A. terreus in vivo displayed distinctive aleurioconidia, which may be a practical microscopic feature for rapid preliminary diagnosis.

Candida glabrata oropharyngeal candidiasis in patients receiving radiation treatment for head and neck cancer.

Candida glabrata colonization is common in patients receiving radiation treatment for head and neck cancer, but to our knowledge has never been described as the infecting organism with oropharyngeal candidiasis (OPC). This study presents the first three patients described with C. glabrata OPC in this patient population. Patient 1 developed C. glabrata OPC and required fluconazole, 800 mg/day, for clinical resolution. Antifungal susceptibility testing revealed a MIC of fluconazole of >64 microg/ml. Elapsed time from initial culturing to treatment decision was 7 days. Patients 2 and 3 developed C. glabrata OPC. They were patients in a study evaluating OPC infections, and cultures were taken immediately. CHROMagar Candida plates with 0, 8, and 16 microg of fluconazole/ml were employed for these cultures. Lavender colonies, consistent with C. glabrata, grew on the 0- and 8-microg plates but not on the 16-microg plate from patient 2 and grew on all three plates from patient 3. Based on these data, a fluconazole dose of 200 mg/day was chosen for patient 2 and a dose of 400 mg/day was chosen for patient 3, with clinical resolution in both. Elapsed time from initial culturing to treatment decision was 2 days. C. glabrata does cause OPC in head and neck radiation treatment patients, and the use of fluconazole-impregnated chromogenic agar may significantly reduce treatment decision time compared to that with conventional culturing and antifungal susceptibility testing.