Daniela Arzeni

Effects of Caspofungin against Candida guilliermondii and Candida parapsilosis

ABSTRACT The in vitro activity of caspofungin (CAS) was investigated against 28 yeast isolates belonging to Candida albicans (n = 5), Candida guilliermondii (n = 10), and Candida parapsilosis (n = 13). CAS MICs obtained by broth dilution and Etest methods clearly showed a rank order of susceptibility to the echinocandin compound with C. albicans > C. parapsilosis > C. guilliermondii. Similarly, time-kill assays performed on selected isolates showed that CAS was fungistatic against C. albicans and C. parapsilosis, while it did not exert any activity against C. guilliermondii. In a murine model of systemic candidiasis, CAS given at doses as low as 1 mg/kg of body weight/day was effective at reducing the kidney burden of mice infected with either C. albicans or C. guilliermondii isolates. Depending on the isolate tested, mice infected with C. parapsilosis responded to CAS given at 1 and/or 5 mg/kg/day. However, the overall CFU reduction for C. guilliermondii and C. parapsilosis was approximately 100-fold less than that for C. albicans. Our study shows that CAS was active in experimental systemic candidiasis due to C. guilliermondii and C. parapsilosis, but this activity required relatively high drug dosages.

Interactions between Triazoles and Amphotericin B against Cryptococcus neoformans

ABSTRACT The interaction of amphotericin B (AmB) and azole antifungal agents in the treatment of fungal infections is still a controversial issue. A checkerboard titration broth microdilution-based method that adhered to the recommendations of the National Committee for Clinical Laboratory Standards was applied to study the in vitro interactions of AmB with fluconazole (FLC), itraconazole (ITC), and the new investigational triazole SCH 56592 (SCH) against 15 clinical isolates ofCryptococcus neoformans. Synergy, defined as a fractional inhibitory concentration (FIC) index of ≤0.50, was observed for 7% of the isolates in studies of the interactions of both FLC-AmB and ITC-AmB and for 33% of the isolates in studies of the SCH-AmB interactions; additivism (FICs, >0.50 to 1.0) was observed for 67, 73, and 53% of the isolates in studies of the FLC-AmB, ITC-AmB, and SCH-AmB interactions, respectively; indifference (FICs, >1.0 to ≤2.0) was observed for 26, 20, and 14% of the isolates in studies of the FLC-AmB, ITC-AmB, and SCH-AmB interactions, respectively. Antagonism (FIC >2.0) was not observed. When synergy was not achieved, there was still a decrease, although not as dramatic, in the MIC of one or both drugs when they were used in combination. To investigate the effects of FLC-AmB combination therapy in vivo, we established an experimental model of systemic cryptococcosis in BALB/c mice by intravenous injection of cells of C. neoformans 2337, a clinical isolate belonging to serotype D against which the combination of FLC and AmB yielded an additive interaction in vitro. Both survival and tissue burden studies showed that combination therapy was more effective than FLC alone and that combination therapy was at least as effective as AmB given as a single drug. On the other hand, when cells of C. neoformans 2337 were grown in FLC-containing medium, a pronounced increase in resistance to subsequent exposures to AmB was observed. In particular, killing experiments conducted with nonreplicating cells showed that preexposure to FLC abolished the fungicidal activity of the polyene. However, this apparent antagonism was not observed in vivo. Rather, when the two drugs were used sequentially for the treatment of systemic murine cryptococcosis, a reciprocal potentiation was often observed. Our study shows that (i) the combination of triazoles and AmB is significantly more active than either drug alone against C. neoformans in vitro and (ii) the concomitant or sequential use of FLC and AmB for the treatment of systemic murine cryptococcosis results in a positive interaction.

In Vitro Activities of the New Antifungal Triazole SCH 56592 against Common and Emerging Yeast Pathogens

ABSTRACT A broth microdilution method performed in accordance with the National Committee for Clinical Laboratory Standards guidelines was used to compare the in vitro activity of the new antifungal triazole SCH 56592 (SCH) to that of fluconazole (FLC), itraconazole (ITC), and ketoconazole (KETO) against 257 clinical yeast isolates. They included 220 isolates belonging to 12 different species of Candida, 15 isolates each of Cryptococcus neoformans andSaccharomyces cerevisiae, and seven isolates ofRhodotorula rubra. The MICs of SCH at which 50% (MIC50) and 90% (MIC90) of the isolates were inhibited were 0.06 and 2.0 μg/ml, respectively. In general, SCH was considerably more active than FLC (MIC50 and MIC90 of 1.0 and 64 μg/ml, respectively) and slightly more active than either ITC (MIC50 and MIC90 of 0.25 and 2.0 μg/ml, respectively) and KETO (MIC50 and MIC90 of 0.125 and 4.0 μg/ml, respectively). Our in vitro data suggest that SCH has significant potential for clinical development.

In Vitro Activity of Posaconazole against Clinical Isolates of Dermatophytes

ABSTRACT A broth macrodilution method following the recommendations established by the National Committee for Clinical Laboratory Standards was used to compare the in vitro activity of posaconazole (PCZ) with that of itraconazole (ITC) against 30 clinical isolates of dermatophytes belonging to six different species. In terms of MICs, PCZ showed an activity equal to that of ITC. MICs of PCZ at which 50% (MIC50) and 90% (MIC90) of the isolates were inhibited were 0.5 and >4.0 μg/ml, respectively. The MIC50 and MIC90 of ITC were 1.0 and >4.0 μg/ml, respectively. However, PCZ showed a more potent fungicidal activity than that of ITC against isolates belonging to the genus Microsporum (P = 0.03). PCZ merits further investigation as a potentially useful agent for treatment of dermatophytosis.

Comparison of the Fungicidal Activities of Caspofungin and Amphotericin B against Candida glabrata

ABSTRACT We investigated the fungicidal activity of caspofungin (CAS) and amphotericin B (AMB) against 16 clinical isolates of Candida glabrata. The minimum fungicidal concentrations (MFCs) of CAS were similar to those of AMB, ranging from 2.0 to >8.0 μg/ml. Time-kill assays performed on selected isolates showed that AMB was fungicidal at concentrations four times the MIC while CAS was not. A neutropenic-mouse model of disseminated infection was utilized to determine the residual fungal kidney burden. While doses as low as 0.3 and 1 mg/kg of body weight/day of CAS and AMB, respectively, were effective at reducing the counts with respect to controls, organ sterilization was reached when both drugs were administered at 5 mg/kg/day. Our study reveals that, similar to AMB, CAS has the potential for a fungicidal effect in vivo against this difficult-to-treat fungal pathogen.

Genotyping and antifungal susceptibility of human subgingival Candida albicans isolates

Subgingival colonization by Candida albicans has been described in human immunodeficiency virus (HIV)-infected individuals, but subgingival isolates have scarcely been characterized, particularly with respect to genotype and antifungal susceptibility. A series of 29 subgingival strains of C. albicans isolated from nine HIV-infected individuals was typed by electrophoretic karyotyping and tested for susceptibility to fluconazole, itraconazole, the new investigational triazole posaconazole and amphotericin B. DNA typing showed genetic heterogeneity within subgingival isolates, as almost every individual harbored his/her own specific isolate. Genetic identity was usually demonstrated within oral and subgingival isolates simultaneously collected from the same individual, but a number of DNA types were found to be unique to subgingival strains. These findings suggest that colonization is not just the result of Candida spreading from oral surfaces, and that subgingivally adapted strains could be involved. All isolates were susceptible to all the triazole drugs tested and amphotericin B. Additional studies on subgingival Candida colonization and further characterization of subgingival isolates are now required to clarify the role of Candida as opportunistic periodontal pathogen.

Prevalence and antifungal susceptibility of vaginal yeasts in outpatients attending a gynecological center in Ancona, Italy

Between February 1993 and May 1994 we studied the prevalence of fungal vulvovaginitis among women attending the Obstetric and Gynecology Clinic of the University of Ancona. Out of the 222 patients, 18 (8.2%) women had symptomatic vaginitis and 24 (10.8%) were carriers. Candida albicans was the species most frequently isolated (44.2%), followed by Torulopsis glabrata (28%) and Saccharomyces cerevisiae (16.2%), from symptomatic and carrier patients. The activity of acid proteinase was determined for C. albicans isolated from both symptomatic and carrier patients. All 13 carriers showed low activity for aspartyl proteinase (score 1+), while 5 of 6 symptomatic patients showed higher activity (score 2+), with a significant difference (p = 0.026). In general, isolates of T. glabrata and S. cerevisiae were less susceptible in vitro to fluconazole than isolates of C. albicans. We did not find any differences in fluconazole MIC results among the C. albicans strains isolated from symptomatic and carrier patients. On the other hand, the fluconazole MICs of T. glabrata and S. cerevisiae isolates showed statistically significant differences between symptomatic and carrier patients (p = 0.009 and p = 0.000, respectively). The differences in proteinase secretion between the isolates from symptomatic and carrier patients suggest a correlation between proteinase production and vaginal candidiasis caused by C. albicans. Torulopsis glabrata, however, was found to be the most common causative agent of vaginitis (7 out 19 episodes), followed by C. albicans (6 out of 19 episodes). Due to the varying patterns of antifungal susceptibility, mainly to fluconazole for the yeast isolates considered in this study, an in vitro susceptibility testing program might be useful for monitoring the outcome of this infection.

Genotypic identification of sequentialCandida albicans isolates from AIDS patients by polymerase chain reaction techniques

Random amplification of polymorphic DNA and inter-repeat polymerase chain reaction (IR-PCR) were compared with restriction fragment length polymorphism (RFLP) analysis as methods for DNA typing ofCandida albicans. Forty-seven strains ofCandida albicans isolated from the oral cavities of five AIDS patients undergoing fluconazole therapy were analyzed. There was an excellent correspondence between the DNA types obtained by both PCR-based techniques and by RFLP. With the exception of one patient who was infected with three DNA types ofCandida albicans during a five-year observation period, the patients each harboured only one major strain, which became progressively less susceptible to fluconazole. Each DNA type was unique to a patient. The data suggest that these typing methods are suitable for investigating the epidemiology of oropharyngeal candidiasis in this patient group.

Caspofungin in Combination with Amphotericin B against Candida glabrata

ABSTRACT 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.

In vitro susceptibility of dermatophytes to conventional and alternative antifungal agents

The minimum inhibitory concentrations (MICs), the minimal fungicidal concentrations (MFCs), the fungal biomass (FB) and hyphal viability employing the dye 3-4,5 dimethyl- 2-thiazolyl- 2,5- diphenyl- 2H tetrazolium bromide (MTT) were used to compare the in vitro effects of fluconazole (FLU) with those of the N-terminal palmitoyl-lipidated peptide, Pal-Lys-Lys-NH(2) (PAL), and a tea tree oil component, gamma-Terpinene (TER), against several clinical isolates of Microsporum canis and Trichophyton rubrum. In general, FLU and PAL MICs were significantly lower than those observed with TER, while no differences in the three drugs were found in the MFCs. However, they were from two to 16-times higher than their respective MICs. FB of M. canis treated with either FLU or PAL, but not with TER, was significantly reduced over untreated controls. Only PAL and TER, in a medium-dependent fashion, but not FLU, reduced the FB of T. rubrum. Finally, PAL was found to be significantly more active than FLU at reducing the hyphal viability against both genera of dermatophytes. This study shows that PAL exerts an in vitro activity against dermatophytes at least similar to that observed with FLU and suggests that this compound might be a promising candidate in the treatment of infections due to dermatophytes.