Surveillance of antifungal susceptibilities in clinical isolates of Candida species at 36 hospitals in China from 2009 to 2013

BACKGROUND

The purpose of this study was to determine the species distribution and to monitor the antifungal susceptibility profiles of clinical Candida isolates collected in China from 2009 to 2013.

METHODS

The antifungal susceptibilities of 952 Candida isolates were tested.

RESULTS

Candida albicans was the most common species, accounting for 65.7% of the total isolates. The most frequently isolated non-albicans Candida species in this study was Candida glabrata (193, 20.3%). Nearly 7.6%, 3.2%, 1.8%, and 1.1% of the 952 isolates exhibited decreased susceptibility to fluconazole, voriconazole, itraconazole, and flucytosine, respectively. Moreover, seven C. albicans and one Candida krusei had an amphotericin B minimum inhibitory concentration (MIC) of 2 μg/ml.

CONCLUSIONS

The distribution of species and the prevalence of antifungal resistance in Candida isolates varied among different areas in China. Continuous monitoring of resistance patterns is necessary to control the spread of resistance in clinical isolates of Candida species.

Antifungal drug resistance in Candida species

Invasive Candida infections are well established infectious entities of immunocompromised or critically ill patients and are characterised by high morbidity and mortality. Owing to the common eukaryotic structure of fungi and humans, a limited number of antifungal drugs is available for therapeutic purposes. In this unsatisfactory scenario, the emergence of drug resistance represents an important health problem. Failure of antifungal treatment can be related to host factors, to the pharmacokinetic and pharmacodynamic parameters of the drug, or to morphological, reproductive modalities and biofilm production of the fungus itself. Innate or acquired antifungal resistance derives from the presence or onset of molecular mechanisms related to the toxic activity of the drug itself. The resulting resistance can thus be extended to different molecules of the same class according to a greater or lesser affinity of the molecules for the target. In addition, non-specific cellular mechanisms of extrusion of toxic substances, such as overexpression of efflux pumps, can play a role involving different antifungal classes. Here we briefly review the current antifungal susceptibility testing methods and their usefulness as predictors of antifungal resistance in Candida spp., focusing on assessment of the involved molecular mechanisms.

The synthesis and activities of novel mononuclear or dinuclear cyclen complexes bearing azole pendants as antibacterial and antifungal agents

A series of novel compounds containing 1,4,7,10-tetraazacyclododecane and azoles were synthesized and characterized by (1)H NMR, MS and elemental analysis. Bioactive assay manifested that some target compounds, such as 11a, 11b and 11d, displayed good and broad spectrum antimicrobial activities with relative low MIC values against most of tested strains. These dinuclear complexes gave comparable or even better antimicrobial efficiencies than the reference drugs Fluconazole and Chloromycin. The result showed that the metal ions were the key factors to enhance the antimicrobial activities for mononuclear or dinuclear complexed in varying degrees. The interaction evaluation of compound 11b with bovine serum albumin (BSA) as an example was tested by fluorescence method. The thermodynamic parameters indicated that the hydrogen bonds and van der waals forces played the major roles in the strong association between dinuclear compound and BSA. The CCK-8 tests also confirmed the safeties of these dinuclear compounds in vitro.

Voriconazole pharmacokinetics and exposure-response relationships: assessing the links between exposure, efficacy and toxicity

The triazole antifungal voriconazole (VCZ) exhibits broad-spectrum antifungal activity and is the first-line treatment for invasive aspergillosis. Highly variable, non-linear pharmacokinetics, metabolism via the polymorphic drug-metabolising enzyme CYP2C19, and a range of serious adverse events (AEs) including hepatotoxicity and neurotoxicity complicate the clinical utility of VCZ. As interest in optimising VCZ treatment has increased, a growing number of studies have examined the relationships between VCZ exposure and efficacy in the treatment and prevention of invasive fungal infections, as well as associations with VCZ-related AEs. This review provides a critical analysis of VCZ pharmacokinetics and exposure-response (E-R) relationships, assessing the links between VCZ exposure, efficacy and toxicity. Low VCZ exposure has frequently been associated with a higher incidence of treatment failure; fewer studies have addressed E-R relationships with prophylactic VCZ. VCZ-related neurotoxicity appears common at high VCZ concentrations and can be minimised by maintaining concentrations below the recommended upper concentration thresholds; hepatotoxicity appears to be associated with increased VCZ exposure but is also prevalent at low concentrations. Further research should aim to inform and optimise the narrow therapeutic range of VCZ as well as develop interventions to individualise VCZ dosing to achieve maximal efficacy with minimal toxicity.

The impact of new epidemiological cutoff values on Candida glabrata resistance rates and concordance between testing methods

Interpretive criteria for Candida susceptibility testing were recently revised with the establishment of species-specific epidemiological cutoff values (ECV). To assess the effect of modified cutoff values on Candida glabrata resistance rates and agreement between testing methods, we tested the susceptibility of 598 clinical isolates to fluconazole, itraconazole, voriconazole, posaconazole, caspofungin, and amphotericin B using CLSI M27-A3 and E-test methods. The caspofungin MICs clustered above the ECV and below the CLSI cutoff (MIC50, 0.5 μg/mL). Applying the ECV reduced the proportion of itraconazole-nonsusceptible strains from 83% to 0.3% but minimally affected resistance rates of other drugs. Categorical agreement between broth microdilution and E-test was increased for itraconazole and reduced for voriconazole and caspofungin. The current caspofungin ECV may not reproducibly differentiate resistant and susceptible C. glabrata strains in hospitals with varying MIC distributions.

and triazoles against Aspergillus spp

Candida and Aspergillus infections have emerged as significant pathogens in recent decades. During this same time, broad spectrum triazole and echinocandin antifungal agents have been developed and increasingly used. One consequence of widespread use is leading to the emergence of mutants with acquired resistance mutations. Therefore, accurate susceptibility testing and appropriate clinical breakpoints for the interpretation of susceptibility results have become increasingly important. Here we review the underlying methodology by which breakpoints have been selected by EUCAST (European Committee on Antimicrobial Susceptibility Testing). Five parameters are evaluated: dosing regimens used; EUCAST MIC distributions from multiple laboratories, species and compound specific epidemiological cut off values (upper MIC limits of wild type isolates or ECOFFs), pharmacokinetic/pharmacodynamic relationships and targets associated with outcome and finally clinical data by species and MIC when available. The general principles are reviewed followed by a detailed review of the individual aspects for Candida species and the three echinocandins and for Aspergillus and the three mould-active azoles. This review provides an update of the subcommittee on antifungal susceptibility testing (AFST) of the EUCAST methodology and summarises the current EUCAST breakpoints for Candida and Aspergillus. Recommendations about applicability of antifungal susceptibility testing in the routine setting are also included.

Cyclosporine/ketoconazole reduces treatment costs for nephrotic syndrome

Cyclosporine A (CyA) is an effective agent for the treatment of glucocorticoid-dependent idiopathic nephrotic syndrome (GCDNS), but costs are prohibitive in resource-poor societies. The objectives of this study were to evaluate the efficacy and safety of reducing the dose of CyA by co-administering ketoconazole. A prospective study targeting children 2-18 years of age with GCDNS in remission with CyA monotherapy was conducted. CyA dose was reduced by 50% and ketoconazole was added at 25% of the recommended therapeutic dose, and the drug levels and therapeutic and adverse effects (AE) were monitored. Continued combined therapy after completion of the 4-week trial period was offered. Ten patients (median age 9.5 years, range 3.0-16.0 years) were enrolled in the study. At week 4, the CyA dose was 2.2 ± 0.7 mg/kg/day compared with 5.6 ± 0.9 mg/kg/day at enrolment (P < 0.0001). No AE were noted. All patients continued ketoconazole treatment for at least 3 months. CyA drug cost savings were 61%, and approximately 60% with ketoconazole cost included. The combination of an expensive immunosuppressive drug with a cheap metabolic inhibitor reduced the treatment costs by> 50% without increased adverse events or drug monitoring needs. This intervention demonstrates how access of patients with limited resources to needed drugs can be improved by interference with physiological drug elimination.

Efficacy of some synthesized thiazoles against dermatophytes

Twelve thiazoles and their fused derivatives were tested for their antimicrobial activity against Trichophyton rubrum, T. terrestre, Epidermophyton floccosum, and Microsporum gypseum. Most of the synthesized compounds were inhibitory to the tested fungi. The most effective compound was 5-(4-ethoxybenzylidene-4,5-dihydro-4-oxothiazol-2-yl)-N,3-diphenylbut-2-namide (3c) followed by 2-(4-oxo-4,5-dihydrothiazol-2-yl)-3-phenyl-but-2-enoic acid-(3-cyano-4,5,6,7-tetrahydrobenzo[b]thiophen-2-yl)-amide (2b). These compounds were more efficacious than terbinafine, the reference drug. The tested compounds caused variable reduction in the activity of keratinase of the dermatophytes, depending on the azole derivative and the test fungus. Thiazole derivatives (2b) and (3c) exhibited the highest efficacy in decreasing ergosterol biosynthesis of the tested dermatophytes. The treatment of guinea pigs with compound (3c) induced complete curing in the case of all the test dermatophytes 30days post-treatment. The percent curing for compounds (3c) and (2b) was better than the reference drug.

Insight into pleiotropic drug resistance ATP-binding cassette pump drug transport through mutagenesis of Cdr1p transmembrane domains

The fungal ATP-binding cassette (ABC) transporter Cdr1 protein (Cdr1p), responsible for clinically significant drug resistance, is composed of two transmembrane domains (TMDs) and two nucleotide binding domains (NBDs). We have probed the nature of the drug binding pocket by performing systematic mutagenesis of the primary sequences of the 12 transmembrane segments (TMSs) found in the TMDs. All mutated proteins were expressed equally well and localized properly at the plasma membrane in the heterologous host Saccharomyces cerevisiae, but some variants differed significantly in efflux activity, substrate specificity, and coupled ATPase activity. Replacement of the majority of the amino acid residues with alanine or glycine yielded neutral mutations, but about 42% of the variants lost resistance to drug efflux substrates completely or selectively. A predicted three-dimensional homology model shows that all the TMSs, apart from TMS4 and TMS10, interact directly with the drug-binding cavity in both the open and closed Cdr1p conformations. However, TMS4 and TMS10 mutations can also induce total or selective drug susceptibility. Functional data and homology modeling assisted identification of critical amino acids within a drug-binding cavity that, upon mutation, abolished resistance to all drugs tested singly or in combinations. The open and closed Cdr1p models enabled the identification of amino acid residues that bordered a drug-binding cavity dominated by hydrophobic residues. The disposition of TMD residues with differential effects on drug binding and transport are consistent with a large polyspecific drug binding pocket in this yeast multidrug transporter.

Current treatment options for invasive aspergillosis

Invasive pulmonary aspergillosis is a major cause of morbidity and mortality in immunocompromised patients, particularly those with hematological malignancies in the setting of profound neutropenia and/or hematopoietic stem cell transplant recipients. The optimal therapy for invasive aspergillosis relies on the restoration of leukocyte counts and effective antifungal treatment initiated at the earliest stage of infection. Several alternative antifungal compounds are currently available. A rational approach should take into account not only the degree of certainty of infection (as codified by the EORTC/MSG classification), but also previous exposure to other antifungals, the pharmacokinetic and pharmacodynamic characteristics of the antifungals employed and the clinical characteristics of the patient.