Evaluation of antifungal susceptibility testing with microdilution and Etest methods of Candida blood isolates

Species Distribution, Antifungal Susceptibility, and Molecular Epidemiology of Candida Species Causing Candidemia in a Tertiary Care Hospital in Bangkok, Thailand

Candida species represent a common cause of bloodstream infection (BSI). Given the emergence of non-albicans Candida (NAC) associated with treatment failure, investigations into the species distribution, fungal susceptibility profile, and molecular epidemiology of pathogens are necessary to optimize the treatment of candidemia and explore the transmission of drug resistance for control management. This study evaluated the prevalence, antifungal susceptibility, and molecular characteristics of Candida species causing BSI in a tertiary-level hospital in Bangkok, Thailand. In total, 54 Candida isolates were recovered from 49 patients with candidemia. C. tropicalis was the most prevalent species (33.3%), followed by C. albicans (29.6%). Most Candida species were susceptible to various antifungal agents, excluding C. glabrata and C. tropicalis, which had increased rates of non-susceptibility to azoles. Most C. glabrata isolates were non-susceptible to echinocandins, especially caspofungin. The population structure of C. albicans was highly diverse, with clade 17 predominance. GoeBURST analysis of C. tropicalis revealed associations between genotype and fluconazole resistance in a particular clonal complex. The population structure of C. glabrata appeared to have a low level of genetic diversity in MLST loci. Collectively, these data might provide a fundamental database contributing to the development of novel antifungal agents and diagnostic tests.

Change in species distribution and antifungal susceptibility of candidemias in an intensive care unit of a university hospital (10-year experience)

Candidemia is a nosocomial infection mostly found in critically ill patients. Our objectives were to evaluate the change in distribution and resistance profile of Candida spp. isolated from candidemic patients in our intensive care unit over two 5-year periods spanning 15 years and to evaluate the risk factors. Records from the microbiology laboratory were obtained, from January 2004 to December 2008 and from January 2013 to December 2017, retrospectively. Antifungal susceptibility was performed by E-test and evaluated according to EUCAST breakpoints. A total of 210 candidemia cases occurred; 238 Candida spp. were isolated in 197 patients (58.8% male; mean age, 59.2 ± 19.6 years). The most predominant risk factor was central venous catheter use. Species distribution rates were 32%, 28%, 17%, and 11% for C. albicans (n = 76), C. parapsilosis (n = 67), C. glabrata (n = 40), and C. tropicalis (n = 27), respectively. Resistance rate to anidulafungin was high in C. parapsilosis over both periods and increased to 73% in the second period. Fluconazole showed a remarkable decrease for susceptibility in C. parapsilosis (94 to 49%). The prevalence of MDR C. parapsilosis (6%/33%) and C. glabrata (0%/44%) increased in the second period. We observed a predominance of non-albicans Candida spp., with C. parapsilosis being the most frequent and C. glabrata infections presenting with the highest mortality. High level of echinocandin resistance in C. parapsilosis and increasing prevalences of MDR C. parapsilosis and C. glabrata seem emerging challenges in our institution.

Synthesis, structural characterization, and prospects for new cobalt (II) complexes with thiocarbamoyl-pyrazoline ligands as promising antifungal agents

Candida spp. cause invasive fungal infections. One species, Candida glabrata, may present intrinsic resistance to conventional antifungal agents, thereby increasing mortality rates in hospitalized patients. In this context, metal complexes present an alternative for the development of new antifungal drugs owing to their biological and pharmacological activities demonstrated in studies in the last decades. Accordingly, in this study we have synthesized and characterized two new Co(II) complexes with thiocarbamoyl-pyrazoline ligands to assess their antimicrobial, mutagenic, and cytotoxic potential. For antimicrobial activity, the broth microdilution method was performed against ATCC strains of Candida spp. and fluconazole dose-dependent isolates of C. glabrata obtained from urine samples. The Ames test was used to assess mutagenic potential. The reduction method of the MTS reagent (3 [4,5-dimethylthiazol-2-yl]-5-[3-carboxymethoxyphenyl]-2-[4-sulfophenyl]-2H-tetrazolium) was performed with HeLa, SiHa, and Vero cells to determine cytotoxicity. Both complexes exhibited fungistatic and fungicidal activity for the yeasts used in the study, demonstrating greater potential for C. glabrata ATCC 2001 and the C. glabrata CG66 isolate with a Minimum Inhibitory Concentration MIC from 3.90 to 7.81 μg mL^-1 and fungicidal action from 7.81 to 15.62 μg mL^-1. The complexes inhibited and degraded biofilms by up to 90% and did not present mutagenic and cytotoxic potential at the concentrations evaluated for MIC. Thus, the complexes examined herein suggest promising alternatives for the development of new antifungal drugs.

Antifungal Susceptibly Testing by Concentration Gradient Strip Etest Method for Fungal Isolates: A Review

Antifungal susceptibility testing is an important tool for managing patients with invasive fungal infections, as well as for epidemiological surveillance of emerging resistance. For routine testing in clinical microbiology laboratories, ready-to-use commercial methods are more practical than homemade reference techniques. Among commercially available methods, the concentration gradient Etest strip technique is widely used. It combines an agar-based diffusion method with a dilution method that determinates a minimal inhibitory concentration (MIC) in µg/mL. Many studies have evaluated the agreement between the gradient strip method and the reference methods for both yeasts and filamentous fungi. This agreement has been variable depending on the antifungal, the species, and the incubation time. It has also been shown that the gradient strip method could be a valuable alternative for detection of emerging resistance (non-wild-type isolates) as Etest epidemiological cutoff values have been recently defined for several drug-species combinations. Furthermore, the Etest could be useful for direct antifungal susceptibility testing on blood samples and basic research studies (e.g., the evaluation of the in vitro activity of antifungal combinations). This review summarizes the available data on the performance and potential use of the gradient strip method.

The Etest Performed Directly on Blood Culture Bottles Is a Reliable Tool for Detection of Fluconazole-Resistant Candida albicans Isolates

We assessed the ability of the Etest performed directly on positive blood cultures (ET_DIR) to detect fluconazole susceptibility in 6 fluconazole-resistant and 12 fluconazole-susceptible Candida albicans isolates, according to CLSI M27-A3 and EUCAST EDef 7.2 procedures. Categorical agreement between ET_DIR and broth microdilution was 100% when the trays were incubated at 25°C and trailing effect was ruled out. ET_DIR is a reliable procedure when screening for the presence of fluconazole resistance in C. albicans.

Identification and antifungal susceptibility of Candida species isolated from bloodstream infections in Konya, Turkey

Background

In this study, our aim was to identify Candida species isolated from bloodstream infections and to determine their susceptibilities to various antifungal agents to demonstrate the local resistance profiles and to guide empirical treatment for clinicians.

Methods

Two hundred Candida isolates (95 Candida albicans, 105 non-albicans Candida strains) were included in the study. Candida species were identified by conventional, biochemical and molecular methods. Antifungal susceptibility tests for amphotericin B, fluconazole, voriconazole, posaconazole, caspofungin and anidulafungin were performed with broth microdilution method according to the Clinical and Laboratory Standards Institute M27-A3 document.

Results

Of the 200 Candida strains, the most prevalent species were C. albicans (47.5 %), Candida glabrata (18.0 %) and Candida parapsilosis complex (14.0 %). All Candida species except for three (1.5 %) Candida kefyr strains were susceptible to amphotericin B. Only one (2.8 %) C. glabrata was resistant to fluconazole (MIC ≥ 64 μg/ml), and the others (97.2 %) exhibited dose-dependent susceptibility. All species, but C. glabrata strains, were susceptible to fluconazole. Resistance to voriconazole, posaconazole, caspofungin and anidulafungin was not detected in any strain.

Conclusion

Candida albicans were susceptible to all antifungal drugs. Three C. kefyr strains were resistant to amphotericin B. Only one C. glabrata was resistant to fluconazole. All the strains were susceptible to voriconazole, posaconazole, caspofungin and anidulafungin. In vitro antifungal susceptibility tests should be performed to select of appropriate and effective antifungal therapy, and monitor the development of resistance.

In Vitro Susceptibility and Trailing Growth Effect of Clinical Isolates of Candida Species to Azole Drugs

Background:

Emergence of resistance to respective antifungal drugs is a primary concern for the treatment of candidiasis. Hence, determining antifungal susceptibility of the isolated yeasts is of special importance for effective therapy. For this purpose, the clinical laboratory standard institute (CLSI) has introduced a broth microdilution method to determine minimum inhibitory concentration (MIC). However, the so-called “Trailing effect” phenomenon might sometimes pose ambiguity in the interpretation of the results.

Objectives:

The present study aimed to determine the in vitro susceptibility of clinical isolates of Candida against azoles and the frequency of the Trailing effect.

Materials and Methods:

A total of 193 Candida isolates were prospectively collected and identified through the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Using a broth microdilution test, according to the guidelines of CLSI M27-A3, antifungal susceptibilities of the isolated yeasts against Fluconazole (FLU), Itraconazole (ITR), Ketoconazole (KET) and Voriconazole (VOR) were assessed. Moreover, trailing growth was determined when a susceptible MIC was incubated for 24 hours, and turned into a resistant one after 48 hours of incubation.

Results:

Among the tested antifungal drugs in this study, the highest rate of resistance was observed against ITR (28.5%) followed by VOR (26.4%), FLU (20.8%) and KET (1.5%). The trailing effect was induced in 27 isolates (14.0%) by VOR, in 26 isolates (13.5%) by ITR, in 24 isolates (12.4%) by FLU, and in 19 isolates (9.8%) by KET.

Conclusions:

The monitoring of antifungal susceptibilities of Candida species isolated from clinical sources is highly recommended for the efficient management of patients. Moreover, the trailing effect should be taken into consideration once the interpretation of the results is intended.