Stability of Mueller-Hinton agar supplemented with glucose and methylene blue for disk diffusion testing of fluconazole and voriconazole

Isolation, speciation and antifungal susceptibility testing of Candida isolates from various clinical specimens at a tertiary care hospital, Nepal

BACKGROUND

Candida species are responsible for various clinical infections ranging from mucocutaneous infection to life threatening invasive diseases along with increased resistance to antifungal drugs has made a serious concern. Resistance to antifungal agents has increased during the last decade. Thus, identification of Candida up to species level and its antifungal susceptibility testing has a paramount significance in the management of Candidal infections. The aim of the study was to speciate Candida species and to determine antifungal susceptibility pattern of Candida species to antifungal agents.

METHODS

A total of 100 consecutive Candida species were isolated from 1248 clinical specimens over 7 months period. Growths on Sabouraud dextrose agar were evaluated for colony appearance, macroscopic examination, Gram staining, germ tube test and urea hydrolysis test. Further, they were processed for Candida speciation on CHROMagar. Antifungal susceptibility testing was performed as recommended by Clinical and Laboratory Standards Institute (CLSI) M44-A document.

RESULTS

Out of 100 Candida isolates, Candida albicans (56%) was the most common species. Among the non-albicans Candida species, Candida tropicalis (20%) was the predominant isolate followed by Candida glabrata (14%). Regarding antifungal susceptibility pattern, Candida species were more susceptible to clotrimazole (82%) followed by fluconazole (64%) and miconazole (44%).

CONCLUSIONS

Candida albicans was the predominant species responsible for various Candidal infections. Among commonly used antifungal drugs clotrimazole, miconazole and fluconazole were most effective.

Endophytic Actinobacteria from the Brazilian Medicinal Plant Lychnophora ericoides Mart. and the Biological Potential of Their Secondary Metabolites

Endophytic actinobacteria from the Brazilian medicinal plant Lychnophora ericoides were isolated for the first time, and the biological potential of their secondary metabolites was evaluated. A phylogenic analysis of isolated actinobacteria was accomplished with 16S rRNA gene sequencing, and the predominance of the genus Streptomyces was observed. All strains were cultured on solid rice medium, and ethanol extracts were evaluated with antimicrobial and cytotoxic assays against cancer cell lines. As a result, 92% of the extracts showed a high or moderate activity against at least one pathogenic microbial strain or cancer cell line. Based on the biological and chemical analyses of crude extracts, three endophytic strains were selected for further investigation of their chemical profiles. Sixteen compounds were isolated, and 3-hydroxy-4-methoxybenzamide (9) and 2,3-dihydro-2,2-dimethyl-4(1H)-quinazolinone (15) are reported as natural products for the first time in this study. The biological activity of the pure compounds was also assessed. Compound 15 displayed potent cytotoxic activity against all four tested cancer cell lines. Nocardamine (2) was only moderately active against two cancer cell lines but showed strong activity against Trypanosoma cruzi. Our results show that endophytic actinobacteria from L. ericoides are a promising source of bioactive compounds.

Biological activities of Pseudevernia furfuracea (L.) Zopf extracts and isolation of the active compounds

ETHNOPHARMACOLOGICAL RELEVANCE

Pseudevernia furfuracea (L.) Zopf (Parmeliaceae) is a common epiphytic lichen in the conifer-hardwood forest of Anatolia. This species is used in traditional medicine in Turkey as a treatment for wounds, eczema and hemorrhoids.

AIM OF THE STUDY

The present study was designed to investigate the active compounds from Pseudevernia. furfuracea, and the isolation studies yielded atraric acid (Aslan et al., 2006) as the major compound and a mixture of methyl hematommate (Baumann, 1960) and methyl chlorohematommate (Bayır et al., 2006). Furthermore, methanolic extract from thalli of Pseudevernia. furfuracea and its fractions and isolates (Aslan et al., 2006; Baumann, 1960; Bayır et al., 2006) were investigated for in vitro antimicrobial and antioxidant activities, and in vivo antinociceptive, anti-inflammatory and wound healing activities.

MATERIAL AND METHODS

Antimicrobial activities of the samples were determined by using the disc diffusion technique. 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was used as a rapid TLC screening method to evaluate the antioxidant activity of Pseudevernia. furfuracea. The thiobarbituric acid (TBA) test was used to assess the efficacy of the extracts in protecting liposomes from lipid peroxidation. In vivo inhibitory effect of the extracts on the carrageenan-induced hind paw edema model in mice was studied for the assessment of anti-inflammatory activity. p-Benzoquinone-induced abdominal constriction test was used to explore the antinociceptive effects of the extracts. Moreover, the wound healing potential of the plant extracts that were evaluated by using in vivo incision and excision wound models on rats and mice, were comparatively assessed with a reference ointment Madecassol(®).

RESULTS

Significant antimicrobial activities were observed against Gram (+) microorganisms and Candida krusei and Candida. dubliniensis in dichloromethane (DCM) and ethyl acetate (EtOAc) extracts and isolates. The methanol (MeOH), DCM and EtOAc extracts of the lichen were found to possess moderate inhibitory activity on lipid peroxidation. Methanolic extract of the lichen was found to possess significant inhibitory activity on the carrageenan-induced hind paw edema model in mice whereas the other fractions did not show any activity. While DCM and EtOAc extracts and fractions showed notable anti-inflammatory activity on carrageenan-induced hind paw edema model without inducing any apparent acute toxicity or gastric damage. Moreover, topical application of the ointment prepared with MeOH extract and EtOAc fraction onto the incised wounds exerted remarkable wound healing activity.

CONCLUSION

The results of these experimental studies exhibited that nonpolar fractions of Pseudevernia. furfuracea have significant antimicrobial activity against especially Candida species and polar fractions (especially MeOH) display antioxidant, anti-inflammatory, antinociceptive and wound healing activities.

Correlation between Etest, disk diffusion, and microdilution methods for antifungal susceptibility testing of Candida species from infection and colonization

The correlation between the microdilution (MD), Etest (ET), and disk diffusion (DD) methods was determined for amphotericin B, itraconazole and fluconazole. The minimal inhibitory concentration (MIC) of those antifungal agents was established for a total of 70 Candida spp. isolates from colonization and infection. The species distribution was: Candida albicans (n=27), C. tropicalis (n=17), C. glabrata (n=16), C. parapsilosis (n=8), and C. lusitaniae (n=2). Non-Candida albicans Candida species showed higher MICs for the three antifungal agents when compared with C. albicans isolates. The overall concordance (based on the MIC value obtained within two dilutions) between the ET and the MD method was 83% for amphotericin B, 63% for itraconazole, and 64% for fluconazole. Considering the breakpoint, the agreement between the DD and MD methods was 71% for itraconazole and 67% for fluconazole. The DD zone diameters are highly reproducible and correlate well with the MD method, making agar-based methods a viable alternative to MD for susceptibility testing. However, data on agar-based tests for itraconazole and amphotericin B are yet scarce. Thus, further research must still be carried out to ensure the standardization to other antifungal agents.

Current status of antifungal susceptibility testing methods

Antifungal susceptibility testing is a very dynamic field of medical mycology. Standardization of in vitro susceptibility tests by the Clinical and Laboratory Standards Institute (CLSI) and the European Committee for Antimicrobial Susceptibility Testing (EUCAST), and current availability of reference methods constituted the major remarkable steps in the field. Based on the established minimum inhibitory concentration (MIC) breakpoints, it is now possible to determine the susceptibilities of Candida strains to fluconazole, itraconazole, voriconazole, and flucytosine. Moreover, utility of fluconazole antifungal susceptibility tests as an adjunct in optimizing treatment of candidiasis has now been validated. While the MIC breakpoints and clinical significance of susceptibility testing for the remaining fungi and antifungal drugs remain yet unclear, modifications of the available methods as well as other methodologies are being intensively studied to overcome the present drawbacks and limitations. Among the other methods under investigation are Etest, colorimetric microdilution, agar dilution, determination of fungicidal activity, flow cytometry, and ergosterol quantitation. Etest offers the advantage of practical application and favorable agreement rates with the reference methods that are frequently above acceptable limits. However, MIC breakpoints for Etest remain to be evaluated and established. Development of commercially available, standardized colorimetric panels that are based on CLSI method parameters has added more to the antifungal susceptibility testing armamentarium. Flow cytometry, on the other hand, appears to offer rapid susceptibility testing but requires specified equipment and further evaluation for reproducibility and standardization. Ergosterol quantitation is another novel approach, which appears potentially beneficial particularly in discrimination of azole-resistant isolates from heavy trailers. The method is yet investigational and requires to be further studied. Developments in methodology and applications of antifungal susceptibility testing will hopefully provide enhanced utility in clinical guidance of antifungal therapy. However, and particularly in immunosuppressed host, in vitro susceptibility is and will remain only one of several factors that influence clinical outcome.

Development of anidulafungin for disk diffusion susceptibility testing against Candida spp

A disk diffusion (DD) method has been standardized by the Clinical and Laboratory Standards Institute (M44-A) to test Candida susceptibilities for some azoles (fluconazole and voriconazole). The DD method using anidulafungin, a new echinocandin, was initially developed here using Candida spp. (75 strains) and candidate anidulafungin disk concentrations of 1, 2, 5, and 10 microg with or without dimethyl sulfoxide (DMSO) (0.05-1%) and with or without polysorbate 80 (P-80, 0.002-2%). The 2-microg disks (with 1% DMSO and 0.1% P-80) produced acceptable correlation statistics (r = 0.84-0.85 ) when compared with reference MIC results, and this disk was optimal for testing all Candida spp. Good separation of Candida parapsilosis (least anidulafungin-susceptible species) from the more susceptible yeast species and a potential susceptibility breakpoint near the preferred reproducible zone diameter of > or = 15 mm were achieved for all tested yeast species.