Objectives Candida auris is an emerging, often MDR, yeast pathogen. Efficient animal models are needed to study its pathogenicity and treatment. Therefore, we developed a C. auris fruit fly infection model. Methods TollI-RXA/Tollr632 female flies were infected with 10 different C. auris strains from the CDC Antimicrobial Resistance bank panel. We used three clinical Candida albicans strains as controls. For drug protection assays, fly survival was assessed along with measurement of fungal burden (cfu/g tissue) and histopathology in C. auris-infected flies fed with fluconazole- or posaconazole-containing food. Results Despite slower in vitro growth, all 10 C. auris isolates caused significantly greater mortality than C. albicans in infected flies, with >80% of C. auris-infected flies dying by day 7 post-infection (versus 67% with C. albicans, P < 0.001–0.005). Comparison of C. auris isolates from different geographical clades revealed more rapid in vitro growth of South American isolates and greater virulence in infected flies, whereas the aggregative capacity of C. auris strains had minimal impact on their growth and pathogenicity. Survival protection and decreased fungal burden of fluconazole- or posaconazole-fed flies infected with two C. auris strains were in line with the isolates’ disparate in vitro azole susceptibility. High reproducibility of survival curves for both non-treated and antifungal-treated infected flies was seen, with coefficients of variation of 0.00–0.31 for 7 day mortality. Conclusions Toll-deficient flies could provide a fast, reliable and inexpensive model to study pathogenesis and drug activity in C. auris candidiasis.

Accurate characterization of melanin using analytical methodologies has proved to be difficult due to its heterogeneity, insolubility in wide pH and broad range of solvents. The present study was undertaken to characterize melanin extracted from an environmental Aspergillus fumigatus AFGRD105 by studying its genes, chemical properties and spectral data. A gene based approach to confirm the type of melanin carried out indicated the extracted melanin to be of the dihydroxynaphthalene type. On comparison with synthetic melanin, UV–Vis and IR spectra of the extracted melanin revealed characteristic peaks that can be further used for confirmation of DHN-melanin extracted from any source. Solid state 13C NMR spectroscopy established the presence of the hydroxyl-naphthalene moiety and validated the results obtained by genetic analysis. The correct assignment of the observed spectral frequency characteristic of functional groups can be further adapted in future works that deal with binding capacities and biomolecule systems involving melanin.

Melanins are indolic polymers produced by many genera included among plants, animals and microorganisms and targeted mainly for their wide range of applications in cosmetics, agriculture and medicine. An approach to analyse the cumulative effect of parameters for enhanced melanin production was carried out using response surface methodology. In this present study, optimization of media and process parameters for melanin production from Aspergillus fumigatus AFGRD105 (GenBank: JX041523; NFCCI accession number: 3826) was carried out by an initial univariate approach followed by statistical response surface methodology. The univariate approach was used to standardise the parameters that can be used for the 12-run Plackett–Burman design that is used for screening for critical parameters. Further optimization of parameters was analysed using Box–Behnken design. The optimum conditions observed were temperature, moisture and sodium dihydrogen phosphate concentration. The yield of every run of both designs were confirmed to be melanin by laboratory tests of analysis in the presence of acids, base and water. This is the first report confirming an increase in melanin production A. fumigatus AFGRD105 without the addition of costly additives.

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Bioremediation of chromates using bacteria primarily involves the removal/reduction of heavy metals in effluent using indigenous micro-organisms such as chromium reducing bacteria as biosorbents for cleaner and healthier environment. In the present study, the removal of hexavalent chromium by micro-organisms isolated from acclimatized tannery effluent was investigated. Biochemical assays and molecular sequencing revealed strain SRS05 to be Stenotrophomonas maltophilia. Resistance to chromium was determined by agar and broth dilution assays followed by determination of minimal inhibitory concentration. Strain SRS05 was able to resist 400 mg/ml of chromium which reflects that the heavy metal could be utilized by the micro-organism for its growth. Results by atomic absorption spectroscopy, Fourier transform infrared spectroscopic analysis and scanning electron microscopy revealed effective biosorption of chromium by S. maltophilia SRS05 with no intracellular changes morphologically indicating the stability of the organism in the presence of chromium. It is therefore recommended that this bacterium can be used widely for remediation of hexavalent chromium although the genetic basis for observations concluded in this study is to be confirmed.