BackgroundSophorolipids are one of the most promising glycolipid biosurfactants and have been successfully employed in bioremediation and various other industrial sectors. They have also been described to exhibit antimicrobial activity against different bacterial species. Nevertheless, previous literature pertaining to the antifungal activity of sophorolipids are limited indicating the need for further research to explore novel strains with wide antimicrobial activity. A novel yeast strain, Rhodotorula babjevae YS3, was recently isolated from an agricultural field in Assam, Northeast India. This study was primarily emphasized at the characterization and subsequent evaluation of antifungal activity of the sophorolipid biosurfactant produced by R. babjevae YS3.ResultsThe growth kinetics and biosurfactant production by R. babjevae YS3 was evaluated by cultivation in Bushnell-Haas medium containing glucose (10% w/v) as the sole carbon source. A reduction in the surface tension of the culture medium from 70 to 32.6 mN/m was observed after 24 h. The yield of crude biosurfactant was recorded to be 19.0 g/l which might further increase after optimization of the growth parameters. The biosurfactant was characterized to be a heterogeneous sophorolipid (SL) with both lactonic and acidic forms after TLC, FTIR and LC–MS analyses. The SL exhibited excellent oil spreading and emulsifying activity against crude oil at 38.46 mm2 and 100% respectively. The CMC was observed to be 130 mg/l. The stability of the SL was evaluated over a wide range of pH (2–10), salinity (2–10% NaCl) and temperature (at 120 °C for time intervals of 30 up to 120 min). The SL was found to retain surface-active properties under the extreme conditions. Additionally, the SL exhibited promising antifungal activity against a considerably broad group of pathogenic fungi viz. Colletotrichum gloeosporioides, Fusarium verticilliodes, Fusarium oxysporum f. sp. pisi, Corynespora cassiicola, and Trichophyton rubrum.ConclusionsThe study reports, for the first time, the biosurfactant producing ability of R. babjevae, a relatively lesser studied yeast. The persistent surface active properties of the sophorolipid in extreme conditions advocates its applicability in diverse environmental and industrial sectors. Further, antifungal activities against plant and human pathogens opens up possibilities for development of efficient and eco-friendly antifungal agents with agricultural and biomedical applications.

BackgroundThe increasing and rapid spread of metallo-beta-lactamase (MBL) producing Enterobacteriaceae, particularly Escherichia coli and Klebsiella pneumoniae represents an emerging public health threat. However, limited data is available on MBL production in clinical isolates of E. coli and K. pneumoniae from Nepal. We have therefore undertaken this study to ascertain the incidence of MBL production in clinical isolates of E. coli and K. pneumoniae at a tertiary care teaching hospital in central Nepal.MethodsA total of 401 consecutive, non-duplicate isolates of E. coli (n = 216) and K. pneumoniae (n = 185) were recovered from various clinical samples between July and December, 2012. These isolates were screened for the detection of carbapenemase production on the basis of their reduced susceptibility to meropenem or ertapenem by the disc diffusion method. The screened isolates were further phenotypically studied for carbapenemase production by modified Hodge test (MHT). MBL production was detected by performing combined disc test by using imipenem discs with and without ethylenediaminetetraacetic acid (EDTA), which chelates zinc required for MBL activity.ResultsOut of 216 E. coli isolates, a total of 41 isolates (18.98%) and out of 185 K. pneumoniae isolates, a total of 39 isolates (21.08%) were suspected to be carbapenemase- producers on the basis of their reduced susceptibility to meropenem or ertapenem. Interestingly, all the initially suspected isolates of E. coli and K. pneumoniae for carbapenemase production were found to be positive in both MHT and combined disc test. However, few weakly positive reactions were observed in MHT. All the MBL producing isolates were multidrug-resistant (MDR). In addition, 75.60% E. coli and 71.79% of K. pneumoniae isolates producing MBL were found to be “pandrug- resistant”.ConclusionsOur findings showed MBL production in a considerable number of E. coli and K. pneumoniae isolates with MDR and pandrug-resistant phenotypes. Combined disc method can provide a sensible choice for phenotypic detection of MBL production in clinical microbiology laboratories as detection of MBL in bacterial isolates is indispensable for establishing the effective antibiotic policies and infection control strategies in the hospital setting.

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Our findings highlight the incidence of blaNDM-1 in E. coli isolates with a reduced susceptibility to meropenem or ertapenem.

This study constituted a primer report on high prevalence of blaTEM and blaCTX-M genes in ESBL producing isolates of E. coli and K. pneumoniae and denotes the need of more extensive studies on these antibiotic genes to determine the magnitude of the problem of antibiotic resistance exiting in this locality.

Dermatophytic infections caused by Trichophyton rubrum are the most prevalent superficial mycoses worldwide. The present study was aimed at evaluating the anti‐dermatophytic effect of a rhamnolipid biosurfactant (RL) produced by Pseudomonas aeruginosa SS14 (GenBank Accession no. KC866140) against T. rubrum in experimentally induced dermatophytosis in mice models. The purified RL could effectively suppress spore germination and hyphal proliferation of T. rubrum at 500 μg/mL. Ultramicroscopic observations involving SEM and AFM studies revealed severely altered hyphal morphology in the RL‐treated mycelia. The membrane disruptive effect of RL was measured by the uptake of propidium iodide (PI) as visualized by CLSM. The absorbance of the RL‐treated cell suspension at 260 nm showed concentration‐dependant exudation of nucleic acid due to loss of cell membrane integrity. On evaluation of the therapeutic efficacy of RL on experimentally induced cutaneous dermatophytosis in mice models, we observed that the RL, when applied topically at a concentration of 500 μg/mL, was effective in completely curing dermatophytosis at the end of 21‐day treatment period. The results were statistically similar to those obtained using the standard drug terbinafine as control. Apart from macroscopic observation, the results were confirmed by culture of skin scrapings and histopathological examination. The results are suggestive of the effectiveness of RL in control of dermatophytosis caused by T. rubrum.

Highlights First report of the activity of rhamnolipid (RL) against dermatophytic biofilms. RL acts as an anti-biofilm agent against T. rubrum and T. mentagrophytes . RL inhibits biofilm formation as well as disrupts mature biofilms. Marked reduction of biomass and extracellular matrix of biofilms on RL exposure. RL was characterized using FT-IR, HPLC-ESI-MS, and GC–MS.

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