Candida albicans is considered as the primary etiologic agent of candidiasis, a very common fungal infection in human. The yeast to hyphal transition and ability to form hypoxic biofilm on medical devices is well allied with virulence and antifungal resistance of C. albicans. Antagonistic agents that inhibit biofilm formation and alter susceptibility of C. albicans to conventional antifungals is of profound need. The present study explores the antibiofilm efficacy of Bacillus subtilis, a marine bacterial isolate from Palk Bay against C. albicans. Mass spectrometric analysis of ethyl acetate extract of B. subtilis unveiled 5-hydroxymethyl-2-furaldehyde (5HM2F) as one of its major components. 5HM2F demonstrated concentration dependent biofilm inhibition, which was also corroborated through microscopic analysis. Furthermore, 5HM2F was effective in inhibiting other virulence factors of C. albicans such as morphological transition and secreted hydrolases production. Fourier transform infrared spectroscopic analysis showed alteration in amide bond region. The reduction in ergosterol content and increased antifungal susceptibility was well allied with real time PCR result, which showed down regulation of genes involved in drug resistance mechanisms. In vivo study using Caenorhabditis elegans also substantiated the antivirulence efficacy of 5HM2F at in vivo condition. Thus, the present study reports the therapeutic potential of 5HM2F against C. albicans infections.

BackgroundGroup A streptococcus (GAS, Streptococcus pyogenes), a multi-virulent, exclusive human pathogen responsible for various invasive and non-invasive diseases possesses biofilm forming phenomenon as one of its pathogenic armaments. Recently, antibiofilm agents have gained prime importance, since inhibiting the biofilm formation is expected to reduce development of antibiotic resistance and increase their susceptibility to the host immune cells.Principal FindingsThe current study demonstrates the antibiofilm activity of 3Furancarboxaldehyde (3FCA), a floral honey derived compound, against GAS biofilm, which was divulged using crystal violet assay, light microscopy, and confocal laser scanning microscopy. The report is extended to study its effect on various aspects of GAS (morphology, virulence, aggregation) at its minimal biofilm inhibitory concentration (132μg/ml). 3FCA was found to alter the growth pattern of GAS in solid and liquid medium and increased the rate of auto-aggregation. Electron microscopy unveiled the increase in extra polymeric substances around cell. Gene expression studies showed down-regulation of covR gene, which is speculated to be the prime target for the antibiofilm activity. Increased hyaluronic acid production and down regulation of srtB gene is attributed to the enhanced rate of auto-aggregation. The virulence genes (srv, mga, luxS and hasA) were also found to be over expressed, which was manifested with the increased susceptibility of the model organism Caenorhabditis elegans to 3FCA treated GAS. The toxicity of 3FCA was ruled out with no adverse effect on C. elegans.SignificanceThough 3FCA possess antibiofilm activity against GAS, it was also found to increase the virulence of GAS. This study demonstrates that, covR mediated antibiofilm activity may increase the virulence of GAS. This also emphasizes the importance to analyse the acclimatization response and virulence of the pathogen in the presence of antibiofilm compounds prior to their clinical trials.

Biofilm formation is a major contributing factor in the pathogenesis of Vibrio cholerae O1 (VCO1) and therefore preventing biofilm formation could be an effective alternative strategy for controlling cholera. The present study was designed to explore seawater bacteria as a source of anti-biofilm agents against VCO1. Indole-3-carboxaldehyde (I3C) was identified as an active principle component in Marinomonas sp., which efficiently inhibited biofilm formation by VCO1 without any selection pressure. Furthermore, I3C applications also resulted in considerable collapsing of preformed pellicles. Real-time PCR studies revealed the down-regulation of virulence gene expression by modulation of the quorum-sensing pathway and enhancement of protease production, which was further confirmed by phenotypic assays. Furthermore, I3C increased the survival rate of Caenorhabditis elegans when infected with VCO1 by significantly reducing in vivo biofilm formation, which was corroborated by a survivability assay. Thus, this study revealed, for the first time, the potential of I3C as an anti-biofilm agent against VCO1.

Fukugiside exhibits potent anti-biofilm and anti-virulence activity against different M serotypes of S. pyogenes. It is also non-toxic, which augurs well for its clinical application.