Potentiation of antibiotic against Pseudomonas aeruginosa biofilm: a study with plumbagin and gentamicin.

AIMS: Pseudomonas aeruginosa is one of the fatal biofilm-forming pathogens which pose to be a problem in clinical infections, contamination of food and marine ecosystems. In this report, a naphthoquinone-plumbagin has been explored for its antimicrobial (antibacterial and antibiofilm) activity against P. aeruginosa biofilm. The ability of plumbagin to enhance the bioactivity of a known broad-spectrum antibiotic was further assayed by combining the sub-MIC doses of plumbagin with sub-MIC doses of gentamicin against P. aeruginosa biofilm. METHODS AND RESULTS: This combinatorial approach was used for a series of experiments for understanding the mechanism of action for antibiofilm activity against P. aeruginosa (MTCC 424, MTCC 2488). Antibiofilm activity was studied by safranin staining, estimating total protein, visualization of biofilms and extra polymeric substances quantification. Antivirulent activity of these doses was studied by azocasein degradation, expression of virulent factors and molecular docking. Expression of quorum sensing (QS) phenotypes was studied by motility assessment and mRNA expression pattern of virulence genes. It was observed that plumbagin alone and the combinatorial doses of plumbagin and gentamicin exhibit significant antibiofilm and antivirulent activity coupled with the reduction in the expression of QS phenotypes and virulence genes. Molecular docking study revealed that plumbagin had variable affinity for different QS proteins. CONCLUSION: Low doses of plumbagin and gentamicin exhibit synergistic activity against P. aeruginosa biofilm while maintaining their effectiveness. SIGNIFICANCE AND IMPACT OF THE STUDY: As the P. aeruginosa biofilms are reservoir of persister bacteria, thus, the increasing concern of antibiotic tolerance has to be dealt with combinatorial approaches. In this report, plumbagin has been explored in potentiating the antibiofilm effect of a broad-spectrum antibiotic gentamicin for better therapeutic efficacy.

Bioconversion of fish solid waste into PHB using Bacillus subtilis based submerged fermentation process.

Currently, one of the major problem affecting the world is solid waste management, predominantly petroleum-based plastic and fish solid waste (FSW). However, it is very difficult to reduce the consumption of plastic as well as fish products, but it is promising to convert FSW to biopolymer to reduce eco-pollution. On account of that, the bioconversion of FSW extract to polyhydroxybutyrate (PHB) was undertaken by using Bacillus subtilis (KP172548). Under optimized conditions, 1.62 g/L of PHB has been produced by the bacterium. The purified compound was further characterized by advanced analytical technologies to elucidate its chemical structure. Results indicated that the biopolymer was found to be PHB, the most common homopolymer of polyhydroxyalkanoates (PHAs). This is the first report demonstrating the efficacy of B. subtilis to utilize FSW extract to produce biopolymer. The biocompatibility of the PHB against murine macrophage cell line RAW264.7 demonstrated that, it was comparatively less toxic, favourable for surface attachment and proliferation in comparison with poly-lactic acid (PLA) and commercially available PHB. Thus, further exploration is highly indispensable to use FSW extract as a substrate for production of PHB at pilot scale.