Cell-Free Supernatant of Bacillus thuringiensis Displays Anti-Biofilm Activity Against Staphylococcus aureus.

Staphylococcus aureus is an important bacterial pathogen responsible for biofilm formation in medical devices. Due to the increasing antibiotic resistance of S. aureus, it is necessary to search for new anti-biofilm agents. In this study, the cell-free supernatant of Bacillus thuringiensis inhibited biofilm formation up to 93% and dispersed biofilms up to 83% without affecting the growth of S. aureus. The ethyl acetate extract of B. thuringiensis cell-free supernatant exhibited a dose-dependent anti-biofilm activity against S. aureus with the biofilm inhibition concentration ranging from 8 to 64 µg/mL. Scanning electron microscopy revealed that the cell-free supernatant extract of B. thuringiensis resulted in a significant reduction in S. aureus biofilms. The ethyl acetate extract of cell-free supernatant of B. thuringiensis was found to contain various compounds with structural similarity to known anti-biofilm compounds. In particular, squalene, cinnamic acid derivatives, and eicosapentaene seem to act synergistically against S. aureus biofilms. Hence, B. thuringiensis cell-free supernatant proved to be effective against S. aureus biofilms. The results clearly show the potential of natural molecules produced by B. thuringiensis as alternative therapies with anti-biofilm activity instead of bactericidal properties.

Production of co-polymers of polyhydroxyalkanoates by regulating the hydrolysis of biowastes.

Production of polyhydroxyalkanoate (PHA) co-polymers by Bacillus spp. was studied by feeding defined volatile fatty acids (VFAs) obtained through controlled hydrolysis of various wastes. Eleven mixed hydrolytic cultures (MHCs) each containing 6 strains could generate VFA from slurries of (2% total solids): pea-shells (PS), potato peels (PP), apple pomace (AP) and onion peels (OP). PS hydrolysates (obtained with MHC2 and MHC5) inoculated with Bacillus cereus EGU43 and Bacillus thuringiensis EGU45 produced co-polymers of PHA at the rate of 15-60mg/L with a 3HV content of 1%w/w. An enhancement in PHA yield of 3.66-fold, i.e. 205-550mg/L with 3HV content up to 7.5%(w/w) was observed upon addition of OP hydrolysate and 1% glucose (w/v) to PS hydrolysates. This is the first demonstration, where PHA co-polymer composition, under non-axenic conditions, could be controlled by customizing VFA profile of the hydrolysate by the addition of different biowastes.