Antibacterial activity of polysaccharide Bacillus subtilis and Leuconostoc mesenteroides under submerged fermentation

Abstract

This study aimed to synthesize exopolysaccharides from bacterial isolates from the Egyptian ecology and apply them to combat foodborne bacteria. In the investigation, 66 bacterial isolates were isolated from various sources (soil, cane juice, and spoilage cucumber). Among the 66 bacterial isolates tested, 40 exhibited the capacity to produce exopolysaccharides (29 isolates produced levan, and 11 isolates produced dextran), giving the slimy colonies and mucoid viscosity appearance in the broth medium. The 40 polymer bacterial isolates evaluated for antibacterial efficacy against foodborne pathogenic bacteria strains (Escherichia coli O157H7, Salmonella typhimirium As3, Staphylococcus aureus As4, Bacillus cereus DSMZ345, Pseudomonas aeruginosa ATOC27853 and Listeria monocytogenes As1). Six polymers-producing isolates out of 40 demonstrated the highest significant antibacterial activity, with minimum inhibitory concentration values ranging from 1000 to 12.5 mg/mL. The chosen polymers exhibited bacteriostatic properties. The most efficient isolates were phenotypically identified as Leuconostoc mesenteroides for the dextran-producing isolates with codes J1, J2, SCs1, SCs3, and SCg2, and Bacillus subtilis for the levan-producing isolate with code B. Among the six isolates, L. mesenteroides isolate code SCg2 produced the most dextran polymer with a dry weight of 6.36 g/L, productivity of 0.088 g/L/h, and a polymer yield coefficient relative to biomass of 1.55 g/g/L. Further nuclear magnetic resonance research demonstrated that the dextran polymer was composed of glucose with α-(1→6) links, with a 1H NMR spectrum ranging from δ 3.44 to 3.92 ppm. Dextran polymer produced from L. mesenteroides isolate code SCg2 was therefore selected for consumption during food preservation as a film coating to increase the product's shelf life.