New Candidate Substitution Of Antibiotics: Preliminary Study On Bacillus Thuringiensis Bacteriocins

Bacteriocins are natural peptides synthesized and secreted by bacteria, which inhibit the growth of both closely related and nonrelated species. Several bacteriocins have been proposed as potential alternatives to food pathogens. Current applications of bacteriocins serve as food preservatives caused by food pathogens by reason of its efficiencies, security and non-drug-resistance. Alternative strategies are desirable and bacteriocins represent attractive control agents to prevent food pathogens.The aim of this work was to evaluate the activities of 93 Bacillus thuringiensis (Bt) against 53 strains of food-borne pathogens. The results showed that the pathogens were susceptible to 75 of 93 Bt. Through bacteriocins produce bacterium select again,we found that the sequenced strains Bt HD1, 4AJ1 and 4BD1 had a wide antibacterial spectrum. They could inhibit gram-positie positive and gram-negative bacteria, including Bacillus cereus (Bc), Listeria monocytogenes (Lm), Enterococcus, Staphylococcus aureus (Sa) and Salmonella.The neutralized cell-free fermentation supernatant of Bt HD1, 4AJ1 and 4BD1 showed no antibacterial effects against Bc 0938, Bc ATCC 109873 and Lm ATCC 15313 in the first 8 h. Bt HD1 and 4AJ1 exhibited antibacterial effects against indicator strains at 10 h after incubation, while Bt 4BD1 showed inhibition effect against Bc 0938 till 24 h after incubation. The antibacterial activities of the fermentation supernatants were enhanced as time increase gradually and reached high levels between 24 h to 36 h. In the process, the inhibition activities presented fluctuations or even interruption.The bacteriocins produced by Bt HD1, 4AJ1 and 4BD1 were partially-purified with ammonium sulphate precipitation. After 50% to 100% ammonium sulphate precipitation, the partially-purified bacteriocins remained high antibacterial activities and tricine-SDS-PAGE indicated the protein nature of the partially-purified bacteriocins were abundant. Additionally, the molecular weights of the bactericions were estimated via SDS-PAGE and antibacterial activity detection of in situ on gels. Their molecular weights were about 6.5 kDa. The partially-purified bacteriocins remained strong antibacterial activities after exposure to 80 oC for 30 min, and within pH 3 to 9, suggesting its excellent thermostable property and pH resistance. The proteinase K had no influence while the activities were partially losted when the partially-purified bacteriocins were treated with chymotrypsin adn lipase.The partially-purified bacteriocins of Bt HD1, 4AJ1 and 4BD1 had differences in the antibacterial resistance patterns. The cells of Bc 0938, Bc ATCC 10987 and Lm ATCC 15313 were ultimate killed and lysised by the partially-purified bacteriocins of Bt HD1 and 4AJ1 while the cells of Bc 0938 was inhibited by the partially-purified bacteriocin of Bt HD1. The partially-purified bacteriocins of Bt HD1 and 4AJ1 could inhibit the spore germination of Bc 0938 and Bc ATCC 109873, but Bt 4BD1 could not. In hence, the partially-purified bacteriocins of Bt HD1 and 4AJ1 were bacteriocidal and bacteriolytic, while that of Bt 4BD1 exhibited an inhibition effect. Additionally, Bt HD1, 4AJ1 and 4BD1 were mainly resistant to amox/kclav, cefazolin, imipenem and oxacillin and susceptible to the other 18 antibiotics.