Selection and antibacterial activity of bacteriocin-producing Bacilli from swine

Abstract:

[Background] Using traditional antibiotics as growth promoters in the pig industry leads to the richness and transmission of bacterial resistant genes. Thus, the identification and development of the emerging growth promoters as alternatives to antibiotics represents tremendous economic potential in feed additive industry. Probiotic cultures are interesting candidates as feed additives for food-producing animals. [Objective] This work had as main objectives to isolate Bacilli from the feces of free-range swine and then to characterize bacteriocins produced by Bacilli showing inhibition of typical gastrointestinal bacterial pathogens, in order to evaluate their potential as new growth promoters. [Methods] Using the dilution plate separation method and coated plate method, we screened culturable Bacilli. Strains presenting inhibitory properties for gastrointestinal bacterial pathogens were determined by Oxford cup method. The bacteriocin-producing Bacillus isolates were identified by 16S rRNA gene sequencing. [Results] Screening of 116 candidate strains isolated from feces samples resulted in the selection of six isolates presenting markedly inhibitory properties for bacterial pathogens, of which two strains were identified as Bacillus velezensis, three as Bacillus subtilis and one as Bacillus licheniformis. Among of them, B. licheniformis strain DY7 and B. subtilis strain FX4 exhibited the most effective inhibitory activity against the indicator pathogens, except for Salmonella enterica CICC10420, and were susceptible to Cefotaxime and Erythromycin. Additionally, both bacteriocins were stable over a wide range of pH 3.0?9.0 and temperatures 50?100 °C. [Conclusion] The effective inhibitory activity against the indicator pathogens and the stability may lead to the assumption that the strains DY7 and FX4 may be applied as pig growth promoters to control pathogens.