Seleção de bactérias láticas do leite de transição bovino fermentado e efeito antagônico frente a Escherichia coli e Staphylococcus aureu

Abstract

Lactic acid bacteria (BALs) produce substances that can aid in the control of bacterial diseases and inhibit the growth of pathogenic and deteriorating microorganisms in food. The antibacterialactivity of these bacteria is of great interest in animal and human health in the pharmaceutical and food industries, as they may reduce the use of conventional antimicrobials. The genus Lactobacillus is one of the most studied for producing bacteriocins that inhibit the growth ofpathogenic microorganisms like Staphylococcus aureus and Escherichia coli. The objective of this study was to evaluate the in vitro inhibitory potential of lactic acid bacteria from bovine fermented transition milk against strains of Escherichia coli and Sthaphylococcus aureus ofbovine origin. For article I, lactic acid bacteria were isolated from fermented bovine transition milk anaerobically for 141 days. The samples were submitted to physical-chemical analysis of pH and titratable acidity and microbiological analyzes for quantification of lactic bacteria,enterobacteria, fungi and yeasts. Bacteria isolated were presumptively identified in the API gallery, evaluated for fermentation capacity, their probiotic potential in vitro by tolerance to gastric pH and bile salts, and antagonism to Escherichia coli. The samples had high lactic acidcounts and low S. aureus counts. Three strains were identified as Lactobacillus brevis and resisted at acid pH and bile salts. However, only Lactobacillus brevis (A1) presented an antagonistic effect. For article II, lactic acid bacteria were isolated from fermented bovine transition milk anaerobically for 33 days. Bacteria isolated were identified by proteomic analysis and evaluated for antimicrobial susceptibility, S. aureus antagonism and biofilm inhibition efficiency adhered to stainless steel surface and teat rubber. Among the BAL isolates evaluated, Lactobacillus paracasei, Lactobacillus casei, Lactobacillus rhamnosus, andEnterococcus spp. Were identified. These bacteria were sensitive to five antimicrobials used in the treatment of bovine mastitis. From the total of 15 isolates of BAL, nine showed zones of inhibition against two samples of S. aureus in diffusion test in agar by overlay. . The reductionefficiencies of these biofilms ranged from 12 to 15% on the steel and rubber surfaces respectively. The results indicate that BAL from fermented transition milk have inhibitory effects against E. coli and S. aureus and may represent an alternative source for the control of diarrheain calves, biofilm reduction and prevention of mastitis control in cattle.