Resumo

Goat milk is intended for direct consumption and cheese processing. In this study, goat milk was used as source of bacteriocin-producing strains. Many lactic acid bacteria (LAB) produce bacteriocins with rather broad spectra of inhibition and could offer potential applications in food preservation. Bacteriocinogenic properties for strains isolated from goat milk were tested by agar spot-test against test panel of microorganisms, including Listeria monocytogenes from different serological groups and variety of LAB. Bacteriocin producing strains were identified using biochemical, physiological and biomolecular techniques. Some aspects of the mode of action against Listeria monocytogenes were also studied. A group of more than 100 LAB were isolated from goat milk collected from different regions of North-East of Brazil and pre-tested for the production of bacteriocin/s by agar spot-test against several food-borne pathogenic microorganisms. More than 20 isolates were selected for their effective inhibition on Listeria monocytogenes. The selected isolates were classified as member of Streptococcus, Lactobacillus and Enterococcus genus according to their biochemical, physiological characteristics and 16S rDNA sequencing. In MRS broth at 37^oC, bacteriocins secreted by selected strains were produced at various levels from 200 AU/ml to 3200 AU/mL. Their peptides were inactivated by proteolytic enzymes, but not when treated with α-amylase, catalase and lypase. The studied bacteriocins remained stable at pH from 2.0 to 10.0 and after exposure at 100^oC for 120 min and in presence of surfactants and salts. Tested strains presented a low profile when been examined for presence of virulence factors such as gelE, hyl, asa1, esp, cylA, efaA, ace, vanA, vanB, hdc1, hdc2, tdc, and odc. MIC for 17 different antibiotics have been determined. In conclusion, the bacteriocins produced by tested strains present activity against several LAB, L. monocytogenes from different serological groups and Gram-negative bacteria. Since the strains exhibited a strong antimicrobial activity against different L. monocytogenes strains and based on their survival in condition mimicking GIT and low level of presence of virulence factors and antibiotic resistance, they should be considered as a potential bio-preservatives starter cultures for fermented food productions with beneficial properties.