Bacteriocin production by Staphylococcus aureus involved in bovine mastitis in Brazil

In the present study, 257 Staphylococcus spp. strains were isolated from bovine mastitis cases in 56 different Brazilian dairy herds located in the southeast region of the country and tested for antimicrobial substance (AMS) production. Forty-six strains (17.9%) exhibited AMS production and their identification as Staphylococcus aureus was based on the presence of Gram-positive cocci and on positive results in tests for the ability to coagulate rabbit plasma, to ferment mannitol, and to produce acetoin. The AMS were characterized as bacteriocins (Bac) by their sensitivity to proteolytic enzymes. The Bac(+) strains were tested for resistance to 14 antimicrobial agents showing different profiles. Eighteen strains (39.0%) expressed a multiple antibiotic resistance phenotype. Forty-five strains exhibited at least one plasmid DNA. Cross-immunity analysis against strain S. aureus A70, which produces aureocin A70, amplification of the aurABCD operon (which encodes aureocin A70) or detection of this same operon by DNA/DNA hybridization revealed that 34 strains produce bacteriocins either identical or similar to aureocin A70. The remaining 12 Bac(+) strains produce antimicrobial peptides that seem to be distinct from the best characterized staphylococcal bacteriocins described thus far. The bacteriocin produced by strain 4185 may possess potential practical applications, since it was able to inhibit important pathogens such as Bacillus cereus, Listeria monocytogenes, and Staphylococcus spp. isolated from nosocomial infections.