ISOLATION OF BACTERIOCIN-PRODUCING STAPHYLOCOCCI FROM BRAZILIAN CHEESE

Abstract

ABSTRACT A total of 285 staphylococcus isolates were recovered from Minas Frescal cheese, a traditional Brazilian fresh cheese made with pasteurized milk, and screened for the production of bacteriocins. The staphylococci were isolated from 50 lots of commercial cheese, cultured on mannitol salt agar, checked for colony characteristics and catalase production, and classified as coagulase-positive (169) or coagulase-negative (116). Bacteriocin activity of cell-free culture supernatants was tested by the agar-well diffusion method against Listeria monocytogenes, Listeria ivanovii, Staphylococcus aureus and Streptococcus agalactiae as targets. Bacteriocin production was associated with 29 isolates (10%), including activity against L. monocytogenes (24), Staphylococcus aureus (26) and Streptococcus agalactiae (3). Analysis of DNA templates with primers for the staphylococcal bacteriocins aureocin A70 and A53, and staphylococcins C55α and β showed that all 24 isolates with antilisterial activity yielded polymerase chain reaction products and Southern blots that confirmed the presence of the aureocin A70 structural gene. However, only 20 of the 24 isolates carried the 8-kb plasmid that usually encodes aureocin production. Four additional isolates with activity only against Staphylococcus aureus tested negative for staphylococcin C55α and β may be producers of novel bacteriocins. The results confirmed that Staphylococcus aureus present in Minas Frescal cheeses may produce the antilisterial bacteriocin aureocin A70. PRACTICAL APPLICATIONS This research was carried out to detect staphylococci in samples of Brazilian Minas Frescal cheese made from pasteurized milk, and to analyze isolates for the capacity to produce bacteriocins with activity against potentially pathogenic bacteria involved in outbreaks of foodborne diseases. Although the presence of staphylococci in cheese samples implies unsanitary manufacturing conditions, the involvement of plasmids in bacteriocin production may offer opportunities to transfer critical components of such plasmids into food-grade bacteria that in turn may be useful in developing improved protocols for controlling the growth of Listeria and staphylococci in food systems.