Submitted to: Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2011
Publication Date: 8/1/2011
Citation: Brito, M.A., Somkuti, G.A., Renye Jr, J.A. 2011. Isolation of bacteriocin-producing staphylococci from Brazilian cheese. Journal of Food Safety. 31:365-370.
Interpretive Summary: The bacteriological survey of 50 lots of the popular Brazilian style Minas Frescal cheese resulted in the isolation of staphylococci which are frequently involved in outbreaks of food borne disease. Since the cheeses were prepared from pasteurized milk, the presence of staphylococci indicated possible contamination due to inadequate sanitary practices in the manufacturing facilities. Using various screening tests, approximately 10 percent of staphylococcal strains were identified as carriers of genes needed for the production of natural antimicrobial products that inhibit bacteria involved in milk-borne diseases such as Listeria and other staphylococci. These beneficial activities may be transferable to food fermentation microbes used in the preparation of cheeses, yogurts and other fermented dairy foods and may be used in developing newer approaches to protecting foods from bacteria causing food borne illnesses, particularly by suppressing the growth of toxin producing staphylococci and Listeria.
Technical 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 antibacterial substances. The staphylococci were isolated from 50 lots of commercial cheese and cultured on mannitol salt agar. Isolates were checked for colony characteristics and cell morphology, catalase production and further classified as coagulase-positive (169) or coagulase-negative (116) by the tube coagulase test. Bacteriocin activity of cell-free supernatants of overnight cultures was tested by the agar-well diffusion method with Listeria monocytogenes, L. ivanovii, Staphylococcus aureus and Streptococcus agalactiae as targets. Bacteriocin production was associated with 29 isolates (10%), including activity against L. monocytogenes (24), S. aureus (26), and S. agalactiae (3). Plasmid samples isolated from bacteriocin-producing isolates were checked with PCR techniques using primers specific to the staphylococcal bacteriocins aureocin A70 and A53, and staphylococcins C55a and ß. All 24 isolates with antilisterial activity yielded PCR products and positive Southern blots indicating the presence of the aureocin A70 structural gene but only 20 of the 24 isolates carried the 8-kb plasmid that is usually associated with aureocin production. The four additional isolates active against S. aureus only and tested negative with staphylococcin C55a and ß primers, may be producers of novel bacteriocins. The results have shown that antilisterial cheese isolates of S. aureus produced plasmid borne aureocin A70 similar to strains often recovered from bovine milk. Bacteriocin production may increase the competitiveness of the producing strain and may also have a role in preventing contamination by L. monocytogenes.