INACTIVATION AND ATTACHMENT OF LISTERIA-MONOCYTOGENES ON BEEF MUSCLE TREATED WITH LACTIC-ACID AND SELECTED BACTERIOCINS

Cubical pieces (1 cm3) of aseptically obtained beef muscle were treated with lactic acid (2%), nisin (4 x 10(4) IU/ml) and pediocin PO2 (a bacteriocin produced by Pediococcus acidilactici PO2; 3.2 x 10(3) arbitrary units/ml). Treated meat was immersed for 1 min in a cell suspension of a mixture of two strains of Listeria monocytogenes and then stored for 48 h at 4-degrees-C. Meat cubes were analyzed immediately after immersion in the cell suspension, then after 1, 24, and 48 h of storage. Count of L. monocytogenes per cube and percentage of attached cells were determined. Data indicated that the antimicrobial agents significantly (p = 0.05) decreased the count of L. monocytogenes during the 48-h storage by 1.7, 1.1, and 0.6 log10 CFU/6 cm2 of meat surface for lactic acid, nisin, and pediocin PO2 treatments, respectively. Lactic acid on the meat surface had an immediate and also a delayed listericidal action, but bacteriocins only inhibited L. monocytogenes immediately, and had little or no delayed antilisterial effect. The percentage of Listeria cell attached to the beef muscle significantly (p = 0.05) increased in the presence of lactic acid, but th value did not change significantly- or slightly decreased in th presence of nisin and pediocin PO2, respectively.