DETECTION, IDENTIFICATION AND CHARACTERIZATION OF BACTERIOCIN-PRODUCING LACTIC-ACID BACTERIA FROM RETAIL FOOD-PRODUCTS

Forty bacteriocin-producing (Bac+) lactic acid bacteria (LAB) were iso lated from food samples purchased from retail supermarkets and local f arms. Of the 40 Bac+ isolates, 18 were isolated from 85 food samples b y enrichment (21% isolation rate) whereas eight were obtained from 63 samples by direct plating (13% isolation rate). By direct plating, Bac + LAB were detected at levels up to 2.4 x 10(5) cfu/g in ready-to-eat meats. The Bac+ isolates were identified by carbohydrate fermentation patterns, SDS-PAGE protein patterns, and other biochemical characteris tics; SDS-PAGE proved invaluable in identifying strains that could not be identified by other means. Differential inhibitory spectra against indicator microorganisms assisted in the identification of 19 unique Bac+ isolates. Bac+ LAB included Enterococcus faecalis, Lactobacillus curvatus, Lb. delbrueckii, Lb. plantarum, Lactococcus lactis, and Pedi ococcus acidilactici. Lb. curvatus (four strains) and Lc. lactis (nine strains) were the only isolates inhibitory to foodborne pathogens inc luding Listeria monocytogenes, Bacillus cereus, Clostridium perfringen s and Staphylococcus aureus. Some Lc. lactis isolates inhibited as man y as nine Gram-positive genera. Lb. curvatus FS47 and FS65 grew to hig h cell densities and produced bacteriocin at 6-degrees-C; however, Lc. lactis FS56 produced greater levels of bacteriocin at lower cell dens ities. The high incidence of Bac+ LAB detected in retail foods indicat es that the public is consuming a wide variety of Bac+ LAB that occur as natural contaminants. These data suggest a greater role for bacteri ocins as biopreservatives in food.