J. zyxwvutsrqponm Basic Microbiol. 37 (1997) 3, 187-196 (Bundesforschungsanstalt fur Ernahrung, Institut fiir Hygiene und Toxikologie, Engesserstr. 20, 76 13 1 Karlsruhe, Germany and ‘Department of Microbiology, University of the Witwatersrand, PO Wits 2050, Johannesburg, South Africa) Production of nisin-like bacteriocins by zyx Lactococcus lactis strains isolated from vegetables C. M. A. P. FRANZ, M. Du TOIT, A. von HOLY’, U. SCHILLINGER and W. H. HOLZAPFEL (Received zyxwvut I0 June 199MAccepted 23 January 1997) Four bacteriocin producing lactic acid bacteria isolated from vegetables were identified as Lactococcus lactis strains on the basis of physiological and biochemical characteristics, carbohydrate fermentation patterns and analysis of total soluble protein pattern by SDS PAGE. The bacteriocins had a wide spectrum of activity as antagonism was detected not only towards a variety of lactic acid bacteria, but also to Staphylococcus aureus and Listeria monocytogenes. These bacteriocins were resistant to heating at 12 1 z “C for 15 minutes and showed highest activity at low pH (<5.0). They were inactivated by the proteolytic enzymes a-chymotrypsin and proteinase K, but not by lipase, a-amylase, catalase or lysozyme. These bacteriocinogenic Lactococcus strains were all immune to the bacteriocins produced as well as to commerical nisin. Bacteriocin producer culture supernatants showed a high degree (70 or 100%) of cross-reactivity in the nisin ELISA, suggesting similarity of the produced bacteriocins to nisin. The potential application of bacteriocin producing lactococci of vegetable origin for safety assurance of vegetable foods and controlling vegetable fermentations is discussed. Bacteriocin production has been well documented for most representatives of the lactic acid bacteria (LAB) and has recently been reviewed by DE VUYST and VANDAMME (1994). Many bacteriocins produced by LAB are active not only against other LAB, but also against foodbornepathogens and toxinogens such as Listeria monocytogenes, Clostridiumpe$ringens, Bacillus cereus and Staphylococcus aureus (BHUNIA et al. 1988), OKEREKE and MONTVILLE 1991, UHLMAN et al. 1992, SCHILLINGER et al. 1995). This makes them attractive for use as natural food preservatives (STILES and HASTINGS 1991, DAESCHEL 1993, KIM 1993). Nisin has thus far been the only bacteriocin to find wide spread application in the food industry. It is produced by some Lactococcus lactis subsp. lactis strains and has bactericidal activity against a broad range of Gram-positive organisms including Listeria monocytogenes, Bacillus spp. and Clostridium spp. (DELVES-BROUGHTON 1990, HARRIS et al. 1992a). Nisin is permitted as a food additive in at least 46 countries, particularly for the inhibition of Clostridium spp. in cheese and canned foods (HURST 1981, DELVES-BROUGHTON 1990). Potential use of bacteriocins as biopreservatives has been studied in meat, dairy products or vegetable products (BERRY et al. 1991, FOEGEDING et al. 1992, HARRIS et al. 1992b, ROBERTS and ZOTTOLA 1993). Bacteriocin-producing LAB were used as starter cultures in vegetable fermentations to control the fermentation and achieve a product with consistent quality (HARRIS et al. 1992b, RUE-BARBA et al. 1994). Bacteriocinogenic LAB or their purified bacteriocins may, however, also be applied to improve the safety of non-fermented vegetable foods. Vegetables are often contaminated with high numbers of microorganismsand may harbour pathogenic microorganisms such as Listeria monocytogenes, Bacillus cereus and Staphylococcus aureus (UHLMAN et al. 1992, CARLIN and NGUYEN-THE 1994,BEUCHAT 1995). Commercial product surveys have reported that prepared salads are occasionally contaminated with low numbers of Listeria monocytogenes zy ( SIZMUR and WALKER 1988,UHLMAN et al. 1992,STEINBRUEGGE et al. 1988,GEORGE andLEv~n 1990).