Isolation of nisin-producing Lactococcus lactis WNC 20 strain from nham, a traditional Thai fermented sausage.

A total of 14,020 lactic acid bacteria (LAB) were isolated from nham and screened for bacteriocin production. One Lactococcus lactis strain WNC 20 produced a bacteriocin that not only inhibited closely related LAB, but also some food-borne pathogens including Listeria monocytogenes, Clostridium perfringens, Bacillus cereus and Staphylococcus aureus. Biochemical studies revealed that the bacteriocin was heat-stable even at autoclaving temperature (121 degrees C for 15 min) and was active over a wide pH range (2-10). The bacteriocin was inactivated by alpha-chymotrypsin and proteinase K but not other proteases. The antimicrobial spectrum and some characteristics of this bacteriocin were nearly identical to that of nisin. The gene encoding this bacteriocin was amplified by polymerase chain reaction (PCR) with nisin gene-specific primer. Sequencing of this gene showed identical sequences to nisin Z as indicated by the substitution of asparagine residue instead of histidine at position 27. The ability of the bacteriocin produced by Lc. lactis WNC 20 may be useful in improving the food safety of the fermented product.