Occurrence of nisin Z production in Lactococcus lactis BFE 1500 isolated from wara, a traditional Nigerian cheese product

Screening for bacteriocin production of 500 strains of lactic acid bacteria (LAB) from various African fermented foods resulted in the detection of a bacteriocin producing Lactococcus lactis (BFE 1500) isolated from a dairy p roduct called wara. The bacteriocin inhibited not only the closely related LAB, but also strains of Listeria monocytogenes, Listeria innocua, Clostrid ium butyricum, Clostridium perfringens, Bacillus cereus and Staphylococcus aureus. It was heat stable even at autoclaving temperature (121 degrees C f or 15 min) and was active over a wide pH range (2-10), but highest activity was observed in the lower pH range. The bacteriocin was inactivated by alp ha-chymotrypsin and proteinase K, but not by other proteases. Growth kineti c assay indicated stronger growth inhibition by the bacteriocin produced by Lc. lactis BFE 1500 on L. monocytogenes WS 2250 and B. cereus DSM 2301 tha n with the nisin A producing strain DSM 20729. Polymerase chain reaction in dicated the presence of the nisin operon in strain BFE 1500 and sequencing of its structural gene showed that Lc. lactis BFE 1500 produced the natural nisin variant, nisin Z, as indicated by the substitution of asparagine res idue instead of histidine at position 27. The genetic determinants for bact eriocin production in strain BFE 1500 are located on a conjugative transpos on. The ability of the bacteriocin produced by Lc. lactis BFE 1500 to inhib it a wide range of food-borne pathogens is of special interest for food saf ety, especially in the African environment with perennial problems of poor food hygiene. (C) 1999 Elsevier Science B.V. All rights reserved.