Na. Olasupo et al., Occurrence of nisin Z production in Lactococcus lactis BFE 1500 isolated from wara, a traditional Nigerian cheese product, INT J F MIC, 53(2-3), 1999, pp. 141-152
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.