A study of two isolated lactococcal strains with respect to bacteriocin-concentrations

Abstract

Lactococcus lactis strains present in wara (local cheese), and nunu (skimmed sour milk) were isolated. These were L.
lactis WO81 and N13L. Nisin assays were by agar diffusion test and turbidimetric assay. There was no successful
detection of an inhibition zone with wara. However, L. lactis strain WO81 from wara was able to produce nisin.
Exponential growth occurred for about 14 h after some lag phase. The optimum incubation time of 2 to 6 h was
established. Nisin concentration decreased with a subsequent increase in the incubation period. The effect of
inoculum size was found not to be conclusive but directional to an optimal size of 1.0% (V/V). The suitable working
temperature of 30oC and the pH value of 6 were discovered. Investigations into the phosphate sources revealed
KH2PO4 as the best phos-phate source. A physiological link is proposed between these functions, growth and nisin
concentra-tion. In the presence of sufficient glucose, growth was increased with the periodic addition of NaOH.
Maximum nisin concentration was obtained when, at pH 6, the medium was buffered. In this study essentially it is
noted that nisin has a lytic bactericidal mode of action.