Identification of bacteriocinogenic Lactococcus isolates from raw milk and cheese capable of producing nisin A and nisin Z

From a lactic acid bacteria culture collection obtained from raw milk and cheese, 27 isolates identified as Lactococcus spp. were studied to characterise their bacteriocinogenic activities. Twenty one isolates were PCR-positive for lantibiotic biosynthesis genes, and 18 of these were for the nisin gene. Twenty isolates were phenotypically identified as bacteriocinogenic, from which 18 also encoded lantibiotic biosynthesis genes and 13 for the nisin gene. The isolates presented wide inhibitory spectra, mainly against Listeria spp., and had their best antimicrobial performance when cultured in de Man, Rogosa and Sharpe (MRS) and modified MRS (0.5% dextrose) broths, incubated at either 25 °C for 24 h or 35 °C for 12 h. PCR products for the nisin gene from 8 isolates were sequenced, translated and compared with the nisin A sequence. Differences were observed in three isolates, indicating their capability of producing nisin Z variant. The findings suggest the potential use of these isolates as biopreservatives.