Identification and characterisation of antimicrobial activity of nisin a produced by Lactococcus lactis subsp. lactis LL27

Abstract

In this study, bacteriocin producing lactococcal strains were isolated from Turkish raw milk samples. Among these isolates, LL27 had the highest inhibition activity against Gram-positive indicator strains, and was selected for further analyses. DNA sequencing of 16S ribosomal RNA gene demonstrated that the isolate was Lactococcus lactis subsp. lactis. The gene encoding the bacteriocin in this strain was found to be identical to that of nisin A using direct PCR sequence methods. The bacteriocin was completely inactivated by α-chymotrypsin and proteinase K and partially inactivated by lipase and α-amylase. pH and heat stability characteristics were found to be identical with those of the control nisin. The inhibitory activity of the bacteriocin produced by LL27 was also evaluated against Gram-negative bacteria in combination with heat and freezing treatments. The results obviously showed that the production level of nisin of the Lc. lactis LL27 had a significant inhibitory effect on the pathogenic Gram-negative strains with the heating and freezing processes which are commonly used in the food processing.

Keywords

• nisin a
• lactococcus lactis
• sublethal injury
• heating
• freezing