In vitro detection and characterization of bacteriocin-like inhibitory activity of lactic acid bacteria (LAB) isolated from Senegalese local food products

The prevalence of lactic acid bacteria (LAB) in Senegalese local food products was determined to be 109 CFU/g in millet flour and milk products, and 103 CFU/g in seafood products. These food products are generally preserved by spontaneous fermentation (without addition of starters). Of 220 lactic acid bacteria strains randomly selected from such products, 12 isolates capable of producing bacteriocin-like substances (bac+) were detected. Based on the use of API 50 CH test kits and 16S rDNA sequencing, 11 isolates were characterized as Lactococcus lactis subsp. lactis strains and one as an Enterococcus faecium strain. Nisin- and enterocin B-encoding genes were respectively identified in the bac+ lactococcal strains and the E. faecium strain. Since the bac+ Lc. lactis strains were isolated from different products, it suggests a high potential of growth by these strains in variable ecological environments. Expression of the nisin gene was indicated for one of the lactococcal strains, designated Lc. lactis subsp. lactis CWBI-B1410, which showed the highest in vitro antibacterial activity. An antibacterial preparation prepared from the CWBI-B1410 strain showed many similarities with nisin with regards to its inhibitory effects, heat resistance, protease sensitivity profile, as well as retention time of the antibacterial substances on a C-18 column. These results suggest that a nisin-like substance is produced by the CWBI-B1410 strain. This strain has been selected for application as an additional barrier to supplementation with sodium chloride as a means to improve the bacterial quality of fish commodities in Senegal.