Bio-control of Vibrio species in cultured milk by in situ bacteriocin production from lactic acid bacteria

The growth of resistance to antibiotic by Vibrio signifies a possible risk to human health; hence, there is a need to deploy another technique for controlling species of Vibrio. This study was undertaken to demonstrate the antagonistic activity of bacteriocin-producing Lactic acid bacteria against Vibrio alginolyticus, Vibrio vulnificus, Vibrio harveyi, Vibrio parahaemolyticus, Vibrio fluvialis, and Vibrio cholera in vitro and in situ. Lactic acid bacteria (LAB) were isolated from milk products and identified phenotypically. They were initially screened for antagonistic activity against the Vibrio species by the agar well diffusion assay, bacteriocins produced by the LAB were characterized with respect to pH, enzymes and temperatures. The effect of in situ bacteriocin production by LAB on the survival of Vibrio species was determined in Nono, after fermentation of milk during the storage period of 72 h (12 h interval). Of the 112 strains of LAB tested for antagonistic activity against Vibrio species, only twelve were selected based on the bacteriocin production and large zone of inhibition against Vibrio species. They were characterised phenotypically and identified to be Pediococcus damnosus, Pediococcus acidilactici, Lactobacillus brevis and Lactobacillus plantarum. The bacteriocins produced by the LAB were heat stable at 90°C for 20 min, active over a wide pH range (2 to 6), stable in the present of catalase but lost their activity in the present of proteolytic enzymes. Bacteriocins produced by the LAB showed antagonistic activity against Vibrio species with zones of inhibition ranges from 12 to 20mm. Vibrio species counts were reduced significantly to different extents in all samples of Nono and undetectable within 48 to 60 hours of Nono storage. On the contrary, Vibrio species survived for 72 h of storage in the control experiment that lack bacteriocin producing LAB. This work demonstrates that the use of selected bacteriocin-producing starter in milk fermentation might contribute to safety of dairy products.