Plasmid-Associated Bacteriocin Production in Lactobacillus Strains Isolated from Some Traditional Fermented Foods

Earlier report has shown the Lactobacilli isolates from some traditional fermented foods, LABB (appam batter) and LABP (vegetable pickle) to produce bacteriocins, inhibitory to a variety of spoilage and pathogenic organisms. In the present study, the plasmid profile, their curing and transformation experiments were carried out to deduce if the bacteriocins are plasmid mediated. Both the strains harbored multiple plasmids ranging in size from 1.5 kb to more than 10 kb. Plasmid curing trials showed that a combination of acriflavin, ethidium bromide and novobiocin could induce loss of plasmid DNA in these strains, 10 and 6 kb plasmids in LABB while only a single plasmid of 10 kb in LABP. They were resistant to ciprofloxacin, colistin, gentamycin, nalidixic acid and streptomycin while LABB was resistant to norfloxacin as well. The cured strains became sensitive to ciprofloxacin, gentamycin and streptomycin as well as to its bacteriocin. Plasmid curing resulted in loss of their ability to produce bacteriocins as evidenced by the absence of both the inhibitory activity against indicator organism, S. aureus and the bacteriocin band in SDS-PAGE clearly indicating that the bacteriocin production was plasmid mediated. This was also confirmed by the transformation of non-producing LAB with the eluted 10kb plasmid which elicited inhibitory activity against indicator organisms as well as presence of the bacteriocin band in SDS PAGE corresponding to that of native strains.