Vidhya Prakash

Bacteriocins from lactic acid bacteria (LAB) are natural antimicrobial peptides or proteins with potential applications in food preservation and healthcare. The study aimed at screening and characterization of bacteriocins from the secretome of five Lactobacillus strains. We were able to screen the antagonistic potential of two strains, L. fermentum and L. casei 335 against the multidrug resistant pathogens, Escherichia coli MDR (multidrug resistant) and Salmonella typhi isolated from sewage. Different dialysate fractions of the Lactobacillus strains were screened by soft agar diffusion and microtitre inhibition assay. Dialysate fractions from ammonium sulfate precipitate, at 65% (LF 65) and at 90% (LF 90) from L. fermentum were tested. LF60 (40μg/mL) was found to be inhibitory to the growth of E. coli MDR strain. Minimum Inhibitory Concentrations (MIC) against biofilm formation were found to be 40μg/mL for both E. coli MDR and Salmonella typhi, though inhibition was found at sub MIC of 20 μg/mL. Biofilm dispersal inhibition of E. coli MDR and S. typhi demonstrated a percentage inhibition rate of 50%. For initial characterization of the proteome of LAB strains, Tricine SDS-PAGE was performed which yielded a protein band of molecular size of 11 kDa from LF 60 fractions. Gel overlay assay showed an inhibitory effect on growth of E. coli MDR, indicating the presence of bacteriocin activity. Caenorhabditis elegans was employed as a nematode model to study the in vivo protection against E. coli MDR. Significant enhanced survival (91%) of the nematode was observed on treatment with LF 60. The efficacy of these partially purified preparations in inhibiting enteric pathogens showcase a prospective strategy of application of these antimicrobials in food and other environmental applications where cost of purification is of concern.