Abstract

Cell-free supernatants (CFS) produced by 369 LAB strains previously isolated from fura and identified based on sequencing of their 16S rRNA genes were screened for their antagonistic activities against pathogenic bacteria including Bacillus cereus PA24, Escherichia coli SKN 541, Enterococcus faecalis 103907 CIP, Staphylococcus aureus ATCC 19095 and Listeria monocytogenes Scott A, using the agar well diffusion method. Bacteriocins of Lactobacillus reuteri 2-20B and Pediococcus acidilactici 0-11A were further evaluated for their stability when subjected to a range of pH conditions, enzymatic and heat treatments. Growth and bacteriocin production rates as well as influence of media composition on bacteriocin production were also evaluated. Cell free supernatants of Lb. reuteri and Pd. acidilactici strains exhibited the widest inhibitory activities whereas CFS of Lb. fermentum exhibited the least inhibitory activity towards the tested pathogens. Bacteriocins of Lb. reuteri 2-20B and Pd. acidilactici 0-11A retained their antibacterial activities over a wide range of pH. Whereas the antimicrobial activity of Lb. reuteri 2-20B was lost after being subjected to temperature of 90°C for 1 h, CFS of Pd. acidilactici 0-11A remained stable after autoclaving at 121°C for 15 min. Again, the antimicrobial activities of both Lb. reuteri 2-20B and Pd. acidilactici 0-11A were lost when the CFSs were subjected to the action of proteolytic enzymes but remained active under the actions of catalase, lipase and a-amylase. Production of bacteriocins by both Lb. reuteri 2-20B and Pd. acidilactici 0-11A were growth associated and influeced by media composition.

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