Isolation and characterization of bacteriocin-producing bacteria from the intestinal microbiota of elderly Irish subjects

Aims: To isolate and characterize bacteriocins produced by predominant species of lactic acid bacteria from faeces of elderly subjects. Methods and Results: Screening over 70000 colonies, from faecal samples collected from 266 subjects, using the indicator organisms Lactobacillus bulgaricus LMG 6901 and Listeria innocua DPC 3572, identified 55 antimicrobial-producing bacteria. Genomic fingerprinting following ApaI digestion revealed 15 distinct strains. The antimicrobial activities associated with 13 of the 15 strains were sensitive to protease treatment. The predominant antimicrobial-producing species were identified as Lactobacillus salivarius, Lactobacillus gasseri, Lactobacillus acidophilus, Lactobacillus crispatus and Enterococcus spp. A number of previously characterized bacteriocins, including ABP-118 and salivaricin B (from Lact. salivarius), enterocin B (Enterococcus faecium), lactacin B (Lact. acidophilus), gassericin T and a variant of gassericin A (Lact. gasseri), were identified. Interestingly, two antimicrobial-producing species, not generally associated with intestinally derived microorganisms were also isolated: Lactococcus lactis producing nisin Z and Streptococcus mutans producing mutacin II. Conclusion: These data suggest that bacteriocin production by intestinal isolates against our chosen targets under the screening conditions used was not frequent (0·08%). Significance and Impact of the Study: The results presented are important due to growing evidence indicating bacteriocin production as a potential probiotic trait by virtue of strain dominance and/or pathogen inhibition in the mammalian intestine.