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 70,000 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.

Production of the antimicrobial peptides Caseicin A and B by Bacillus isolates growing on sodium caseinate.

AIMS: The aim of this study was to identify Bacillus isolates capable of degrading sodium caseinate and subsequently to generate bioactive peptides with antimicrobial activity. METHODS AND RESULTS: Sodium caseinate (2.5% w/v) was inoculated separately with 16 Bacillus isolates and allowed to ferment overnight. Protein breakdown in the fermentates was analysed using gel permeation-HPLC (GP-HPLC) and screened for peptides (<3-kDa) with MALDI-TOF mass spectrometry. Caseicin A (IKHQGLPQE) and caseicin B (VLNENLLR), two previously characterized antimicrobial peptides, were identified in the fermentates of both Bacillus cereus and Bacillus thuringiensis isolates. The caseicin peptides were subsequently purified by RP-HPLC and antimicrobial assays indicated that the peptides maintained the previously identified inhibitory activity against the infant formula pathogen Cronobacter sakazakii. CONCLUSIONS: We report a new method using Bacillus sp. to generate two previously characterized antimicrobial peptides from casein. SIGNIFICANCE AND IMPACT OF THE STUDY: This study highlights the potential to exploit Bacillus sp. or the enzymes they produce for the generation of bioactive antimicrobial peptides from bovine casein.

Lack of Heterogeneity in Bacteriocin Production Across a Selection of Commercial Probiotic Products.

Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit to the host. Bacteriocin production has often been mooted as a desirable probiotic trait and, in specific cases, has been shown to promote probiotic survival within the gastrointestinal tract, contribute to the control of pathogens and even influence host gene expression in the gut. However, it is not clear what proportion of probiotic strains routinely found in commercial products produces bacteriocins, and additionally, it is not known which bacteriocins are produced most frequently. To address this, we conducted a culture-based assessment of the bacteriocinogenic ability of bacterial strains found in a variety of commercially available probiotic products. We detected eight bacteriocin-producing isolates from 16 tested products. Interestingly, in all cases, the isolates were Lactobacillus acidophilus, and the bacteriocin produced was identified as the narrow spectrum class II bacteriocin, lactacin B. The apparent absence of other bacteriocin-producing strains from across these products suggests a lack of heterogeneity in bacteriocin production within probiotic products and suggests that bacteriocin production is not being optimally harnessed as a probiotic trait.