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Abstract: Lactic acid bacteria (LAB) antimicrobial peptides typically exhibit antibacterial activity against food-borne pathogens, as well as spoilage bacteria. Therefore, they have attracted the greatest attention as tools for food biopreservation. In some countries LAB are already extensively used as probiotics in food processing and preservation. LAB derived bacteriocins have been utilized as oral, topical antibiotics or disinfectants. Lactobacillus salivarius is a promising probiotic candidate commonly isolated from human, porcine, and avian gastrointestinal tracts (GIT), many of which are producers of unmodified bacteriocins of sub-classes IIa, IIb and IId. It is a well-characterized bacteriocin producer and probiotic organism. Bacteriocins may facilitate the introduction of a producer into an established niche, directly inhibit the invasion of competing strains or pathogens, or modulate the composition of the microbiota and influence the host immune system. This review gives an up-to-date overview of all L. salivarius strains, isolated from different origins, known as bacteriocin producing and/or potential probiotic. [Copyright &y& Elsevier]

t. ghrairi, m. manai, j.m. berjeaud and j. frère. 2004. Screening for lactic acid bacteria (LAB) producing bacteriocins and other antimicrobial compounds is of a great significance for the dairy industry to improve food safety. Six-hundred strains of LAB isolated from ‘rigouta’, a Tunisian fermented cheese, were tested for antilisterial activity. Eight bacteriocinogenic strains were selected and analysed. Seven of these strains were identified as Lactococcus lactis and produced nisin Z as demonstrated by mass spectrometry analysis of the purified antibacterial compound. Polymerase chain reaction experiments using nisin gene-specific primers confirmed the presence of nisin operon. Plasmid profiles analysis suggests the presence of, at least, three different strains in this group. MMT05, the eighth strain of this antilisterial collection was identified, at molecular level, as Enterococcus faecalis. The purified bacteriocin produced by this strain showed a molecular mass of 10 201·33 ± 0·85 Da. This new member of class III bacteriocins was termed enterocin MMT05. Seven lactococcal strains producing nisin Z were selected and could be useful as bio-preservative starter cultures. Additional experiments are needed to evaluate the promising strain MMT05 as bio-preservative as Enterococci could exert detrimental or beneficial role in foods. Only a few antibacterial strains isolated from traditional African dairy products were described. The new eight strains described herein contribute to the knowledge of this poorly studied environment and constitute promising strains for fermented food safety. [ABSTRACT FROM AUTHOR]

Abstract: Screening for bacteriocin production by strains of lactic acid bacteria from a Tunisian dairy product resulted in the detection of Enterococcus faecium bacteriocin producing strain. The anti-microbial compounds produced by this novel strain were heat stable and inactivated by trypsin, proteinase K and pronase E. Bacteriocins produced inhibited not only the closely related LAB, but also Listeria monocytogenes and Staphylococcus aureus. RP-HPLC purification of the anti-microbial compounds shows two individually active fractions eluted at 25.5 and 38.5min, respectively. Mass spectrometry analysis showed that E. faecium MMT21 produce two bacteriocins enterocin A (4828.67Da) and enterocin B (5463.8Da). This result was confirmed by amplification by PCR of enterocins A and B genes. The novel bacteriocin producing strain E. faecium MMT21 was not haemolytic, sensitive to vancomycin and other clinically relevant antibiotics and was an antilisterial strain. Therefore, it may be useful to improve the safety of fermented food products. [Copyright &y& Elsevier]

Abstract: Lactococcin MMT24 is a novel bacteriocin produced by Lactococcus lactis MMT24, a strain isolated from a Tunisian traditional cheese. The bacteriocin shows a narrow antimicrobial activity against closely related lactic acid bacteria. Lactococcin MMT24 is heat resistant, remains active after incubation at pH 3 to 10, lyophilization, long-term storage at −20 °C and is sensitive to treatment with proteolytic enzymes. The mode of action of lactococcin MMT24 was identified as bactericidal. Purification of the active compound showed that lactococcin MMT24 consists of two distinct peptides, named pepα and pepβ, whose complementary action is necessary for full antibacterial activity. Optimal antibacterial activity was obtained when the complementary peptides pepα and pepβwere present in equal amounts. Mass spectrometry analysis showed masses of 3765.33 Da and 3255.26 Da for pepα and pepβ, respectively. These molecular masses do not correspond to those of so far described bacteriocins. Addition of 50 nmol l−1 of lactococcin MMT24 to cells of L. lactis ssp. cremoris ATCC11603 induced increase in the concentration of K+ in supernatant indicating a massive leakage of this ion from the cells. This release was most likely caused by pores formation by the pepαand pepβ peptides in the target bacterial membrane. [Copyright &y& Elsevier]