Lactic acid bacteria biofilms and their ability to mitigate Escherichia coli O157:H7 surface colonization.

Lactic acid bacteria (LAB) exert antagonistic activities against diverse microorganisms, including pathogens. In this work, we aimed to investigate the ability of LAB strains isolated from food to produce biofilms and to inhibit growth and surface colonization of Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 at 10°C. The ability of 100 isolated LAB to inhibit EHEC O157:H7 NCTC12900 growth was evaluated in agar diffusion assays. Thirty-seven LAB strains showed strong growth inhibitory effect on EHEC. The highest inhibitory activities corresponded to LAB strains belonging to Lactiplantibacillus plantarum, Pediococcus acidilactici and Pediococcus pentosaceus species. Eighteen out of the 37 strains that showed growth inhibitory effects on EHEC also had the ability to form biofilms on polystyrene surfaces at 10°C and 30°C. Pre-established biofilms on polystyrene of four of these LAB strains were able to reduce significantly surface colonization by EHEC at low temperature (10°C). Among these four strains, Lact. plantarum CRL 1075 not only inhibited EHEC but also was able to grow in the presence of the enteric pathogen. Therefore, this strain proved to be a good candidate for further technological studies oriented to its application in food-processing environments to mitigate undesirable surface contaminations of E. coli.

A review of bacteriocinogenic lactic acid bacteria used as bioprotective cultures in fresh meat produced in Argentina.

Several lactic acid bacteria (LAB) associated with meat products are important natural bacteriocin producers. Bacteriocins are proteinaceous antagonistic substances that are important in the control of spoilage and pathogenic microorganisms. The use of LAB as bioprotective cultures to extend the shelf life of fresh meat can improve microbial stability and safety in commercial meat preservation. Lactobacillus curvatus CRL705 used as a protective culture in fresh beef is effective in inhibiting Listeria innocua and Brochothrix thermosphacta as well as the indigenous contaminant LAB, retaining its inhibitory effect at low temperatures and having a negligible effect on meat pH. In addition to the hurdle represented by low temperature and vacuum-packaging, the use of live cells of Lb. curvatus CRL705 seems more feasible from an economic point of view - and without legal restrictions - compared to the addition of purified bacteriocins. A description of meat-borne bacteriocins and their application in meat to extend shelf life is discussed.

Lactobacillus role during conditioning of refrigerated and vacuum-packaged Argentinean meat.

The role of Lactobacillus strains with bioprotective and technological potential on raw beef during 15days of storage under vacuum at 7°C was investigated. The assayed strains were able to grow on the meat, Lactobacillus curvatus CRL705 and Lactobacillus sakei 23K showing the highest competitiveness. A net increase of amino acids was determined in inoculated samples when compared to the control, this being maximal for Lactobacillus plantarum CRL681. Although an important endogenous activity of meat sarcoplasmic proteins was observed, the disappearance of protein bands and the generation of a new one were detected as a consequence of Lactobacillus growth. A synergistic effect of Lactobacillus in combination with the muscle proteolytic enzyme complex can be suggested. From the studied strains, the bacteriocin producer L. curvatus CRL705 may be considered as a good candidate to contribute to meat ageing by means of small peptides and free amino acids generation while improving shelf life.

Proteolytic activity of Lactobacillus strains isolated from dryfermented sausages on muscle sarcoplasmic proteins.

The proteolytic activity of seven strains of Lactobacillus from two species isolated from dry cured sausages was assayed using a soluble muscle extract as a source of proteins, at a temperature of 30 °C. The results indicated that the strains of Lactobacillus plantarum tested had the more active proteolytic system, showing the highest amino acid release in the medium after 72 hr of incubation (L. plantarum CRL 681) when the microorganism was in the stationary phase of growth. The strains of L. casei showed a continued hydrolytic activity with a lower amino acids concentration along the studied period. The SDS-PAGE profiles showed that the major changes in sarcoplasmic proteins were produced in the 13 kDa and 36-40 kDa molecular weights region.

Control of Listeria monocytogenes in ground beef by 'Lactocin 705', a bacteriocin produced by Lactobacillus casei CRL 705).

The effectiveness of Lactobacillus casei CRL 705 as well as that of Lactocin 705, the associated bacteriocin produced, in reducing population levels and growth of Listeria monocytogenes in sterile and non-sterile ground beef was studied. Predetermined numbers of L. monocytogenes and concentrations of Lactocin 705 were added to the meat slurries. Listeria in the bacteriocin-treated and control samples during incubation at 20 degrees C were enumerated as CFU on Bacto blood agar base. Results indicated that reduction in numbers of Listeria was largest with high levels of Lactocin 705 and few initial cell numbers of the pathogen present in the meat slurry. However, when the producer strain was added to the slurry, no significant inhibition was detected. Furthermore, inhibition by listeria was shown to be greater when meat slurries were heat-treated.