Biopreservation by bacteriocinogenic lactic acid bacteria in the control of Listeria monocytogenes in fresh cheese

Joint Conference on 6^th Annual Conference on Microbiology & Annual Conference on Microbes and Beneficial Microbes

October 16-17, 2017 Baltimore, USA

Svetoslav Dimitrov Todorov

Universidade Federal de Vi�§osa, Brazil

Posters & Accepted Abstracts: J Med Microb Diagn

Abstract :

It is well known that many lactic acid bacteria (LAB) are capable of producing a variety of antimicrobial compounds, which may contribute to their colonization of habitats and their competitive advantage over other bacteria. Besides production of lactic acid, which causes a drop in pH enough to inhibit certain strains, as its non-dissociated form triggers a lowering of the internal pH in sensitive bacteria that causes a collapse in the electrochemical proton gradient resulting in a bacteriostatic or bactericidal effect, LAB can produce other organic acids, diacetyl, hydrogen peroxide, and bacteriocins. Listeria monocytogenes is a pathogen frequently found in dairy products. Its control in fresh cheeses is difficult, due to the psychrotrophic properties and salt tolerance. Bacteriocinogenic LAB with proven in vitro antilisterial activity can be an innovative technological approach but their application needs to be evaluated by means of in situ tests. In addition, application of bacteriocinogenic strains for dairy product preservation is in agreement with consumersâ�� demands for foods that are naturally preserved. Several strains of Lactococcus spp and Enterococcus spp are capable of producing bacteriocins with antimicrobial activity against important bacterial pathogens in dairy products. The bacteriocins produced by L. lactis subsp. lactis DF04Mi and two Enterococcus strains (E. mundtii CRL35 and E. faecium ST88Ch), isolated from milk and cheeses, were characterized and tested for their capability to control growth of Listeria monocytogenes in experimentally contaminated fresh Minas cheese during refrigerated storage. Studied strains were active against a variety of pathogenic and nonpathogenic microorganisms and their auto-aggregation and co-aggregation with several Listeria monocytogenes, Enterococcus faecalis ATCC 19443 and Lactobacillus sakei ATCC 15521 varied according to the strain and the testing conditions (pH, temperature, presence of salts and surfactants). Growth of L. monocytogenes was inhibited in cheeses containing E. mundtii CRL35 up to 12 days at 8�°C, evidencing a bacteriostatic effect. L. lactis subsp. lactis DF04Mi and E. faecium ST88Ch was less effective, as the bacteriostatic affect occurred only after six days at 8�°C. In cheeses containing nisin (12.5 mg/kg), less than one log reduction was observed. This research underlines the potential application of E. mundtii CRL35 in the control of L. monocytogenes in Minas cheese.