Preliminary characterization of antimicrobial substances produced by lactic acid bacteria isolated from regional meat products

C. HERMAN; N. PALAVECINO; E. CAYRÉ; M. CASTRO; P. CASTELLANO

Tucuman Argentina

Simposio; III Simposio Internacional de Bacterias Láctica. Segundo Encuentro de la Red Argentina de Bacterias; 2009

CERELA

Lactic acid bacteria (LAB) have the potential to be used in biopreservation due to their ability to produce several antimicrobial substances including bacteriocins. The objective of the current study was to isolate LAB with potential use for the enhancement of the microbiological safety of meat products. LAB were isolated from a total of 8 regional meat products from the Chaco province. The antimicrobial activity was determined by the agar well diffusion assay (AWDA), using Listeria innocua 7 and Staphylococcus aureus FBUNT as indicator microorganisms. Cell-free supernatants were neutralized with NaOH to rule out a possible inhibitory action due to acid production as well as treated with catalase, proteinases (pepsin, papaín and protease XIV) and different temperatures (70 ºC for 15 min; 85 ºC for 15 and 30 min; 100 ºC for 15 min). The pH influence on the antimicrobial effectiveness was evaluated adjusting the supernatants to 3.5, 4.5, 5.5 and 6.5. From the 8 different meat products, 234 strains were isolated; seven of them exhibiting antimicrobial activity against both indicator microorganisms. These isolates were able to grow at refrigerated conditions and salt concentrations up to 6% w/w. Complete inactivation or significant reduction of the antimicrobial activity was observed after treatment of cell-free supernatants with proteinases. No change in activity was recorded when treated with catalase or NaOH. These results evidence the protein nature of the antimicrobial compounds produced by the selected strains. In all cases, bacteriocins production started in the mid-exponential growth phase, reached a maximum in the early stationary phase, remained constant and then declined, reflecting primary metabolite kinetics. The antimicrobial activity was stable after the application of different temperatures except for one cell-free supernatant which showed a decrease in the bactericidal effect after 15 min at 100 ºC. The inhibitory action against both indicator microorganisms was not affected at pH values of 3.5 and 4.5 obtaining the maximal bacteriocin activity; tree of the producer strains showed a decreased activity at pH 5.5 while all of them were inactive at pH 6.5. It can be concluded that LAB strains from meat products exhibiting antimicrobial activity against pathogenic microorganisms and able to grow at low temperatures and under 6% NaCl concentration constitute a promising biopreservatives in the prevention of food-borne illnesses.