Effect of bacteriocins produced by lactic acid bacteria from raniculture on the growth of pathogenic bacteria

S.E. PASTERIS; G. MONTEL MENDOZA; C.E. ALE; M.E. NADER-MACÍAS

Estambul

Congreso; 23rd INTERNATIONAL ICFMH SYMPOSIUM FoodMicro 2012; 2012

Lithobates catesbeianus (bullfrog) meat has a high proportion of essential amino acids, a large degree of absorbable proteins, low contents of NaCl and lipids (mainly cholesterol), according to the Food and Agriculture Organization. Thus, it is considered a delicacy by international gastronomy that has enhanced worldwide consumption. Intensive farming operations increase the risk of infectious diseases outbreaks, such as the red-leg syndrome (RLS). In our research group, Lactic Acid Bacteria (LAB) were isolated from the indigenous microbiota of Argentinean bullfrog hatcheries and some strains were selected as potentially probiotic to prevent RLS. Among them, Lactococcus lactis subsp. lactis CRL 1584 and Enterococcus gallinarum CRL 1826 are able to produce bacteriocins. In this work, the effect of the bacteriocins on the growth of indigenous RLS-related pathogens (Citrobacter freundii and Pseudomonas aeruginosa) and food-borne bacteria (Listeria monocytogenes Scott A) was determined. Previous assays indicate that L. lactis CRL 1584 produces 2,200 AU/mL of bacteriocin in LAPTg broth, active against L. monocytogenes, indigenous Lb. plantarum CRL 1651 and Ps. aeruginosa ATCC 27853. E. gallinarum CRL 1826 was grown in MRS broth and reached the stationary phase at 11h in microaerophilic conditions with an increase of 4 log10 viable cells. The pH decreased 1.6 units at 22h of incubation. The bacteriocin production against L. monocytogenes was associated to the growth, with the highest production level (61,440 AU/mL) at the end of the exponential phase. After 22h culture, the enterocin titre decreased to 25,600 AU/mL. The MIC and MBC were 2,640 and 5,280 AU/mL, respectively. L. monocytogenes was used as the indicator strain to evaluate the mode of action of both bacteriocins. A bactericidal effect was observed at 1 and 2,5h with E. gallinarum and L. lactis, respectively. Enterocin (120,000 AU/mL) evidenced a bacteriostatic effect against C. freundii and Ps. aeruginosa, while trypsin treated supernatants showed a bactericidal effect. These findings suggest that inhibitory peptides were released from the bacteriocin. The results indicate that both bacteriocins are excellent candidates to be included in the design of probiotic products and/or as carcases biopreservatives.