INTERACTION BETWEEN BIOPROTECTIVE LACTIC ACID BACTERIA AND ESCHERICHIA COLI O157: H7 DURING GROWTH AS PLANKTONIC CULTURES IN A MEAT BASED MEDIUM

ORIHUEL, A; G. VIGNOLO; SAAVEDRA L; FADDA S

CORDOBA

Congreso; XI CONGRESO ARGENTINO DE MICROBIOLOGIA GENERAL (SAMIGE); 2015

SAMIGE

The main cause of product recalls associated with fresh meat is contamination with Escherichia coli enterohemorrhagic (EHEC) and related enteric pathogens. In our country, hemolytic uremic syndrome, mainly caused by EHEC, is the most common cause of acute renal failure and the second cause of kidney transplantation in children. Therefore, EHEC is a serious threat to public health and a major concern for the sustainability of the meat industry. In addition, and considering the increased demand for food with high standards of hygiene and sensory quality, the search for solutions is imperative. In this context, the use Lactic Acid Bacteria (LAB) as bioprotective cultures is known and well documented for certain pathogens. However the efficiency of LAB and its metabolites to inhibit EHEC has been little explored.The aim of this study was to evaluate the inhibitory effect of bioprotective LAB strains on EHEC during incubation in a meat model system (MC). Four LAB strains, mostly isolated from meat products, with proven bioprotective properties were selected: Lactobacillus (L.) curvatus CRL 705; L. sakei CRL1862; Enterococcus (Ent.) mundtii CRL35 (isolated from artisan cheeses) and L. plantarum CRL 681. The pathogenic strain studied was Escherichia coli O157: H7 NCTC12900. This strain is a natural isolate which does not produce enterotoxins, but has intact other virulence factors.Each combination LAB-EHEC was evaluated by inoculating the MC with 106 CFU/ml of BL and 104 CFU/ml of E. coli and incubated under gentle stirring at 25 °C for 96 h. Samples were taken to analyze pH evolution and viability of both microbial groups using selective agar media. Previously to the study of LAB-pathogen interaction, the growth of each microorganism individually in MC under the same conditions was carried pout.The results showed good growth of LAB in the MC as pure cultures, the maximum viability was between 2,0.108 and 9,8.108 CFU/ml depending on the strains. When E. coli ATCC12900 was cultivated individually, an optimal growth curve in MC was observed reaching the stationary phase at 24 h (1,8.108 CFU/ml). When the co-cultures (LAB-EHEC) were analyzed, a decreased growth rate of LAB in the presence of EHEC was observed (1 to 2 log units less than in single culture condition), however their acidifying capacity was unaffected. Interestingly, the growth of the EHEC strain in co-culture was affected considerably. The strains CRL 681 and CRL 35 were able to totally reduce the population of E. coli during the time while the other analyzed strains showed variable inhibitory effects.Based on these results, we propose Ent. mundtii CRL 35 and L. plantarum CRL 681 as potential bioprotective strains capable to inhibit EHEC in meat environments. Currently, more detailed studies about the molecular mechanisms involved in the microbial interaction are in progress, in view to provide the meat industry with an efficient biotechnological solution to mitigate EHEC in meat products.