LACTOBACILLI STRAINS AND THEIR METABOLITES AS ANTAGONISTIC AGENTS OF Escherichia coli O157 AND NON-O157 GROWTH

ARSAUTE, SOFIA; ASURMENDI, PAULA; RUÍZ, FRANCISCO; GARCÍA, MA. JOSÉ; CAMILLETTI, ANA LISSA; PASCUAL, LILIANA; BARBERIS, LUCILA

Tucumán

Congreso; XII Congreso Argentino de Microbiología General; 2017

Sociedad Argentina de Microbiología General

Shiga-toxin producing Escherichia coli (STEC) is a major foodborne pathogen causing Hemolytic Uremic Syndrome (HUS), which is a severe human disease worldwide. Several serotypes are commonly associated with human diseases but E. coli O157:H7 is the most frequently isolated. Nowadays, lactobacilli have gained an increasing scientific interest as a biological option for the control of this pathogenic microorganism. The objective of this study was to evaluate the inhibitory activity of lactobacilli strains on E. coli O157:H7 and non-O157 strains. Six strains of bacteriocin-producing lactobacilli identified as L. fermentum L23, L. brevis L52, L. plantarum L54 and L57, L. cellobiosus L56, L. rhamnosus L60 were tested. Thirty STEC strains, serotypes H7:O157 (n=17) and non-O157 (n=13), were selected as indicator microorganisms. The antimicrobial activity of each lactobacilli strain was evaluated by two in vitro techniques, the streak-diffusion and well-diffusion methods. Firstly, a central streak of lactobacilli strain was seeded on an MRS agar plate and then different STEC were perpendicularly streaked. Plates were incubated in microaerobic conditions at 37°C for 24h. Average inhibition zones of bacterial growth were measured in mm. The inhibitory activities of different metabolites released by lactobacilli were tested by the well-diffusion method. Thus, two types of cell-free supernatant of lactobacilli growth, CFS and N-CFS, were obtained. CFS contains all produced metabolites (organic acid + bacteriocin), while the neutralized CFS (N-CFS) only contains bacteriocin. Six selected lactobacilli strains inhibited 100% of STEC strains. The average values of inhibition zones by the streak-diffusion method were 18.7 mm; 30 mm; 27 mm; 29 mm; 28 mm and 20.5 mm for L23, L52, L54, L56, L57 and L60 strains, respectively. By the well-diffusion method, the SLCs showed values of inhibition halos which ranged between 22 mm and 23.7 mm, being L. plantarum L57 the strain with higher inhibition activity. The supernatants maintained important antimicrobial action after neutralization treatment. The mean inhibition halos obtained with N-CFS on different STEC were 16.6 mm; 15.3 mm; 17.2 mm; 16.5 mm; 15.2 mm and 16.4 mm for L23, L52, L54, L56, L57 and L60 strains, respectively. It is important to highlight that the inhibition effect found was mainly due to the bacteriocins. In relation to the total antimicrobial activity, the inhibitory action specifically due to bacteriocins reached values between 65% and 75%. Among the STEC serotypes studied, the O157 strains were the most sensitive to both, CFS and N-CFS, in comparison to non-O157 strains. In conclusion, the thorough selection of these lactobacilli strains could represent a valuable biological strategy for control of shiga toxin-producing E. coli strains. Furthermore, future studies employing combinations of these strains could enhance their antimicrobial power.