Escherichia coli O157:H7 isolated from feedlot-ground beef: bactericidal activity of AP-CECT7121 and synergistic effect with colistin

GARCIA ALLENDE L; DELPECH G; SPARO M; CECI M

Wrocław

Congreso; 14th International Congress of the European Association for Veterinary Pharmacology and Toxicology; 2018

European Association for veterinary Pharmacology and Toxicology

Introduction/Objective: The emergence of multidrug-resistant Escherichia coli strains highlights a need for new therapeutic options. But these bacteria remain globally sensitive to colistin. This antimicrobial is indicated for infections caused by Enterobacteriaceae in animal species that are used for livestock production, such as cattle. Toxic effects can be reduced using this drug combined with bacteriocins. In Argentina, feedlot systems have acquired a significant relevance as providers of meat products, such as ground beef. E. coli O157:H7 is one of the most important foodborne pathogens, with major implications in meat products industry. AP-CECT7121 is a bacteriocin produced by the probiotic strain Enterococcus faecalis CECT7121. In this study we aimed to investigate its bactericidal activity against E. coli O157:H7 isolated from feedlot-ground beef and the synergistic effect with colistin. Materials and methods: E. coli O157:H7 was isolated and characterized from feedlot-ground beef sold in markets in Tandil County (Argentina). Minimum Inhibitory Concentration (MIC) for AP-CECT7121, colistin and their combination against E. coli was assayed (micro-dilution method). In vitro bactericidal activity of AP-CECT7121 alone or combined with colistin (CIM/4), for assessing a synergistic effect, was studied carrying out time-kill curves. Samples were obtained for viable cell counts (0, 4, 8 and 24 h). MIC and time-kill curves were carried out three times. Results: AP-CECT7121 (MIC > 128 mg/L) alone not showed an inhibitory effect against E. coli; colistin presented anti-E.coli activity (MIC 0.3 mg/L). AP-CECT7121 combined with colistin showed bactericidal activity against E.coli (MIC 16/0.02 mg/L). A synergistic effect was observed at 4-8 and 24 h (-2.4 to -4.5 Δlog10 CFU/mL). Conclusions: AP-CECT7121 constitutes a candidate as a natural tool in combination with colistin, against E.coli O157:H7. Colistin increases the permeability of the cell membrane, allowing AP-CECT7121 to have a bactericidal effect against E.coli, which leads to lower MIC and toxicity for colistin.