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Anti-Escherichia coli O157:H7 activity of free fatty acids under varying pH

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Following screening of 4 strains of Escherichia coli O157:H7 (E32511, E318N, H4420N, and R508N) for acid tolerance, strain H4420N was selected for further study into the influence of pH on bactericidal activity of 6 fatty acids (capric, lauric, palmitic, oleic, linoleic, and linolenic). Strain H4420N was cultured for 6 h in Luria-Bertani broth amended with individual fatty acids at 20 mmol/L, with pH adjusted to 7.0, 4.3, or 2.5. None of the fatty acids exhibited bactericidal activity at pH 7.0 (p >0.05). At pH 4.3, only capric, lauric, and linoleic acids reduced viability of H4420N (p < 0.05). At pH 2.5, oleic (C18:1) and linolenic (C18:3) acids had modest effects on H4420N viability, whereas capric (C10:0), lauric (C12:0), and linoleic (C18:2) acids resulted in a reduction >=5 log10 colony-forming units (CFU)/mL (p < 0.05). Capric and lauric acids were examined further at pH 2.5 over a range of concentrations (0.15-20 mmol/L). After 10 min of exposure, 5 log10 CFU/mL reductions (p < 0.05) were achieved by lauric acid at 2.5 mmol/L and by capric acid at 0.31 mmol/L. Acid stress increased the sensitivity of acid-tolerant E. coli O157:H7 strain H4420N to fatty acids. Including sources of these fatty acids in diets for cattle might impair the ability of this zoonotic pathogen to survive passage through the stomach, possibly reducing the potential for its colonization in the lower gut.

À la suite d’un examen de la tolérance acide de 4 souches d’Escherichia coli O157:H7 (E32511, E318N, H4420N et R508N), la souche H4420N a été choisie pour de plus amples études de l’influence du pH sur l’activité bactéricide de six acides gras (acides caprique, laurique, palmitique, oléique, linoléique et linolénique). La souche H4420N a été cultivée pendant 6 h dans le milieu Luria-Bertani amendé avec les acides gras individuels à une concentration de 20 mmol/L et dont le pH a été ajusté à 7,0, 4,3 ou 2,5. Aucun de ces acides gras ne montrait d’activité bactéricide à pH 7,0 (p > 0,05). Seuls les acides caprique, laurique et linoléique réduisaient la viabilité de H4420N (p < 0,05). À pH 2,5, les acides oléique (C18:1) et linolénique (C18:3) exerçaient de modestes effets sur la viabilité de H4420N, alors que les acides caprique (C10:0), laurique (C12:0) et linoléique (C18:2) réduisaient le nombre d’UFC/mL de >=5 log10 (p < 0,05). Les acides caprique et laurique ont été examinés davantage à pH 2,5 dans une gamme de concentrations (0,15 à 20 mmol/L). Après 10 minutes d’exposition, des réductions de 5 log10 du nombre d’unités formant colonie (UFC)/mL ont été obtenues avec l’acide laurique à 2,5 mmol/L et avec l’acide caprique à 0,31 mmol/L. Le stress acide a augmenté la sensibilité aux acides gras de la souche d’E. coli O157:H7 H4420N acido-tolérante. L’incorporation de sources de ces acides gras dans la diète du bétail pourrait diminuer la capacité de ce pathogène zoonotique de survivre au passage à travers l’estomac, réduisant possiblement son potentiel de colonisation dans le gros intestin.

Document Type: Research Article

Publication date: 2010-03-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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