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Title: Acid resistance and molecular characterization of Escherichia coli O157:H7 and different Non-O157 shiga toxin-producing E. coli serogroups

item KIM, GWANG-HEE - Kangwon National University
item Breidt, Frederick
item Fratamico, Pina
item OH, DEOG-HWAN - Kangwon National University

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2015
Publication Date: 10/1/2015
Publication URL:
Citation: Kim, G., Breidt, F., Fratamico, P.M., Oh, D. 2015. Acid resistance and molecular characterization of Escherichia coli O157:H7 and different Non-O157 shiga toxin-producing E. coli serogroups. Journal of Food Science. 80(10):M2257-M2264. doi: 10.1111/1750-3841.12996.

Interpretive Summary: Some disease-causing bacteria, such as Escherichia coli O157:H7 strains are very acid resistant. They can survive for a month or more is some acidic vegetable products. While acid adaptation has been investigated in a few of these strains, there is little knowledge of how acid resistance mechanisms work in real-world conditions, with the variety of different strain types of E. coli that may be present in acidic foods. This paper addresses the lack of knowledge. Our data show the mechanism(s) by which the acids in some juice products can increase survival and possibly increase the chance of disease from these potentially deadly bacteria. Knowledge of acid resistance and survival of these pathogenic strains in acid conditions is critical to developing an understanding of how best to prevent disease from acidic food products.

Technical Abstract: The objective of this study was to compare the acid resistance (AR) of non-O157 Shiga toxin-producing Escherichia coli (STEC) strains belonging to serogroups O26, O45, O103, O104, O111, O121, and O145 with O157:H7 STEC isolated from various sources in 400 mM acetic acid solutions (AAS) at pH 3.2 and 30 °C for 25 min with or without glutamic acid. Furthermore, the molecular subgrouping of the STEC strains was analyzed with the repetitive sequence-based PCR (rep-PCR) method using a DiversiLab^TM system. Results for a total of 52 strains ranged from 0.31 to 5.45 log reduction CFU/mL in the absence of glutamic acid and 0.02 to 0.33 CFU/mL in the presence of glutamic acid except for B447 (O26:H11), B452 (O45:H2), and B466 (O104:H4) strains. Strains belonging to serogroups O111, O121, and O103 showed higher AR than serotype O157:H7 strains in the absence of glutamic acid. All STEC O157:H7 strains exhibited a comparable DNA pattern with more than 95% similarity in the rep-PCR results, as did the strains belonging to serogroups O111 and O121. Surprisingly, the DNA pattern of B458 (O103:H2) was similar to that of O157:H7 strains with 82% similarity, and strain B458 strain showed the highest AR to AAS among the O103 strains with 0.44 log reduction CFU/mL without glutamic acid. In conclusion, STEC serotypes isolated from different sources exhibited diverse AR and genetic subtyping patterns. Results indicated that some non-O157 STEC strains may have higher AR than STEC O157:H7 strains under specific acidic conditions, and the addition of glutamic acid provided enhanced protection against exposure to AAS.