title: Survival and expression of acid resistance genes in Shiga toxin-producing Escherichia coli acid adapted in pineapple juice and exposed to synthetic gastric fluid.
abstract: OBJECTIVE
  The aim of this research was to determine the ability of non-O157 Shiga toxin-producing Escherichia coli (STEC) serogroups to survive with exposure to synthetic gastric fluid (SGF) after adaptation to pineapple juice (PJ) at room and refrigerated temperatures compared to E. coli O157:H7 and to examine the relative transcriptional expression of acid resistance (AR) genes, rpoS, gadA and adiA.
  
  
  RESULTS
  Resistant and sensitive strains belonging to five different STEC serogroups (O26, O103, O104, O111 and O157; n = 10) were used in this study. All strains were adapted in PJ (pH 3·8) stored at 4 and 20°C for 24 h, and then the relative transcription levels of genes in all strains were quantified using a real-time quantitative-PCR assay. After adaptation in PJ, the STEC strains were exposed to SGF (pH 1·5 and 2·0) at 37°C for 2 h. Generally, the STEC adapted in PJ at 4°C displayed enhanced survival compared to acid adaptation in PJ at 20°C and nonadapted controls with exposure to SGF (P < 0·05). Moreover, resistant strains exhibited higher survival rates compared to sensitive strains (P < 0·05). Overall, adaptation at 4°C resulted in significantly (P < 0·05) enhanced gene expression levels in PJ, and transcript levels of gadA were higher than those of the rpoS and adiA genes.
  
  
  CONCLUSIONS
  The up-regulation of AR genes due to adaptation in PJ at low temperature may increase STEC survival in acidic environments such as the gastrointestinal tract. Some non-O157 STEC strains, including serotypes O103:H2 and O111:H8, showed relatively high AR levels similar to those of STEC O157:H7.
  
  
  CONCLUSIONS
  Induction of AR genes in acidic fruit juice, and potentially in other acidic foods may increase the risk of foodborne illness by non-O157 STEC serogroups.
authors.affiliation: Department of Food Science and Biotechnology, Kangwon National University, Chuncheon, Gangwon, South Korea.|USDA-ARS Eastern Regional Research Center, Wyndmoor, PA, USA.
authors.forename: G-H
authors.initials: GH
authors.lastname: Kim
authors.affiliation: USDA-ARS Eastern Regional Research Center, Wyndmoor, PA, USA.
authors.forename: P
authors.initials: P
authors.lastname: Fratamico
authors.affiliation: USDA-ARS Food Science Research Unit, Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, NC, USA.
authors.forename: F
authors.initials: F
authors.lastname: Breidt
authors.affiliation: Department of Food Science and Biotechnology, Kangwon National University, Chuncheon, Gangwon, South Korea. deoghwa@kanagwon.ac.kr.
authors.forename: D-H
authors.initials: DH
authors.lastname: Oh
mesh_terms: D000222:Adaptation, Physiological; D031230:Ananas; D000818:Animals; D019453:Escherichia coli O157 / Q000235:genetics / Q000502:physiology; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D000067030:Fruit and Vegetable Juices; D005744:Gastric Acid; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D050296:Microbial Viability; D065288:Serogroup; D054323:Shiga-Toxigenic Escherichia coli / Q000145:classification / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic; D015854:Up-Regulation
chemical_list: D029968:Escherichia coli Proteins
keywords: Shiga toxin-producing Escherichia coli; acid resistance; gene expression; pineapple juice; real-time quantitative-PCR; synthetic gastric fluid