title: Recovery of E. coli O157 strains after exposure to acidification at pH 2.
abstract: OBJECTIVE
  Rapid detection and selective isolation of E. coli O157:H7 strains have been difficult owing to the potential interference from background microflora present in high background food matrices. To help selectively isolate E. coli O157H7 strains, a useful plating technique that involved acidifying the cultures to pH 2 was evaluated with a large number of E. coli O157:H7 strains to ensure response to treatment was consistent across strains.
  
  
  RESULTS
  Escherichia coli O157, 46 strains including ATCC 35150, were acidified to pH 2 following enrichment and plated onto Tryptic Soy Agar + 0.6% Yeast Extract (TSA-YE) and Sorbitol MacConkey Agar + cefixime and tellurite (CT-SMAC). Samples were enumerated and modest decreases in plate counts were observed on TSA-YE media, with a greater reduction observed on CT-SMAC.
  
  
  CONCLUSIONS
  The acid-resistant character of E. coli O157:H7 is a consistent trait and may be used for improved isolation of the organism from mixed cultures.
  
  
  CONCLUSIONS
  There was little difference observed between the commonly used laboratory strain E. coli O157:H7 35150 and 45 other strains of E. coli O157 when subjected to acidifying conditions prior to plating, demonstrating that an acid rinse procedure was equally effective across a wide variety of E. coli O157 strains and broadly applicable for isolating unknown strains from food samples.
authors.affiliation: Food and Drug Administration, Bothell, WA, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: Yoshitomi
authors.forename: R
authors.initials: R
authors.lastname: Zapata
authors.forename: K C
authors.initials: KC
authors.lastname: Jinneman
authors.forename: S D
authors.initials: SD
authors.lastname: Weagant
authors.forename: W
authors.initials: W
authors.lastname: Fedio
mesh_terms: D000143:Acids / Q000737:chemistry*; D000362:Agar / Q000737:chemistry; D001431:Bacteriological Techniques / Q000379:methods; D020682:Cefixime / Q000737:chemistry; D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005506:Food Contamination / Q000032:analysis; D005516:Food Microbiology / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D013012:Sorbitol / Q000737:chemistry
chemical_list: D000143:Acids; D003470:Culture Media; D013012:Sorbitol; D000362:Agar; D020682:Cefixime