title: Survival in acidic and alcoholic medium of Shiga toxin-producing Escherichia coli O157:H7 and non-O157:H7 isolated in Argentina.
abstract: BACKGROUND
  In spite of Argentina having one of the highest frequencies of haemolytic uraemic syndrome (HUS), the incidence of Escherichia coli O157:H7 is low in comparison to rates registered in the US. Isolation of several non-O157 shiga toxin-producing Escherichia coli (STEC) strains from cattle and foods suggests that E. coli O157:H7 is an uncommon serotype in Argentina. The present study was undertaken to compare the survival rates of selected non-O157 STEC strains under acidic and alcoholic stress conditions, using an E. coli O157:H7 strain as reference.
  
  
  RESULTS
  Growth at 37 degrees C of E. coli O26:H11, O88:H21, O91:H21, O111:H-, O113:H21, O116:H21, O117:H7, O157:H7, O171:H2 and OX3:H21, was found to occur at pH higher than 4.0. When the strains were challenged to acid tolerance at pH as low as 2.5, viability extended beyond 8 h, but none of the bacteria, except E. coli O91:H21, could survive longer than 24 h, the autochthonous E. coli O91:H21 being the more resistant serotype. No survival was found after 24 h in Luria Bertani broth supplemented with 12% ethanol, but all these serotypes were shown to be very resistant to 6% ethanol. E. coli O91:H21 showed the highest resistance among serotypes tested.
  
  
  CONCLUSIONS
  This information is relevant in food industry, which strongly relies on the acid or alcoholic conditions to inactivate pathogens. This study revealed that stress resistance of some STEC serotypes isolated in Argentina is higher than that for E. coli O157:H7.
authors.affiliation: Laboratorio de Inmunoquímica y Biotecnología, Animal Health Department, Universidad Nacional del Centro-CIC, Tandil (7000), Argentina. pablo-m@vet.unicen.edu.ar
authors.forename: Pablo M
authors.initials: PM
authors.lastname: Molina
authors.forename: Alberto E
authors.initials: AE
authors.lastname: Parma
authors.forename: Marcelo E
authors.initials: ME
authors.lastname: Sanz
mesh_terms: D000143:Acids / Q000494:pharmacology; D001118:Argentina; D003470:Culture Media / Q000737:chemistry / Q000494:pharmacology; D019453:Escherichia coli O157 / Q000737:chemistry / Q000187:drug effects*; D000431:Ethanol / Q000494:pharmacology*; D005516:Food Microbiology; D006863:Hydrogen-Ion Concentration; D022621:Shiga Toxin
chemical_list: D000143:Acids; D003470:Culture Media; D000431:Ethanol; D022621:Shiga Toxin