Survival in acidic and alcoholic medium of Shiga toxin-producing Escherichia coli O157:H7 and non-O157:H7 isolated in Argentina

Growth at 37°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.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.Shiga toxin-producing E. coli (STEC) is now considered to be a common cause of haemorrhagic colitis (HC), haemolytic-uraemic syndrome (HUS) and thrombotic thrombocytopenic purpura in human [1].Argentina has an exceptionally high frequency of HUS, with 300 to 400 cases per year, and this is the most common cause of acute and chronic renal failure in young children [2-5]. HUS is considered a foodborne disease, early linked to consumption of hamburgers, ground beef and milk derivatives contaminated with STEC [6]. Bovine meat consumption in Argentina is estimated at 60 kg/habitant/year and is considered the highest reported in the world [3].In 1982, E. coli O157:H7 was isolated from hamburgers in the US and was considered as an etiologic agent of HC [7]. Since then, more than 100 serotypes of STEC have been isolated from animals and foods [8]. In Argentina, E. coli O157:H7 does not seem to be as common as in the US [3]. We have described many non-O157 strains, most of them isolated from cattle and foods [9].When food products serve as the vehicle of infections, the ingested inoculum ma