Isolation of Escherichia coli O157:H7 from ground beef samples collected from beef markets, using conventional culture and polymerase chain reaction in Mashhad, northeastern Iran

  Escherichia coli O157:H7 is an important human pathogen causing haemorrhagic colitis, haemolyticuraemic syndrom and thrombotic thrombocytopenic purpura. In this study, 100 ground beef samples were collected randomly from beef markets in June 2004. For isolation of the bacteria, samples were firstly enriched in modified trypticase soy broth, followed by plating onto sorbitol MacConkey agar supplemented with cefixime and potassium tellurite. Consequently, the suspected non-sorbitol fermenting (NSF) colonies were confirmed by biochemical tests and employed for polymerase chain reaction (PCR) assay, using primers specific for O157 and H7 antigens gene. In this study, 7 NSF E. coli  colonies were isolated; in PCR assay only one of them confirmed as    E. coli  O157:H7. The PCR assay employed in this study may be a possible alternative to immunological assays which detects somatic and flagellar antigens.