title: Shiga toxin-producing Escherichia coli isolated from lettuce samples in tehran, iran.
abstract: BACKGROUND
  During the last decade, the prevalence of foodborne diseases due to contaminated food as well as the outbreaks of diseases due to Shiga toxin-producing Escherichia coli (STEC) strains has increased.
  
  
  OBJECTIVE
  The aim of this study was to evaluate the prevalence and antibiotic resistance pattern of STEC strains in lettuce samples. Since lettuce is used as a raw vegetable in salads, the rates of infections caused by this vegetable are high.
  
  
  METHODS
  A total of 100 samples collected from Tehran, Iran, were transported to the laboratory, homogenized by a stomacher in E. coli broth containing cefixime, and cultured on MacConkey agar medium. Their DNA was extracted by boiling method and polymerase chain reaction (PCR) was performed, using five primers targeting the stx1, stx2, fliCh7, rbfO157, and eaeA genes. Susceptibility testing against ampicillin, imipenem, cephalosporin, tetracycline, aminoglycosides, chloramphenicol and quinolones was performed using disk diffusion method.
  
  
  RESULTS
  Eight samples were positive for presence of STEC strains, three contained stx1, five contained stx2, and one sample was positive for presence of both rbfO157 and fliCh7. They were susceptible to all the antibiotics except for ampicillin and tetracycline.
  
  
  CONCLUSIONS
  This study indicated the contamination of lettuce by STEC strains and its possible role as the source of infection. Resistance to both tetracycline and ampicillin may be considered as an emergency alarm for a multidrug resistance of STEC strains.
authors.affiliation: Department of Biology, Alzahra University, Tehran, IR Iran.
authors.forename: Somayeh
authors.initials: S
authors.lastname: Mazaheri
authors.affiliation: Department of Biology, Alzahra University, Tehran, IR Iran.
authors.forename: Siavosh
authors.initials: S
authors.lastname: Salmanzadeh Ahrabi
authors.affiliation: Department of Microbiology, Pasteur Institute of Iran, Tehran, IR Iran.
authors.forename: Mohammad Mahdi
authors.initials: MM
authors.lastname: Aslani
keywords: Iran; Shiga toxigenic Escherichia coli