Characterization of Shiga toxin-producing Escherichia coli O157:H7 isolated in Italy and in France

Abstract

Twenty-one Escherichia coli O157:H7 strains isolated in northern Italy from sporadic cases of hemolyticuremic syndrome and from cattle and food were characterized by virulence gene analysis, pulsed-field gel electrophoresis (PFGE) of XbaI-digested DNA, enterobacterial repetitive intergenic consensus (ERIC) sequence-based PCR (ERIC-PCR), and antibiotic resistance patterns and compared to 18 strains isolated in France from human cases of diarrhea, cattle, and the environment. Strains isolated in Sicily (southern Italy) from a local farm (one strain) and from calves just imported from France (11 strains) and Spain (six strains) were also typed. Whereas the eae and hlyA genes were always detected, Shiga toxin gene (stx) analysis showed some differences related to geographic areas. Isolates from northern Italy showed a high frequency of stx1 and stx2, while strains isolated in France and from French and Spanish calves imported to Sicily more frequently possessed the stx2c gene. The majority of the strains isolated in northern Italy were also resistant to one or more antibiotics, while most of the strains isolated in France and Sicily were fully susceptible. ERIC-PCR analysis was not able to differentiate the strains. PFGE typing after XbaI DNA digestion produced a total of 54 distinct restriction endonuclease digestion profiles (REDPs) among the 57 strains. Phylogenetic analysis was unable to cluster REDPs according to geographic origin. All epidemiologically related isolates showed either identical or ≥91% similar REDPs. Our findings suggest a peculiar circulation of antibiotic-resistant, genetically unrelated strains in northern Italy.