Phylogenetic background and virulence genotype of ciprofloxacin-susceptible and ciprofloxacin-resistant Escherichia coli strains of human and avian origin.

Background: Previous studies have suggested that fluoroquinolone-resistant strains of Escherichia coli that infect humans probably emerged as a consequence of using fluoroquinolones in poultry. This study aims to provide further insight into the possible avian origin of fluoroquinolone-resistant extraintestinal pathogenic E. coli (ExPEC) strains that infect humans.

Methods: We compared the phylogenetic backgrounds, virulence gene profiles, and genetic relatedness of 125 ExPEC strains recovered from humans (61 were ciprofloxacin susceptible and 64 were ciprofloxacin resistant) and 113 E. coli strains recovered from poultry (47 were ciprofloxacin susceptible and 66 were ciprofloxacin resistant).

Results: Ciprofloxacin-resistant strains of both human and avian origin harbored fewer virulence genes than did ciprofloxacin-susceptible strains, but ciprofloxacin-resistant strains from humans were found to be clearly distinct from ciprofloxacin-resistant avian strains, based on their phylogenetic backgrounds and virulence gene profiles. The phylogenetic background of ciprofloxacin-susceptible and ciprofloxacin-resistant strains of human origin was not different, and no shift from the phylogenetic group B2 toward other groups was detected in association with ciprofloxacin resistance. No genetic relatedness was observed among human and avian strains that belonged to the major virulence profile (traT-iucD-iutA).

Conclusions: Our results did not support the hypothesis of an avian origin for the ciprofloxacin-resistant human ExPEC strains analyzed. Nevertheless, prudent use of fluoroquinolones in both human and veterinary medicine is recommended.