Lineages and Virulence Gene Content among Extended-Spectrum β-Lactamase-Producing Escherichia coli Strains of Food Origin in Tunisia

Nineteen extended-spectrum β-lactamase (ESBL)-positive Escherichia coli strains recovered from food samples in Tunisia were characterized by multilocus sequence typing and phylogenetic typing, and the virulence gene and plasmid content were also determined. These strains presented unrelated pulsed-field gel electrophoresis patterns and contained genes coding for the following ESBLs (the number of strains is in parentheses): CTX-M-1 (15), CTX-M-14 (2), CTX-M-8 (1), and SHV-5 (1). Twelve different sequence types (STs) were identified among the 19 ESBL-positive strains, which included two new STs (ST2022 in 2 bla CTX-M-14 -containing strains and ST1970 in 2 bla CTX-M-1 –containing strains). ST155 and ST602 were detected in four and three bla CTX-M-1 –containing strains, respectively, and ST405 was detected in one bla CTX-M-8 -producing strain. All ESBL-positive strains were ascribed to the phylogenetic groups A and B1. Most of the bla CTX-M-1 –containing strains harbored an IncI1 plasmid, except for the four bla CTX-M-1 –positive strains of beef origin and ST155, which harbored an IncN plasmid. The two bla CTX-M-14 -containing strains contained an IncI1 plasmid. The virulence gene fimA was detected in all strains. Most strains also carried the aer gene, and six strains carried the eae gene. All strains were negative for the virulence genes sxt, papG -III, papC, hly, cnf1, and bfp. We conclude that ESBL-producing E. coli strains of food origin in Tunisia show high diversity and that plasmids harboring ESBL genes could be implicated in the dissemination of this resistance phenotype.