Phenotypic and Molecular Study of Multidrug-Resistant Escherichia coli Isolates Expressing Diverse Resistance and Virulence Genes from Broilers in Tunisia

This study investigated the molecular and phenotypic characteristics of antimicrobial resistance in <i>Escherichia coli</i> isolates recovered from the ceca of healthy broilers in Tunisia. A total of 111 <i>E. coli</i> isolates were obtained from chicken samples collected at slaughterhouses and cultured on cefotaxime-supplemented MacConkey agar. All isolates exhibited a multidrug-resistant (MDR) phenotype, and 72.1% were confirmed as extended-spectrum β-lactamase (ESBL) producers. The most frequent β-lactamase gene was <i>bl</i>a_CTX-M-G1, followed by <i>bla</i>_TEM and <i>bla</i>_SHV. Carbapenem resistance genes (<i>bla</i>_OXA-48 and <i>bla</i>_IMP) were detected in 12.6% and 6.3% of isolates, respectively, while six isolates harbored the colistin resistance gene <i>mcr-1</i>. Among the tested virulence genes, <i>fimH</i>, <i>traT</i>, and <i>iutA</i> were the most prevalent, detected in over 70% of isolates. Class 1 integrons were present in 83% of isolates, and class 2 integrons in 39.6%, with gene cassettes encoding resistance to trimethoprim (<i>dfrA</i>) and streptomycin (<i>aadA</i>). These findings highlight the widespread presence of MDR and ESBL-producing <i>E. coli</i> strains with virulence traits and integrons in poultry, underscoring the risk of transmission to humans. This study provides essential data supporting the implementation of integrated surveillance strategies in line with the One Health approach.