Abstract
Colibacillosis is a disease caused by avian pathogenic Escherichia coli (APEC) isolates which results in significant morbidity and mortality in poultry, as well as in economic loses. In order to identify APEC strains in a population of 898 E. coli isolates from poultry samples collected from different avian flocks located in the Valencian Region, Spain, we analysed the most significantly related to highly-pathogenic colibacillosis virulence-associated genes (VAGs) (hlyF, iroN, iss, iutA and ompT) by multiplex real-time polymerase chain reaction (RT-PCR). Results from this study showed that 59.5 % of the strains were identified as APEC by the expression of the five VAGs. In addition, both phenotypic and genotypic resistances to the last-resort antibiotic colistin in the same population were detected through either antimicrobial susceptibility tests or RT-PCR targeting mcr-1 and mcr-2 genes. An expected low frequency of colistin-resistant E. coli strains was detected as well as a low but noteworthy proportion of 3.3 % extremely-drug resistant strains, which encourages to still reducing the use of antibiotics in animals and humans to prevent the transmission of antimicrobial resistances among them.