Phenotypical and genetic virulence and resistance in atypical avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli is a threat to poultry production systems, as it is associated with infections, poor production ratings, and economic losses. The spread of multidrug-resistant bacterial strains has aggravated the situation. Therefore, this study aimed to characterize 28 E. coli isolates from poultry farms in Brazil regarding virulence, as well as genetic and phenotypical resistance. Antimicrobial susceptibility test was carried out by the disk diffusion method, while the genomic information of the isolates was determined by whole-genome sequencing. Resistance was identified for all 19 antimicrobials tested, except imipenem. Elevated resistance was observed for rifampicin (96.4%) and oxacillin (67.9%); intermediate resistance for the carbapenems (ertapenem, meropenem, 10.7%), and tetracyclines (doxycycline, 10.7%) was also detected. Genotypic analyses showed that the most common resistance genes were tetA (39.3%) and gyrA (39.3%). Remarkably, the plasmid-mediated gene, MCR-1.1 , associated with colistin resistance, was detected in two isolates. The isolates tested did not carry the typical avian pathogenic E. coli genetic virulence panel; however, they presented great genetic diversity with prominent pathogenic potential connected to mechanisms of adhesion ( fimH , 96.4%), immune evasion ( ompA and ibeB/C , 100%; traT , 92.9%), and iron acquisition ( febB , 100%; iroN , 60.7%). The overlap between genotypic and phenotypic information emphasizes the health risk imposed by such atypical strains and their dispersion capability amongst both animals and humans. Our findings contribute to a better understanding of the diversity of avian pathogenic E. coli and reinforce the importance of combined diagnostic and surveillance strategies in the control of such bacteria.