Virulence Genes Profile, Biofilm Formation, and Resistance to Disinfectant Agents in Avian Pathogenic <i>Escherichia coli</i> (APEC) Isolated from Broiler Farms

Background and Aim: Avian pathogenic Escherichia coli (APEC) is a major cause of colibacillosis in poultry, contributing to systemic disease and economic loss.This study investigated virulence genes profile, biofilm formation, and antimicrobial and disinfectant resistance in Escherichia (E.) coli isolates from broiler chickens in Qazvin, Iran.Materials and Methods: Liver samples were collected from 50 broiler chickens diagnosed with colibacillosis.Escherichia coli isolates were confirmed biochemically.Antibiotic susceptibility was evaluated using disk diffusion method, and virulence genes were detected via PCR.Biofilm formation was assessed using crystal violet staining.Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values for formaldehyde, glutaraldehyde, and hydrogen peroxide were determined using broth microdilution.Results: Among 50 isolates, 82% exhibited multidrug resistance (MDR) and 30% were extended-spectrum beta-lactamase (ESBL) producers.The most frequent and the least common genes were iss (66%), and papC (4%), respectively.All isolates formed biofilms, with 72% classified as strong producers.Formaldehyde and hydrogen peroxide exhibited the lowest MIC and MBC values ( 0.009%), while glutaraldehyde required higher concentrations for inhibitory and bactericidal activity (0.078%). Conclusion:High rates of MDR and biofilm formation among APEC isolates highlight the need for effective antimicrobial stewardship and disinfection strategies in poultry production systems.