Respiratory microbiota of healthy broilers can act as reservoirs for multidrug-resistant Escherichia coli

This study aimed at evaluate the presence and to study characteristics of Escherichia coli in the respiratory system microbiota of healthy broilers. Trachea, air sacs, and lungs of 20 broilers were analyzed at 21 days of age, reared in experimental conditions, without receiving antimicrobials. E. coli strains were isolated and identified using conventional bacteriology through morphological and biochemical characterization. The production of bacteriocin-like substances, the presence of virulence-associated genes (VAGs) of APEC (Avian Pathogenic Escherichia coli) predictors, and the antimicrobial susceptibility were evaluated. E. coli was found in 85 % of the animals (17/20), in the trachea, air sacs or lungs; and it was not found in 15 % of the animals (3/20). A total of 34 isolates were recovered, 13 from the air sacs, 13 from the lungs, and 8 from the trachea, which showed no production of bacteriocin-like substances nor virulence genes associated with APEC. Most isolates, 59 % (20/34), showed resistance to at least one of the tested antimicrobials, and six multiresistant strains were identified. The results demonstrated that strains of E. coli were commensal of the respiratory microbiota, and that they did not present pathogenicity to the host, since there were no clinical signs of disease, macroscopic lesions in the organs of the evaluated broilers, production of bacteriocin-like substances, nor virulence-associated genes considered as predictors of APEC in bacteria. These strains of E. coli were mostly susceptible to antimicrobials. However, the occurrence of multidrug-resistant strains suggests that these animals can act as reservoirs of resistant to antimicrobials E. coli.