Antimicrobial Resistance and Virulence in Escherichia coli from Broilers: Genetic Insights for One Health

The widespread use of antibiotics in livestock has significantly contributed to the emergence and spread of antimicrobial-resistant bacteria, posing a risk for zoonotic transmission. The presence of multidrug-resistant Escherichia coli in poultry emphasizes the need for a One Health approach in monitoring antimicrobial resistance. This study aimed to determine the prevalence of E. coli in fecal samples from broilers, characterize their antimicrobial resistance profiles, and assess their genetic traits, including resistance genes, virulence factors, integrases, and phylogenetic groups.

Genomic DNA was extracted from 19 E. coli isolates obtained from broiler fecal samples collected at Savinor (Trofa, Portugal) using the boiling method. Resistance genes, integrases, virulence factors, and phylogenetic groups were identified by PCR. Only two isolates lacked resistance genes. The most prevalent gene was ampC (17/19), followed by tetA (12/19), blaCTX-M (11/19), and qnrS (7/19). Other detected genes included blaSHV, blaTEM, blaVIM, aadA1, aadA5, sul2, strB, sul1, blaIMP, and aac(3)-II. All isolates carried the fimA virulence factor, with five also harboring aer. The int1 integrase gene was found in six isolates. Phylogenetic analysis showed that 12 isolates belonged to group A, five to B1, and two to D.

This study reveals the high prevalence of antibiotic-resistant E. coli in broilers in Portugal, underscoring the importance of regional surveillance. The combined analysis of resistance, virulence factors, and phylogenetic groups provides a broader understanding of the genetic traits that may enhance zoonotic potential. Resistance was mainly observed in typically commensal phylogroups, suggesting an adaptation to selective pressure in poultry environments. Stronger antimicrobial stewardship, including restricting critically important antibiotics, promoting alternatives like probiotics and vaccination, and improving farm hygiene, is crucial. Future research should focus on tracking resistance gene mobility and transmission pathways to inform public health strategies within a One Health framework.