Antimicrobial Resistance Phenotype and Genotype of Generic Escherichia coli from Encapsulated Cinnamaldehyde and Citral Fed-Broiler Chicken.

This study investigated the effects of in-feed encapsulated cinnamaldehyde (CIN) and citral (CIT) alone or in combination (CIN+CIT) on antimicrobial resistance (AMR) phenotypes and genotypes of E. coli isolated from feces of 6-, 16-, 23- and 27-days old broiler chickens. The five dietary treatments including the basal diet (control; NC), the basal diet supplemented with 55 ppm bacitracin (BAC), 100 ppm encapsulated CIN, CIT, or CIN+CIT. Antimicrobial susceptibility using a Sensititre method of 240 E. coli isolates showed that the most frequent resistances were against b-lactam, aminoglycoside, sulfonamide and tetracycline, however, the prevalence of AMR decreased (P < 0.05) when birds aged in general. The prevalence of resistance to amoxicillin-clavulanic acid, ceftiofur, ceftriaxone, cefoxitin, gentamicin, and sulfonamide was lower (P < 0.05) in isolates from CIN or CIN+CIT compared to those from NC or BAC. The whole-genome sequencing analysis of 227 of the 240 isolates detected 26 AMR genes (ARGs) and 19 plasmids but the prevalence of some ARGs and plasmid numbers were lower (P < 0.05) in E. coli isolated from CIN or CIN+CIT than NC or BAC. The most prevalent resistance genes included tet(A) (n=108), aac3_Vla (n=91), aadA1 (n=86), blaCMY-2 (n=78), sul1 (n=77), aph3_lb (n=58), aph6_ld (n=58), and sul2 (n=24). Interestingly, the number of most virulence genes (VGs) increased (P < 0.05) over time from 6 to 27 days of age. The prevalence of isolates of serotype O21:H16 was lower (P < 0.05) in CIN and CIN+CIT while colibacillosis-associated multi-locus sequence typing (ST117) was the most prevalent in isolates from day 23. A whole genome-based phylogenetic tree revealed a close relationship of 25 of 227 isolates to human or broiler extraintestinal pathogenic E. coli. This study indicates that AMR and virulence genotypes of E. coli could be modulated by encapsulated CIN or CIN+CIT feed supplementations and prompt further investigations on the involved mechanisms.