Molecular and phenotypic characterization of avian pathogenic Escherichia coli isolated from commercial broilers and native chickens

Many studies have examined avian pathogenic Escherichia coli (APEC) from commercial broilers but few have examined isolates from native chickens. This study compared APEC isolates from commercial broilers and native chickens in regard to the phylogenetic group and the phenotypic and genotypic antimicrobial resistance profiles. From 100 suspect colibacillosis cases in both commercial broilers and native chickens, a total of 90 broiler isolates and 42 native chicken isolates were identified as E. coli by biochemical tests. Phylogenetic grouping revealed that 90 broiler APEC isolates belonged to A group (5.56%), B1 group (22.22%), B2 group (31.11%), and D group (41.11%). The 42 native chicken APEC isolates belonged to A group (35.71%), B1 group (26.19%), B2 group (30.95%), and D group (7.14%). The difference in the allocation to groups A and D of the 2 isolate types was significant (P < 0.05). The APEC broiler isolates had a significantly higher multidrug-resistant (MDR) rate (80%) than the native chicken isolates (14.29%) (P < 0.05). The APEC broiler isolates demonstrated significantly higher resistance rates than the native chicken isolates for amoxicillin (98.89%; 78.57% respectively), chloramphenicol (42.2%; 9.5%), enrofloxacin (68.9%; 7.1%), gentamicin (11.1%; 0%), nalidixic acid (72.2%; 7.1%), sulfamethoxazole + trimethoprim (45.6%; 2.4%), and tetracycline (88.9%; 76.2%) (P < 0.05). The APEC broiler isolates had a significantly higher presence compared with the native chicken isolates of the following resistance genes:- by blaTEM (43.3%; 21.4%, respectively), cml-A (34.4%; 2.4%), tetA (76.7%; 40.5%), tetB (26.7%; 0%), sul2 (23.3%; 14.3%), and dhfrI (13.3%; 0%) (P < 0.05). The qnrB and qnrS genes were detected (12.16%; 72.97% respectively), in the APEC broiler isolates resistant to nalidixic acid and/or enrofloxacin while only qnrS genes was detected in all 3 APEC native chicken isolates. Regarding the point mutations of gyrA and parC, all isolates were positive to gyrA83S, gyrA87D, gyrA87L, gyrA87NY, parC80S and parC80I except that gyrA83S was not present in 20 APEC broiler isolates. Antimicrobial stewardship programs should be targeted at the backyard poultry sector as well as the commercial poultry sector.