Avian colibacillosis is severe respiratory and systemic disease caused by avian pathogenic E. coli (APEC). The disease results in economic loss because of early mortality and reduced productivity in chickens. Several antimicrobials have been used extensively for reducing the losses due to colibacillosis. β-lactams, including penicillin derivatives, cephalosporins, and carbapenems, are one of the most commonly used, clinically important antibiotics. In this study, the phenotypic and genotypic characteristics of 14 CTX-M-producing APEC were investigated. Two types of CTX-M genes were detected, namely, CTX-M-1 gene (8 isolates) and CTX-M-15 gene (6 isolates), and all CTX-M-producing APEC were multidrug resistant. Moreover, 10 of the 14 CTX-M-producing E. coli isolates carried the TEM-1 gene, and 8 of the 14 isolates contained class 1 integrons. The following three different gene cassette arrangements were identified in six isolates: aadA1 (n=2), dfrA1 (n=2), and aadA1+dfrA1 (n=2). All CTX-M-producing APEC isolates harbored IncF plasmids, including F, FII, FIA, and FIB. CTX-M-1 gene was located on I1, F, and FIB, and CTX-M-15 gene on FII, FIA, and FIB. The findings from this study indicate that E. coli carrying CTX-M gene are circulating in the broiler poultry industry. Comprehensive surveillance and persistent monitoring of the integrated broiler operations are warranted to prevent the dissemination of resistant isolates.

Colibacillosis, which is caused by Escherichia coli (E. coli), is one of the most common infectious diseases affecting poultry and causes the great economic losses to poultry production worldwide. The present study investigated the presence of E. coli in broiler chickens affected by colibacillosis and reared at various locations in Tiaret Province as well as evaluated the susceptibility of isolated E. coli strains to various antimicrobial agents. A total of 110 samples collected from 55 broiler chickens representing liver (n=55) and spleen (n=55) showing lesions suspected to be colibacillosis were analyzed by conventional methods, and 33 E. coli isolates were tested on a panel of seven antimicrobial agents using the disk diffusion method. The overall isolation rates of E. coli were 60% (33/55) and 50.9% (56/110) in whole chickens and organs, respectively. There was no variation in the isolation rate between organs: 50% (28/56) for liver and 50% (28/56) for spleen. All E. coli isolates tested showed 100% resistance to Nalidixic acid and Ofloxacine, followed by 93.93%, 90.90%, and 51.51% resistance to Tetracycline, Trimethoprim-sulfamethoxazole (Co-trimoxazole), and Chloramphenicol, respectively. However, low resistance to Gentamycin was observed (12.12%), whereas all E. coli isolates were susceptible to Colistin sulfate. Multidrug resistance was observed in 96.96% (32/33) of the isolates tested. We conclude that E. coli was largely present in broiler chickens affected by colibacillosis in Tiaret Province, and multidrug-resistant E. coli isolates showed high resistance to multiple antibiotics.