Antibiotic resistance of Escherichia coli strains isolated from broiler chickens- Emergence of ESBL/AmpC strains in the Sfax governorate
Ben Salem Amenia, Ben Chehida Fatenb, Wafa Tombari, Nadia Jaziri, Dhahbia Bouceffa, Messadi Liliab

a Centre National de veille Zoosanitaire, Tunis
b École Nationale de Médecine Vétérinaire, Sidi Thabet, Tunis

Antimicrobial resistance is a worldwide threat to human, animal, and environmental health. This critical situation has been amplified by the intensification of livestock farming, especially for poultry, and antibiotic overuse. Among the resistant bacteria, Escherichia coli has become the main host for beta-lactamases. The latter are linked to a phenotype of resistance to diverse antibiotics classes that cause serious therapeutic failures.

The objectives of this study were to (i) determine the prevalence of E. coli digestive carriage in broiler chickens raised in the Sfax region, (ii) measure antibiotic resistance rates of the isolates and (iii) identify the major genes involved in β-lactams and colistin resistance.

A total of 139 E. coli strains isolated from cloacal swabs of broiler chickens aged 38-46 days and collected between February and May, 2019 from four farms in different regions of the Sfax governorate were studied. The susceptibility of E. coli strains to 21 antibiotics was investigated using the agar diffusion method. The presence of genes encoding for beta-lactams, cephalosporinases, and colistin resistance was determined by molecular analysis. Phenotyping results revealed the presence of 127 multidrug-resistant E. coli isolates (91.4%) and significant levels of extended spectrum b-lactamase (ESBL) (54%) and AmpC cephalosporinase (22.3%). High resistance rates were observed for tetracycline (99,3%), nalidixic acid (94.2%), cefuroxime (90.6%), amoxicillin (89.9%), enrofloxacin (89.2%), piperacillin (85.6%) and cefalotin (85.6%). Several tested strains (25.9%) were resistant to colistin, a last-resort antibiotic used in human medicine. Moreover, 2.9% of the strains were resistant to ertapenem, an antibiotic not used to treat animals. 

Molecular analysis of beta-lactams resistance genes was positive for blaCTX-M-1 (62), blaCTX-M-9 (6), blaSHV (2), blaTEM (2), and the cephalosporinase genes blaCMY (26) and blaAmpC (5). All C3G-resistant isolates (ESBL and cephalosporinases) tested positive for the mcr-1 plasmid gene, representing a prevalence of 25.2%.

These alarming results confirm the significant need for rigorous control of antimicrobial use, education of veterinarians about the risk of antibiotic resistance development and of livestock producers regarding the potential hazards of self-medication, an expanded laboratory monitoring of antibiotic resistance, and a follow-up to enable timely implementation of corrective measures.