Prevalence of Antibiotic Resistant E. coli Strains Isolated from Farmed Broilers and Hens in Greece, Based on Phenotypic and Molecular Analyses

The use of antimicrobials is beneficial for livestock health; however, their overuse and misuse may increase resistance to these compounds. Thus, the aim of the present study was the phenotypic and molecular examination of the presence of Escherichia coli antibiotic-resistant strains in broiler and laying hen farms. The resistance of E. coli strains was examined against various antibiotics, including several families of compounds such as penicillin class medications (ampicillin), cephalosporins (cefotaxime, cefoxitin, cefpodoxime and ceftazidime), sulfonamides (co-trimoxazole), quinolones (enrofloxacin and nalidixic acid), aminoglycosides (gentamicin), β-lactams (imipenem), aminoglycoside (streptomycin), and polymyxin (colistin). In total, 106 strains were investigated, sampled during the years 2016–2019 from 91 poultry farms, including 75 broiler farms and 16 laying hen farms, originating from three Regional Units in Greece. The examined isolates revealed the highest resistance rates to sulfamethoxazole (81.1%), nalidixic acid (73.6%), tetracyclin (70.8%), and streptomycin (70.8%). On the other hand, the resistance of the isolates to third generation cephalosporins was found to be at lower levels for ceftazidime (2.8%), ceftriaxone (3.7%) cefoxitin (4.7%), and cefotaxime (4.7%). Phenotypic tests showed that 13.6% and 10.2% of the isolates produced ESBL, while 2.7% and 1% produced AmpC b-lactamase, for broiler and laying hens, respectively. The prevalence of the mcr-1 gene was found to be 22.7%, detected only in broiler isolates. Based on our results, E. coli antibiotic resistance represents a critical control point in poultry production that, apart from farm animals, may affect public health as well.