Introduction and Objectives Escherichia coli is the most frequently encountered gram negative organism causing diarrhea. The aim of this study was to determine the occurrence of enterotoxigenic E. coli (ETEC) strains and antibiotic resistance of the isolates in neonatal calves in Hamedan city. Materials and Methods A total of 120 rectal swab samples were collected from calves of 8 different industrial dairy farms in Hamadan city. Conventional bacterial isolation and polymerase chain reaction (PCR) were used in the evaluation and detection of ETEC isolates from samples, Additionally, antibiotic susceptibility patterns were determined in the isolates against antibiotics by disk diffusion method. Results Upon phenotypic and genotypic examinations, 23 (l9.l6%) samples were found to be positive for E. coli. 10 isolates were identified as ETEC giving positive amplicon for the virulence genes in ETEC. Antibiogram study revealed that the isolated ETEC was highly sensitive to Ciprotloxacin/ Trimethoprim Sulfamethoxazole/ Enrofloxain (100%) following by /Ceftriaxon/ (each 80%) and Chloramphenicol (70%), moderately sensitive to Gentamycin (l00%), Cefazolin(90%) and Tetracycline (80%) and Streptomycin (70%), while 100% resistant to Polymyxin B and Amoxi-clav. Conclusion Our Results exhibited multiple drug resistance in ETEC strains from calves and underline the importance of calves as reservoir of resistance genes which may transfer to human and other hosts, Furthermore, this level of resistance to antimicrobials might herald problems in the management of intra- and extra-intestinal infections caused by ETEC.
