Evaluation of Antibiotic Resistance Pattern of Escherichia coli Isolated From Broiler Chickens With Colibacillosis in Ardabil Province, Iran

Introduction: Colibacillosis is one of the most important bacterial diseases of birds that is caused by Escherichia coli. This disease causes considerable economic damage to the poultry industry every year. Various antimicrobial agents are used to reduce the damage caused by this infection. But in recent decades, the increased use of antibiotics has led to the development of resistant genes and, consequently increasing antibiotic resistance of bacteria, leading to a decrease in the efficacy of antibiotics. The purpose of this study was to determine the susceptibility and drug resistance of 178 isolates of 40 chicken flocks in Ardabil province northwest of Iran. Methods: Five carcasses were randomly selected from each flocks with colibacillosis and sampled from liver and heart using sterile swabs. After culture and isolation, colonies were identified by biochemical and serological methods. Antibiotic resistance of all isolates to 19 antibiotics was determined using disk diffusion method based on CLSI guidelines. Results: Of 200 samples, 178 (89%) were isolated, and 22 (11%) did not grow. In this study the highest antibiotic resistance was observed against flumequine (98.31%), nalidixic acid (97.25%), tylosin (97.20%), oxytetracycline (97.20%), chlortetracycline (95.50%), difloxacin (89.32%), doxycycline (81.47%), enrofloxacin (77.53%), sulfamethoxazole + trimethoprim (71.91%), and the lowest antibiotic resistance was recorded for Linco-Spectin (36.52%), chloramphenicol (22.47%), gentamycin (7.30%), fuzbac (5.05%) and ceftriaxone (3.93%). All isolates were highly sensitive to ceftazidime. Conclusion: The results of this study showed a high level of resistance to antibiotics commonly used in poultry industry, which is probably due to improper use of antibiotics in poultries.