Prevalence of tetracycline resistance determinants in broiler isolated Escherichia coli in Iran.

1. Tetracycline resistance determinants are widespread among bacterial species. Resistance to tetracycline occurs by different mechanisms regulated by various genes. 2. The study was conducted to determine the tetracycline resistance and prevalence of tetracycline resistance determinants among Escherichia coli strains isolated from broilers in northern Iran. 3. Minimum inhibitory concentration (MIC) of tetracycline and susceptibility pattern of the isolates were screened using micro-dilution and disk diffusion methods, respectively. The presence of 7 tetracycline resistance genes including tetA, tetB, tetC, tetD, tetE, tetG and tetM was tested using the polymerase chain reaction. 4. Among 100 strains isolated from broilers, 73% were identified as tetracycline resistant. All isolates showed the presence of tetracycline-associated genes. The most prevalent genes were tetA (46%) and tetB (41%) and totally, 17 different genotypes were recognised according to the presence of tetracycline resistance genes. Statistical analysis revealed that concomitant presence of the resistance genes significantly increased the tetracycline MIC and effectiveness of phenotypic characterisation. 5. The results demonstrated a high occurrence of tetracycline-resistant E. coli and related genes among broilers which presents a risk of increasing these strains in human infections associated with food animals.