Distribution analysis of tetracycline resistance genes in fecal Escherichia coli isolated from sheep

BACKGROUND AND OBJECTIVESThere is a growing demand for livestock products and by-products due to an increase in the global human population. In this regard, the inappropriate use of antibiotics to enhance the growth of animals and reduce infectious diseases has led to the development of commensal and/or pathogenic bacteria resistant to antibiotics. One of these commonly used antibiotics is tetracycline. Escherichia coli (E. coli) is one of the important commensal bacteria with the ability to cause diseases, in which antibiotic resistance has been increasing worldwide. To better understand the selection pressures associated with the use of tetracycline in animal feed, the presence of six tetracycline resistance genes in fecal E. coli isolated from sheep was investigated.MATERIALS AND METHODSIn this study, ۳۰ stool samples were collected from sheep in Shiraz industrial slaughterhouse. All the samples were carefully placed in sterile containers and transferred to the microbiology laboratory as soon as possible. Samples were cultured on MacConkey agar medium and biochemical tests were performed to identify E. coli isolates. DNA of all confirmed E. coli isolates was extracted by boiling method, and polymerase chain reaction (PCR) assay was employed to evaluate the presence of tetA, tetB, tetC, tetD, tetK, and tetM genes in these isolates.RESULTS AND DISCUSSIONTetracyclines are antibiotics that are widely used in veterinary medicine; as a result, many bacteria - including E. coli - have become resistant to this drug. In the present study, ۲۴ fecal E. coli isolates were obtained from the sheep. Among them, ۱۵, ۵, ۱, ۰, ۱۴, and ۱۰ isolates had tetA, tetB, tetC, tetD, tetK, and tetM genes, respectively. Tetracycline resistance genes with the highest frequency were tetA (۶۲.۵%), tetK (۵۸.۳%), and tetM (۴۱.۷%), respectively. In contrast, the tetD gene was not found in any of the isolates.CONCLUSIONTetracyclines are valuable antibiotics in both human and veterinary medicine, but the emergence of bacterial resistance against them has reduced their therapeutic effect. The relatively high frequencies of tetracycline resistance genes in the fecal E. coli isolates of the studied sheep confirm this problem and the risk caused by the transmission of these resistant bacteria to humans.

کلیدواژه ها:

Antibiotic resistance ، Escherichia coli ، Tetracycline ، PCR ، Sheep