Anti-microbial resistance is a matter of threat in global public health nowadays as a great number of antibiotics have lost their potential. In this study, we tried to characterize the tetA gene that was involved in tetracycline resistance of Escherichia coli (E. coli) in colibacillosis affected calves. To perform the study, a total of 69 fecal samples from colibacillosis suspected diarrheic calves were collected randomly from different areas of Rangpur division in Bangladesh. Standard laboratory protocols were followed for isolation and identification of E. coli. Then bacterial sensitivity was tested by culturing the bacteria in Mueller Hinton agar by following the protocol of Kirby-bauer disc diffusion method. Tetracycline resistant gene was specified by using tetA primer by searching tetA gene and the resistant gene was sequenced by sanger sequencing method. A phylogenetic tree of nucleotide sequences of tetA gene of E. coli was formulated using NCBI blast to characterize the gene. From 69 fecal samples, 54 were positive for E. coli. In antibiogram study, 100% isolates of E. coli were resistant to amoxicillin, ampicillin, cefoxitin, erythromycin and imipenem and the nature against others are as follows: doxycycline 64.8%, co-trimethoprim 63%, tetracycline 59.3%, ceftriaxone 50%, gentamicin 16.7%, levofloxacin 14.8% respectively. This study noticed, about 56.25% samples (18 from 32) were resistant to tetracycline due to tetA gene and the gene was closely related to the corresponding gene of Klebsiella pneumoniae, Shigella sonnei, Proteus mirabilis and Citrobacter braakii strains besides E. coli. This study suggests determining other genes specific for tetracycline resistance in E. coli of calves in Rangpur for better understanding the nature of it.
Key words: Colibacillosis, E. coli, Antibiotic resistance, Tetracycline, tetA gene, Phylogenetic tree
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