Characterization of tetA gene of Escherichia coli isolated from colibacillosis affected calves in Rangpur, Bangladesh

Antimicrobial resistance is a matter of threat in global public health nowadays as a great number of antibiotics have lost their potential. The current study aimed to characterize the tetA gene involved in tetracycline resistance of Escherichia 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 of the isolates of E.coli against other antibiotics were as follows: doxycycline 64.8%, co-trimethoprim 63%, tetracycline 59.3%, ceftriaxone 50%, gentamicin 16.7%, levofloxacin 14.8% respectively. This study noticed that about 56.25% samples (18 from 32) were resistant to tetracycline due to tetA gene and the gene (tetA from E. coli) 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 the other genes that are specific for tetracycline resistance in E. coli in Rangpur for better understanding the nature of it.