Antimicrobial Resistance Characteristics and Phylogenetic Groups of Escherichia coli Isolated From Diarrheic Calves in Southeast of Iran

Background: Antimicrobial resistance (AR) is one of the main challenges in diarrheal diseases in human and animals. Regardless of the main reason of the disease, approximately all antimicrobial actions including treatment, control, and prevention are mostly centralized against Escherichia coli strains. Objectives: This work was focused on AR and determination of phylogenetic groups in E. coli isolates (n = 170) obtained from calves with diarrhea. Materials and Methods: Isolates were molecularly characterized for 17 AR genes and 3 phylogenetic sequences. AR phenotyping was performed on all strains for 12 antimicrobial agents by using disc diffusion method. Results: All AR genes but qnrS were identified with different prevalence in E. coli isolates; the most common genes were aadA (20%), blaTEM (11.7%), and sulII (11.2%) belonging to aminoglycoside, B-lactamase, and sulphonamide families, respectively. Resistance to the penicillin and sulphamethoxazole drugs was found in 100% of isolates and was followed by resistance to tetracycline (73.5%), streptomycin (60%), trimethoprim sulphamethoxazole (56.5%), and kanamycin (53.5%). The phylogenetic groups A and B1 with the frequency of 65.8% and 30.6% considerably surrounded the majority of isolates, respectively. Conclusions: In Iran, diarrheic calves have an important role as the reservoir of resistant E. coli strains to some drugs which are registered for treatment of calf diarrhea.