Abstract
Background:
Diarrhea poses a major threat to calves herds, causing severe economic losses. Escherichia coli is one of the most important causes of diarrhea in animals, such as Enterotoxogenic E. coli (ETEC), Shiga toxin-producing E. coli (STEC), Enteropathogenic E. coli (EPEC), and Enterohemolytic E. coli (EHEC). Multidrug-resistant E. coli is emerging as a serious public health hazard.

Aim:
This study aimed to detect some virulence factors in Escherichia coli (sta, eae, stx1, stx2) and detect the antibiotic resistance rates of these bacterial strains.

Methods:
E. coli strains were isolated from 60 diarrheic calves on MacConkey and EMB agar, following Gram staining. Biochemical characterization for the subsequent steps was performed using the Hi25™ Enterobacteriaceae Identification Kit (KB003). Multiplex polymerase chain reaction was employed to detect virulence genes (sta, eae, stx1, stx2). Antimicrobial susceptibility testing was performed using the disk diffusion method.

Results:
E. coli was found in 53 of 60 diarrheic calves. Screening for virulence-associated genes revealed the following pathotype distribution: ETEC (carrying sta gene) 16.98%, EPEC (carrying eae gene) 13.21%, EHEC (carrying stx + eae genes) 13.21%, STEC (carrying stx1 and/or stx2 only) 32.07%, and hybrid strains (carrying mixed virulence genes from multiple pathotypes): 5.66%, while nonpathogenic strains (lacking all tested virulence genes) 18.87%. Regarding antimicrobial susceptibility testing, the study demonstrated high resistance to penicillin-G (92.5%) and amoxicillin (88.7%), while showing highest sensitivity to ceftiofur (82.1%) and ciprofloxacin (79.2%).

Conclusion:
The pathogenic E. coli strains represent one of the most significant causative agents of diarrhea in the calf. Furthermore, the Emergence of Multidrug-Resistant Bacterial Strains in Animals poses a potential threat to human public health.

Key words: Escherichia coli; Calves diarrhea; Virulence factors; Antibiotic resistance.