Abstract
Yersinia enterocolitica is a bacterial pathogenic organism which distributed widely in several countries including Iraq, among a broad range of environmental and animal reservoirs as cows. This study was conducted to isolation and biochemical examination of Y. enterocolitica isolated from diarrheic cows, antibiotic sensitivity and molecular testing of study strains to indicate existence of virulence genes. Initially, fecal samples were collected from 87 diarrheic cows, inoculated in Nutrient broth, and the colonies were re-inoculated on MacConkey and Blood agars. Then, suspected Y. enterocolitica strains were tested molecularly by PCR through targeting 16S rRNA gene, and four virulence genes (hreP, fes, fepD, and sat). Additionally, antibiotic sensitivity testing for study strains was done on Muller Hinton agar. Traditionally, Y. enterocolitica were isolated from 16.09% diarrheic cows, which biochemically shown a negative reactivity to Gram staining, motility, Esculin hydrolysis, oxidase, indole, and citrate; but a positive activity to catalase, methyl red, motility test at 25°C, urease, arabinose fermentation, and Voges-Proskauer. The antibiotic sensitivity testing revealed a significant higher sensitivity to Ciprofloxacin, Gentamicin, Streptomycin, Sulfamethoxazole / Trimethoprim, and Ceftriaxone; while, resistance was seen to Amoxicillin, Tetracycline and Amoxicillin / Clavulanic acid. Targeting 16S rRNA gene, molecular PCR assays revealed that all study Y. enterocolitica strains were positive; whereas, investigation of virulence genes has detected a significant increase in fes (85.71%) and hreP (85.71%) genes; while significant decreases were seen in existence of sat gene (71.43%) when compared to fepD gene (78.57%). In conclusion, Y. enterocolitica is a notable enteric pathogen in diarrheic cows with a high prevalence of virulence-associated genes, particularly fes and hreP, highlights the pathogenic potential of these strains, and it possible roles in increasing of pathogenicity and reducing of antibiotic sensitivity

Key words: Antibiotic sensitivity test, Biochemical profile, Iraq, Phylogenetic analysis, Sequencing data