Abstract
In this study we aimed to detect diarrheagenic E.coli in buffalo calves with or without diarrhea, its virulence factors and antibiotic resistant pattern(s) as well as antibiotic resistance genes. Samples were collected from193 buffalo calves at different ages in El-Behera (110 and 83 samples from diarrheagenic and non-diarrheagenic calves, respectively). Ninety five (49.2%) E.coli positive samples were detected from calves with or without diarrhea by culturing and biochemical tests with higher incidence within the first 2 weeks of age. E.coli samples were subjected to antimicrobial disc diffusion susceptibility test by using 11 different antibiotic discs, which are the most commonly used in field treatment of calf diarrhea. High sensitivities (100%) to individual antibiotics as Amoxycillin and clavulonate, Lincospectin and Cefotaxime was detected while only two showed high resistances as oxytetracycline and Sulfamethoxazole trimethobrim with 91.6% and 50.5% resistance, respectively. PCR for identification of E.coli by detection of phoA gene revealed that 100% of the samples were E.coli positive. PCR for detection of E.coli virulence genes; eaeA and tsh as well as the antibiotic resistance genes; tetA(A) and Sul1 was performed. The eae(A), tsh, tetA(A) and Sul1 genes were found in 20%, 100%, 100% and 60% of E.coli samples, respectively. These results collectively indicate that buffalo calves can harbor enteropathogenic E.coli causing diarrhea at different ages. To our knowledge, this is the first report of detecting the tsh gene in E.coli isolated from diarrheagenic buffalo calves. This may raise concerns regarding the real distribution of tsh-positive E.coli in buffaloes, especially calves. Further, the tsh gene is mainly or exclusively detected in the Avian pathogenic E.coli (APEC) raising concerns on the role of buffaloes as a reservoir for pathogenic E.coli. Together, this can pose therapeutic challenge(s) to farm animals as well as zoonotic potential to contact human.

Key words: E.coli, Diarrhea, Buffalo calves, tsh gene, Egypt