Isolation and Antimicrobial Sensitvity pattern of Salmonella species, Staphylococcus aureus and Escherichia coli from diarrheic dairy calves in selected dairy Farms of Mekelle and Wukro, Tigray, Northern Ethiopia.

A cross-sectional study was carried out from October, 2024 to February, 2025 in Mekelle and Wukro districts with the objective of isolation and determination of the antimicrobial susceptibility profile of Salmonella species, Staphylococcus aureus and Escherichia coli isolated from clinically diarrheic dairy calves. A total of 50 faecal samples were collected directly from the rectum of diarrheic calves and brought to the Microbiology laboratory of Mekelle University, College of Veterinary Medicine, for bacteriological examination. Isolation and identification of the microorganisms were done on the basis of their colony and cellular morphology, staining, and primary and secondary biochemical tests targeted for each pathogen. Furthermore, the antimicrobial susceptibility profile of the isolated bacteria were carried out using disc diffusion method. Only 38 of the total 50 faecal samples, yield Salmonella species, Staphylococcus aureus and Escherichia coli. Out of the total 38 fecal samples, 19 (50%) samples were positive for E. coli , 12 (31.6%) samples were positive for Salmonella species and 7 (18.4%) samples were positive for Staphylococcus aureus. The antibiogram study revealed that most of E.coli , Salmonella species and Staphylococcus aureus isolates were sensitive to Streptomycin, Polymyxin-B and Gentamycin. However, most of E.coli , Salmonella species and Staphylococcus aureus isolates were resistant to Clindamycin, Kanamycin and Methicillin. Most Staphylococcus aureus isolates were susceptible to penicillin, erthromycin and clindamycin whereas resistant was developed against penicillin, erthromycin and clindamycin by most isolates of E.coli and Salmonella species. In conclusion, E.coli and Salmonella were the bacterial species frequently isolated from diarrheic dairy calves in the study area. The results of this study indicated that the isolates were susceptible to limited antimicrobial agents. Most isolates were found susceptible to Streptomycin, Polymyxin-B and Gentamycin. Further characterization and potential effect of the isolated bacteria on the health and productivity of the calf needs to be studied further.