Prevalence and antibiotic susceptibility of Staphylococcus aureus from lactating cows milk in Bahir Dar dairy farms

Staphylococcus aureus is competitive in milk and dairy environments; pathogenic strains have been found to cause disease in their host throughout the world. Therefore, this study was designed to assess the prevalence of Staphylococcus aureus and determine their antibiotic susceptibility from lactating cow milk. A cross-sectional study was conducted in Bahir Dar dairy farms from October 2012 to March 2013. A total of 218 raw milk samples from lactating cows were collected from dairy farms in Bahir Dar, North-West Ethiopia. The S. aureus bacteria were isolated on Mannitol Salt agar (Becton, Dickinson) where yellow colonies were selected and counted and then maintained for antibiotic susceptibility tests. Susceptibilities of the isolates were tested against 9 antibiotics using the Kirby-Bauer disc diffusion method. Overall, 98 milk samples (45%) were found to be contaminated with S. aureus with average count varying between 3.3×10² to 7.2×104 CFU/ mL. S. aureus prevalence showed significant variation among cows of different hygienic conditions (p < 0.05). S. aureus isolates were highly susceptible to ciprofloxacin (100%) followed by gentamycin (96%), chloramphenicol (74%), erythromycin (68%), trimethoprimsulfamethoxazole (66%) and tetracycline (60%). In contrast, isolates were highly resistant to penicillin (94%) and cephoxitin (62%). Most of the isolates (96%) were resistant to one or more antibiotics. In general, the results of the present study revealed that milk provided to the consumers in the city was found to be less hygienic. Thus, farmers should ensure strict personal hygiene and that of animals, and general sanitary condition of the farms should be improved and maintained.