Abstract

Staphylococcus aureus is a major problem of public health which causes a number of human and animal diseases. In order to isolate and identify S. aureus from milk of dairy cows and nasal swabs of farm workers of different farm settings, a cross sectional study was conducted on a total of 260 lactating dairy cows milk and 68 nasal swabs of farm workers in selected dairy farms around Addis Ababa, Ethiopia. The collected nasal swabs and milk (California Mastitis Test Screened) were cultured on sheep blood agar.Presumptive Staphylococci colonies were sub-cultured on mannitol salt agar andconfirmed by BiOLOG Identification system. Antimicrobial susceptibility pattern of S. aureus isolates was done by Kirby-Bauer disk diffusion method using twelve antimicrobials. The prevalence of S. aureus was found to be 51 (15.5%) out of the total samples examined. In addition, the prevalence of S. aureus was 42 (16.2%) from milk of 260 lactating dairy cows and 9 (13.2%) from nasal swabs of 68 farm workers. The prevalence of S. aureus ranges from 8 (8.9%) to 13 (36.1%) in selected dairy farms where poorly managed farms showed high prevalence. S. aureus was more likely to occur in cows that were poorly managed and treated frequently with antimicrobials. Antimicrobial susceptibility test revealed the resistance of S. aureus to the tested antimicrobials. Thus,out of a total of 51 isolates, high resistance rate was observed primarily to penicillin G 47 (92.2%) followed by tetracycline 34 (66.7%), amoxicillin-clavulinic acid 19 (37.3%), oxacillin 17 (33.3%), cephalothin 14 (27.5%) and low level of resistance to chloroamphenicol 12 (23.5%), erythromycin 12 (23.5%), sulphamethoxazole-trimethoprim 11 (21.6%), gentamicin 10 (19.6%), clindamycin 9 (17.6%), vancomycin 2 (3.9%) and rifampicin 1 (2%). There was no statistically significant difference (p>0.05) between type of samples in determining resistance pattern to each antimicrobial except for pencillin G and tetracycline. Multidrug resistance was also observed in 23 (45.1%) of the total isolates and most of them were from milk samples, 20 (47.6%) with no statistically significant difference (P>0.05) between dairy farm workers and dairy cows. S. aureus becamealmost resistant to β-lactams and tetracycline. Hence, antimicrobial susceptibility should be conducted before treating dairy cows. Consequently, reduction in transfer of resistant S. aureus strains between humans and animals could possibly be made.

Key words: Staphylococcus aureus, dairy cow milk, farm workers, antimicrobial susceptibility test, Ethiopia.