Occurrence of Coagulase-negative Staphylococcal mastitis in dairy cows

Abstract Objective: To study the prevalence of Coagulase-negative Staphylococci in clinical and subclinical mastitis in dairy cows. Design: Case-control study. Animals: 415 lactating Holstein cows. Procedures: A total of 896 quarter milk samples were collected aseptically from 415 dairy cows for bacteriological examination (mastitic cows, n=50; healthy cows, n=174). Identification of different bacterial isolates followed by antibiotic sensitivity test for Coagulase-negative Staphylococci (CNS) was carried out, using disc-diffusion method against 13 different antibiotics. Results: 224 out of 415 cows (54%) were proven to be mastitic (12% clinical mastitis, 42 % subclinical mastitis). Coagulase-negative Staphylococci were the prevalent isolate (32%). CNS was recorded in 25.7 % of clinical cases and 34% of subclinical mastitis. The antibiogram of CNS isolates against 13 different antibiotics revealed high level of resistance to ampicillin (85%) and oxacillin (85%). However, they were less resistant to vancomycin (5%). The other antibiotics showed variable levels of resistance ranging from 40-75%. Conclusion and clinical relevance: Coagulase-negative Staphylococci were the most common bacteria isolated from mastitic cases. Multi-drug resistance was observed among CNS with high resistance to ampicillin and penicillin, so the use of such B-lactam antibiotics should be restricted specially if there were suspected cases of Coagulase-negative Staphylococci