Resistance of coagulase-negative staphylococci isolated from sheep to various antimicrobial agents.

Staphylococcal resistance to a variety of antimicrobial agents, defined as inhibition of bacteria growth in the presence of an antimicrobial agent, was approximately 75 per cent among coagulase-negative staphylococci isolated from milk and the teat skin of sheep. Resistance to broad spectrum antibiotics such as chloramphenicol and tetracycline as well as resistance to the combination of trimethoprim/sulphamethoxazole commonly used for the treatment of animals, was high in both groups of isolates. Four isolates of Staphylococcus epidermidis and three Staph xylosus isolated from the milk of dairy ewes were resistant to methicillin. Methicillin resistance is prevalent among human staphylococcal isolates and resistance to this antibiotic may reflect human handling of sheep.