Treatment of clinical mastitis using antimicrobial susceptibility profiles for treatment decisions

Important considerations for antibiotic treatment of clinical bacterial mastitis are (1) using an antibiotic with an appropriate spectrum of activity; (2) selecting an antibiotic that attains and maintains an effective therapeutic concentration at the site of infection (milk, mammary tissue, or blood); (3) treating for an appropriate duration; and (4) avoiding adverse local or systemic effects and violative residues [1,2]. Antibiotics are often selected based on availability of labeled drugs, clinical signs in the cow, milk culture results for previous mastitis episodes in the herd, experience of treatment outcome in the herd, treatment cost, and withdrawal times for milk and slaughter [3-5]. There has been recent interest in optimizing treatment protocols to better target antibiotic administration, with substantial reliance on susceptibility testing of bacterial isolates from cows with clinical mastitis. The purpose of this review is to evaluate the role, if any, that antimicrobial susceptibility testing should play in guiding treatment of clinical mastitis.