STAPHYLOCOCCI IN HEIFER MASTITIS BEFORE AND AFTER PARTURITION

Aseptic udder quarter secretion samples (n = 1112) from 200 mastitic a nd 65 non-mastitic control heifers from 160 different farms were colle cted for bacteriological examination and in vitro antimicrobial suscep tibility testing. Coagulase-negative staphylococci (CNS) were the most frequently isolated bacteria (57.8%). The percentage of Staphylococcu s aureus was 20.1, of streptococci 11.3 and of other pathogens 10.8. S taph. simulans, Staph. hyicus, Staph. xylosus and Staph. chromogenes w ere the most common CNS. Staph. simulans and Staph. hyicus were most f requently found in clinical samples after parturition, whereas other C NS were equally or more often found in control samples. Most CNS infec tions detected in the prepartum period were eliminated spontaneously o r with antibiotic treatment during early lactation, but the infected q uarters were more susceptible to new infection by other pathogens, Mil k N-acetyl-beta-glucosaminidase activities were measured to monitor ch anges in inflammation. Among the CNS infections, N-acetyl-beta-glucosa minidase activities mere highest for Staph. hyicus and lowest for Stap h. xylosus in the lactating mammary gland of heifers. CNS were resista nt to trimethoprim-sulphonamide, ampicillin and erythromycin. Staph. a ureus was more resistant than CNS to beta-lactamase-sensitive penicill ins.