[Sensitivity of mastitis pathogens to antibiotics and chemotherapeutic agents]

Sensitivity of mastitis bacteria to antibiotics and chemotherapeutic agents. The author tested the following bacteria, isolated from milk: -2236 strains of streptococci (1384 of group B, 262 of group C, 62 of group D, 109 of E, 16 of F, 24 of G, 7 of H, 11 of K, 270 of L, 5 of M, 41 of N, 45 of P); 361 ungroupable streptococci; 18,481 CAMP-positve, 1,966 CAMP-negative beta-haemolytic streptococci; 5,403 CAMP-negative, non-haemolytic streptococci; 1,179 strains of staphylococci, 596 of coliforms, 477 Corynebacterium pyogenes. They were tested against penicillin, streptomycin, chloramphenicol, oxytetracycline, and some were also tested against Nifuzin, Suprazid and sulfadimidine. A high proportion of the streptococci, which were the dominant mastitis agents, was sensitive to penicillin: - 97.2% of group B, 99.2% of C, 96.3% of E, 99.6% of L, 98.7% of CAMP-positive strains, 99.6% of beta-haemolytic strains. Only 20 strains of streptococci (0.08%) were resistent to penicillin. More than half were resistent to streptomycin (52.19%) while 44.38% showed decreased sensitivity. Nearly all streptococci (98.53%) were susceptible to chloramphenicol. With oxytetracycline most CAMP-positive (96.4%) and group B streptococci (95.4%) were sensitive, but only 53.4% of groups C, G and L and 31.4% of beta-haemolytic streptococci were. Sensitivity to Nifuzin, Suprazid and sulfadimidine was variable: the proportion of streptococci sensitive to each drug was 75.32%, 58.51% and 66.05%. During the ten year period of testing (1963 to 1972) the only evidence of an increase in resistance was with oxytetracycline, involving streptococci of groups N and P, the ungroupable strains and above all the beta-haemolytic strains. 82% of the staphylococci were sensitive to penicillin, 89.6% to streptomycin, 95.5% to chloramphenicol and 96.2% to oxytetracycline. Between 1963/66 and 1972 the proportion of strains showing reduced sensitivity to penicillin rose by 28.1%. With sulphonamides, 80.4% were sensitive to Suprazid and 80.6% to sulfadimidine, showing that these drugs were less effective in vitro than antibiotics. 92% of staphylococcal strains were sensitive to Nifuzin. Among coliform bacteria the dominant pattern was sensitivity to streptomycin (96%-, chloramphenicol (97.3%), oxytetracycline (88%), Nifuzin (95%), Suprazid (92%) and sulfadimidine (91.3%). The only change between 1963 and 1972 was a 14% increase in strains resistant to oxytetracacline. Strains of Corynebacterium pyogenes were generally sensitive to penicillin (100%), chloramphenicol (100%) and oxytetracycline (99%); the proportion sensitive to streptomycin was 88%, to Nifuzin 84.8%, and to sulfadimidine only 36%. There was no change in the sensitivity pattern between 1963 and 1972.