ANTIBACTERIAL ACTIVITY OF TILMICOSIN AGAINST PASTEURELLA-MULTOCIDA AND ACTINOBACILLUS-PLEUROPNEUMONIAE ISOLATED FROM PNEUMONIC LESIONS IN SWINE

Sixty one strains of Pasteurella multocida and 35 strains of Actinobac illus pleuropneumoniae isolated from pneumonic lesions of porcine lung s during the period from 1985 to 1989 in Japan were tested for antibio tic susceptibility to chlortetracycline (CTC), thiamphenicol (TP), tyl osin (TS), acetylisovaleryl-tylosin (AIV-TS), tilmicosin (TMS), micros amycin (MRM). Most strains of both species were sensitive to CTC, TP a nd TMS. Growth of fifty-one strains (83.6%) and forty-six strains (75. 4%) of P. multocida were inhibited with 3.13 mug/ml of CTC and 0.78 mu g/ml of TP, respectively. TS showed low activity against almost all st rains (MIC greater-than-or-equal-to 6.25 mug/ml). Fifty-eight (95.1%), twenty-three (37.7%) and fifty (82%) of P. multocida showed MICs of g reater-than-or-equal-to 6.25 mug/ml against AIV-TS, TMS and MRM, respe ctively. The MICs of A. pleuropneumoniae against CTC were less than 1. 56 mug/ml. Thirty-two strains (91.4%) and 33 strains (94.3%) of A. ple uropneumoniae were inhibited with 3.13 mug/ml of TP and TMS respective ly. However, TS, AIV-TS and MRM showed low activity against all of A. pleuropneumoniae (MIC greater-than-or-equal-to 6.25 mug/ml). Three dif ferent resistance patterns were observed in P. multocida and two in A. pleuropneumoniae isolates, respectively.