抄録
Investigations were performed on the effect of peptidic antibiotics such as thiopeptin and bicyclomycin on ureolysis in rat. Neither drug inhibited urease activity of ileumcaecum contents. Thiopeptin (46 mg/kg/d) or bicyclomycin (100 mg/kg/d) was orally administered to rats two days before the measurement of 14C-ureolysis : the percentage of recovery of radioactivity expired into the breathing air was assayed (in vivo measurement). The depression percentages with thiopeptin and bicyclomycin were 59 and 35%, respectively. Urease activities of ileum-caecum contents of rats (in vitro measurement) 4 days after the treatment with thiopeptin and bicyclomycin decreased to 7 and 60% of the control rats, respectively. When being fed with thiofeed containing 100 ppm thiopeptin (10 mg thiopeptin/kg/d) for ten days, urease activity (in vitro measurement) decreased to 50-65%, but feeding of bicyclofeed containing 1000 ppm bicyclomycin (100 mg bicyclomycin/kg/d) was not effective. Susceptibility of 24 strains of intestinal bacteria to these antibiotics was examined. Thiopeptin inhibited strongly the growth of Eubacterium lentum and Eubacterium aerofaciens (MIC were 23 and 26.6 ng/ml, respectively), which were known to be urease-producing bacteria. The growth of other ureasenegative bacteria was also inhibited by thiopeptin in the similar concentrations. These results suggested that the intestinal flora were markedly affected by the antibiotics, resulting in the depression of ureolysis in vivo and decrease of urease activity of ileumcaecum contents. Bicyclomycin did not affect the growth of test bacteria at all.
