Sulfamethoxazole, Trimethoprim, および両者配合の抗菌力測定法の検討と, 患者分離株の感受性

抄録

Influence of various components of a medium on activities of sulfamethoxazole (SMX) and trimethoprim (TMP) against Escherichia coli NIHJ JC-2 strain was investigated. Yeast extract or p-aminobenzoic acid added to M9 minimum liquid medium competitively antagonized the antibacterial activity of SMX, while lactoalbumin hydrolysate or methionine, glycine, adenine and thymine added to the medium non-competitively antagonized both SMX and TMP. Folic acid and N^{5, 10}-methenyl tetrahydrofolic acid were found to have no antagonizing effect on the activities of both drugs against Escherichia coli.
The replica method was found to be inadequate for assaying antimicrobial activities of SMX-TMP due to the difficulty in controlling inoculum size. Reproducible sensitivity tests were possible by employing a plate dilution method with MUELLER-HINTON agar supplemented with 7.5 % hemolyzed horse blood. Sensitivity levels of some bacterial strains as assessed by this method were found to be significantly higher than those employing a tube dilution method with a minimum liquid medium and a small inoculum size.
A marked potentiation of antimicrobial activity was demonstrated by SMX-TMP combination on drug-sensitive Escherichia coli M48-34 (pab), a sulfonamide-resistant substrain, M48-34 (sul, met, gyl) and a R⁺substrain, M48-34/R 100 (fi⁺, sul, str, tet, cml). The amount of SMX necessary for potentiation, however, was much higher with M48-34/R 100 strain than with the parent strain. Siginificant potentiation was confirmed by the combination on gram-positive bacteria regardless of their sulfonamide sensitivities.