INFLUENCE OF pH OF MEDIA ON THE MINIMAL INHIBITORY CONCENTRATION OF CYCLOSERINE TO MYCOBACTERIUM TUBERCULOSIS
1965 Volume 40 Issue 6 Pages 213-218
Details
1965 Volume 40 Issue 6 Pages 213-218
It is said that Cycloserine (CS) is stable chemically in weak alkaline reaction, while Myc. tuberculosis grows well in acid media. These two matters seem to involve opposite factors in the resistance test of Myc. tuberculosis to CS. Accordingly, studies were made t investigate the influence of pH of media upon the minimal inhibitory concentration of CS to germ.
Media used were 1% Ogawa's egg slant and Kirchner's semi-liquid agar media. The basal media were adjusted to the pH level of 1.8, 3.2, 5.6, 6.6 and 7.0 with either HCl or NaOH, and the egg were added to them so that the pH level of condense water may become 5.6, 6.2, 6.8, 7.4 and 8.0. They incorporated with CS in the concentrations 0, 10, 20, 30, 50 and 100mcg/ml, respectively. The media were dispensed into test tubes 5ml each. Prior to use, Kirchner's semi-liquid agar media were kept in an incubator at 37°C for 24 hours to confirm sterility.
The following 5 strains were used for the studies: H37Rv, Aoyama-B, a strain isolated from sputum of a pulmonary tuberculosis patient never treated with CS previously and 2 strains from those treated with CS. From the 3 weeks old cultures of the primary isolation on 1% Ogawa's egg slant, emulsions were made in a concentration of approximately 1mg/ml employing electric photometer and were diluted 10 times, respectively. Then 0.1ml each of the emulsions was inoculated into media. Incubation period was 6 weeks at 37°C.
Results revealed that the most suitable pH level for the resistance test to CS was 6.8 in both kinds of media. The bacteriostatic effect of CS against Myc. tuberculosis seemed to be stronger in acid media than in alkaline ones. In both media, the minimal inhibitory concen tration of CS to the susceptible strain of Myc. tuberculosis was shown at the concentration of 20 to 30mcg/ml at a pH of 6.8.
