[In-vitro combined effect of antituberculosis drugs on Mycobacterium avium complex]

In-vitro combined activity of antituberculosis drugs on Mycobacterium avium complex strain 13034 (serotype 18) was observed. A twofold dilution series of each drug was combined with 17 additional drugs and the control without drug. Each medium was inoculated by a 0.02 ml-sample of four different bacterial suspensions, original suspension (10 mg wet weight per ml) and its 10(-5), 10(-6) and 10(-7) suspensions, and incubated at 37 degrees C for 28 days. The inoculation was made by a spiral loop that can deliver a 0.02 ml-sample by one inoculation. Since a total of media reached 6480 (1620 combinations x 4 different suspensions), only one strain was investigated in this study. Inoculation size used for determining minimal inhibitory concentrations was adjusted to 20 to 80 colony-forming units per medium. This was obtained by inoculating 10(-6) suspensions. The diameter of colonies was measured on media that were inoculated with 10(-7) suspensions. Since 96% confidence limits of determining minimal inhibitory concentrations are between 1/4 to fourfold, decrease or increase of the minimal inhibitory concentration equal to or above this level was regarded as significant. Such significant change of the minimal inhibitory concentrations occurred in combinations of drugs is shown in Table 2. As shown in tables, no antagonism was observed. The combinations, in which significant decrease was seen, contained ethambutol, sulfadimethoxine and ethionamide. It was shown that these concentrations of the drugs cause marked delay of growth. In control medium, the diameter of colonies was 5-6 mm, whereas in media containing one of these drugs, it was 1 mm.(ABSTRACT TRUNCATED AT 250 WORDS)