In Vitro Activity of Antituberculous Agents in Relation to Ventilation in Culture Medium.

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In the previous paper, it was reported that tubercle bacilli inoculated onto the surface of Ogawa's glycerol egg medium were highly sensitive to the bactericidal activity of streptomycin and isoniazid contained therein. According to some report, however, such strong bactericidal activity is not exhibited against tubercle bacilli of submerged growth in Kirchner's liquid medium, where culture conditions are so different from those on Ogawa's glycerol egg slant. The present authors presumed that one of the factors responsible for such difference might be "ventilation" in test medium. And, this problem was examined using Ogawa glycerol egg slants of air-tight or air-passable conditions, and also using Kirchner's semi-solid agar mixed with the bacilli.<BR>In our laboratory, the cotton plug of Ogawa's slants inoculated with tubercle bacilli is usually replaced with a gum-cap in a week or so of incubation to prevent them from drying. This treatment does not allow the air ventilation on the surface of medium any more. However, as a device to prevent the medium from drying but to allow air-passage to some extent, a double-winded thread of 1 mm × 30 mm was passed through the center of gum-cap. Then, a streptomycin-sensitivity test was made of a strain of streptomycin-resistant tubercle bacilli comparing the growth between the case of air-tight slants and the case of air-passable slants. The results are shown in Table 1 and Fig.1, where stronger bactericidal and bacteriostatic activities are expressed in the air-passable condition than in the air-tight condition.<BR>In the Kirchner's agar-bac illi mixture, both the bactericidal and bacteriostatic activities of SM, INH and PAS were much stronger in the overlayer of the agar than in the bottom layer in which air ventilation was poor and oxygen tension was low. In the control case without antituberculous agents, numerous small colonies formed a turbid layer near the surface of the medium, but this colonial layer became sparse, increased in breadth, and moved deeper into the medium when the threshold concentrations of INH and SM were added. This finding also shows that the drug sensitivity of tubercle bacilli is lower in the poorly-ventilated area of the medium. In Ogawa's glycerol egg slants, colonial formations in both conditions were the same in numbers, but colonial size was larger in the airpassable tube indicating the rapid multiplication of tubercle bacilli. Therefore, it will be concluded that the activity of those antituberculous agents is stronger in the environment where air-ventilation is adequate for the bacilli and their multiplication is more rapid.
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In Vitro Activity of Antituberculous Agents in Relation to Ventilation in Culture Medium.

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