Abstract
In papers published from this laboratory during the past three years attention has been directed to changes produced in cultures of pellicle forming bacteria by adding surface tension depressants to the media. The changed form of growth from pellicle to diffuse growth thus induced has been attributed 1 to differences in degree of wetting of the bacteria.
We have found that the tubercle bacillus can be made to grow beneath the surface of glycerine broth by appropriately depressing the surface tension of the medium. The tubercle bacillus, like other pellicle forming organisms, we believe, grows on the surface because of its high fat content which tends to resist wetting. In a recent paper Larson and Larson 2 have shown that practically all aerobic bacteria may be grown on the surface of broth by growing them on media from which they may store up fat in increased amounts.
The present study concerns the effect of wetting on the viability and pathogenicity of the tubercle bacillus. A virulent culture of this organism was grown in glycerine broth to which had been added sufficient soap to depress the surface tension to 44 dynes.
Growth under these conditions is under the surface of the medium and is slower than when grown under the usual conditions. Inoculation of such cultures subcutaneously into the flank of guinea pigs was followed by a slight enlargement of the inguinal glands of the side inoculated. Within the following ten days this glandular enlargement had receded, after which the animals showed no signs of tubercular infection.
The mechanism of this rapid loss of pathogenicity is difficult of analysis at the present time. However, if the hypothesis is accepted that pellicle formation of the tubercle bacillus is an indication of minimum wetting, the same arguments may be used to explain altered pathogenicity.
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