Wetting on Pathogenicity of Tubercle Bacillus 229 

 111 (2071) 



The effect of wetting on the pathogenicity and viability of 

 the tubercle bacillus- 



By W. P. LARSON and IRWIN A. MONTANK. 



[From the Department of Bacteriology, University of Minnesota, 

 Minneapolis, Minnesota.} 



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 dif- 

 fuse 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 depress- 

 ing 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 wet- 

 ting. 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 me- 

 dium 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 



1 Larson, W. P., Proc. Soc. Exp. Biol, and Med., 1921, xix, 62-63. 



2 Larson and Larson, Jour. Inf. Dis., 1922, xxxi, 407. 



