Effect of Silica on the Growth of the Tubercle Bacillus.

Abstract

In silicosis, silica in some form or in some way seems to increase the pathogenic effects of the tubercle bacillus. It therefore suggested itself that silica might have a stimulating effect on the growth of the tubercle bacillus in vitro. Accordingly, I carried out a number of cultural experiments, by adding 1 cc. of sodium silicate or silicic acid, each standardized to contain 1 mg. of the silica used in the preparation per cubic centimeter, to every 100 cc. of Dorset's egg medium, modified by replacing the distilled water by a beef infusion free from added peptone, or sodium chloride, and adjusted to a pH of 7.6. The results obtained in these preliminary studies have been consistently uniform, and indicated a definite stimulating effect of the added substances, even though the estimated quantity of silica is 0.001 mg. per cc. of medium. This is shown by a lessening of the latent period, and a greater luxuriance of growth. The stimulating effect appeared to be continuous throughout the period of growth. I was thus able to produce readily visible colonies in initial cultures from guinea pigs, and directly from human sources, such as pus, urine and ascitic fluid, in a much shorter time than with other media. In one instance, a primary culture was isolated from ascitic fluid on sodium silicate medium, whereas we failed to obtain any growth on the control tubes of our Dorset's egg medium, with or without glycerine. Colonies became visible in about 6 days, growth continued rapidly, and could be considered luxuriant within 3 weeks. These observations now cover 20 primary cultures, 17 of which were isolated through guinea pig inoculation, and the remaining 3 directly from human materials.