Direct silver staining of spirochetes and flagellated bacteria

Abstract

The discussion of the nature of the structure now called spirochete (Treponema) pallida — whether a microorganism or some histological elements — led me to try to effect the silver staining directly upon smear preparations prepared from serum exudates obtained from syphilitic lesions. While engaged unsuccessfully in this endeavor, Stern 1 of Prag published a simple method for staining the spirochetes directly with silver nitrate. When the deposit of silver presents a metallic sheen, the impregnation is regarded as sufficient. I have found the method very simple and sufficient; but I have obtained better results from long (3-4 days) than from short (1-2 days) exposures. The length of exposure required will depend somewhat upon the weather (strength of light) and the thickness of the spread. Moderately heavy spreads have given me better results than thinner ones, and impression preparations better than smear preparations. In the shorter exposures, some of the spirals will show uniform breaks between the curves which may be attributed to the relation existing between spirochete and medium, the more superficial curves being first impregnated. By longer exposure, the broken spirals are made complete, probably by impregnation of the deeper-lying curves. Disagreeable precipitation is not present on the serum-covered film, but occurs on the adjacent uncovered glass. The direct demonstration of silvered spirochetes may be taken as a concluding proof of the microorganismal nature of the spirals.

Other spirochetal organisms, from the buccal cavity, etc., may be silvered by this method, and bacteria may also be silvered. In a few comparative tests which I made, the degree of impregnation was greatest with the pallida. Whether this is to be accounted for by elective affinity or difference of medium in which the organisms were embedded I cannot say.