Motility in the Examination for B. Typhosus and Related Pathogens

Abstract

Bacteriologic diagnosis of typhoid fever and related infections has centered about the utilization of biochemical differences between the pathogenic organisms concerned and the non-pathogenic forms associated with them. The usual initial procedure in the examination of a suspected typhoid stool is seeding upon some lactose plating medium to eliminate all but the non-fermenting organisms present. The principal reasons to explain the failure to isolate the typhoid bacillus are: scarcity of B. typhosus in the stool, or the overwhelming antagonistic action of the associated bacteria. Glycerin, bile, and selectively bacteriostatic substances such as brilliant-green have been incorporated into the stool fluid or into the media. The object is either to forestall the destruction of whatever typhoid bacilli may be present or to hinder the growth of the non-pathogenic organisms of the mixture without inhibiting B. typhosus.

Given a mixture in which the desired bacteria were present in very small numbers, it would seem, a priori, that instead of inhibitive methods, enrichment would be the procedure of choice. Based upon the conception that, under similar conditions, B. typhosus and the Salmonella organisms are more actively motile than B. coli, the principal interfering organism, we have experimented with methods of selective enrichment. 1

Our first attempts with liquid media were only partially successful. Difficulties with diffusion and convection currents during incubation were such as to make the results very irregular. The next trials were with semi-fluid agar in test-tubes; the inoculum was introduced into the bottom of the column of soft agar by a capillary pipette. Disruption of the agar by the pipette allowed rapid ascent of all the organisms in the test mixtures or in feces. Our best results have been with small U-tubes containing ordinary beef infusion to which 0.2% agar has heen added.