Studies in bacterial Variability. The Experimental Production of a Mucoid form of B. paratyphosus B

Abstract

IN the course of experiments which led to the appearance of what I have termed "dys-agglutinable" forms of certain. bacteria (Walker, 1922), several non-motile (or only very feebly motile) dys-agglutinable strains of B. paratyphosus B were produced at different times. They were all derived from an ordinary "eu-agglutinable" laboratory strain of the bacillus by the method, described by me on previous occasions, of repeated subculture in media containing a proportion of specific agglutinating serum. One of these derived strains presented, in addition to its non-motility and dys-agglutinability, other novel characters of interest, particularly in regard to its growth on the surface of agar. On that medium the appearance of colonies was such as to suggest that the term Mucosus would be appropriate to describe the growth obtained. It at once recalled the description given by W. Fletcher (1920) of a mucoid form of B. paratyphosus B obtained by him in two cases from the stools of chronic "'carriers."The original culture from which my mucoid strain was eventually obtained had been an ordinary laboratory strain of B. paratyphosus B, in use in the Standards Department, and had shown on plating a mixture of the two common types of colonies described by Arkwright (1921) as "rough" and "smooth."The dys-agglutinable strain derived from this paratyphoid bacillus by the method already mentioned was obtained in the following manner. A plating on agar, made from the eighth successive subculture in agglutinating serum diluted 1 to 4 with ordinary bouillon, at the end of four weeks from the commencement of this particular experiment, showed two very different types of colony after 24 hours' growth. The one was thin with bluish translucency, and presented the appearance of ordinary paratyphoid colonies. In hangingdrop its bacilli were actively motile. The other was thick, opaque, round, umbilicated, yellowish, somewhat waxy and moist looking, and its bacilli were almost, if not entirely, non-motile when examined microscopically.One of the thick colonies was subcultivated in diluted agglutinating serum (1 to 4), and after 48 hours' incubation it was plated out on agar. The plating