Colony Variation in Pathogenic Strains of Bacterium coli Induced by the Use of Dyes

Abstract

There is perhaps no other single criterion for the identification of the culture type that is so significant as colony appearance. It is . regrettable, however, that in many investigations slight or no effort is made to proceed beyond recording the colony appearance. That this procedure is ill-advised is evident to every investigator who finds discrepancies in the characteristics of apparently established types.

In connection with studies on the pathogenicity of certain strains of Bacterium coli, note was made of the fact that some dyes tended to cause the appearance of clearly defined rough colonies with marked consistency in cultures that had been quite uniformly smooth for many generations. Use was made of a series of dyes to ascertain whether this was a constant phenomenon, perhaps associated with specific dye radicals, and there were found 4 of 25 common dyes which gave definite results.

Methylene blue (1-1000) yielded 60% roughs on the first transfer, with no satisfactory increase toward the desired 100% on repeated transfer. Crystal violet (Grübler, prewar stock) yielded 70-80% roughs on the first transfer with some tendency to increase on repeated transfer but falling short of 100%. Neutral acriflavine (1-1000) produced no roughs but practically 100% intermediates. Acriviolet, a mixture of crystal violet and neutral acriflavine, averaged about 95% roughs on the first inoculation, while the second, or at most the third transfer, even of thoroughly stabilized smooths, yielded 100% dissociation into rough colony types. The base used in these dye experiments was plain beef extract 3% agar, with no enrichment, hence there was no conflict between elements tending toward roughness and smoothness. A later report will deal with the restoration of roughs to smoothness, with a discussion of the effect of certain enriching substances favoring smoothness.