“The gradual decrease in bacteria of the production of agglutinable substance”

At the last meeting of the Society of American Pathologists and Bacteriologists an informal statement of this fact was made by Dr. Welch for Drs. Marshall and Knox. The experiments of Dr. Collins and the author are reported here because they were undertaken in a slightly different way and also because a certain number of confirmatory observations are of value.

The maltose-fermenting paradysentery bacillus of Flexner was grown for twenty-four hours on each of eleven consecutive days in fresh bouillon solutions of the serum from a horse immunized through oft-repeated injections of the bacillus. The serum strength in the solutions used was 1.5%, 4% and 15%. The serum agglutinated the culture before its growth in the solutions in dilutions up to 1 in 800, and was strongly bactericidal in animals. After eleven transfers the culture grown in the 15% solution ceased to be distinctly agglutinated by the serum in any dilution and ceased to absorb from the serum any appreciable amount of the agglutinins acting upon the original culture. The cultures grown in the 1.5% and 4% solutions were changed to a less degree and agglutinated in dilutions up to 1 in 100 and 1 in 60 respectively, and continued to absorb agglutinins. The recovery of the capacity to be agglutinated was very slow in the culture grown in the strongest serum solution, when it was from time to time transplanted in fresh nutrient agar. The other cultures recovered this characteristic more rapidly.

The first culture, after growth for sixteen weeks, during which it was transplanted forty-three times, agglutinated in dilutions up to I in ZOO, and after twenty weeks in dilutions up to I in 400. The culture grown in 4% solution of serum agglutinated after sixteen weeks in dilutions up to I in 500, and one in 1.5% agglutinated in dilutions up to I in 800. This diminution and final almost complete lack of development of agglutinable substance in bacteria grown in a serum rich in agglutinin and immune bodies is interesting. It showed not only a rapid variation in bacteria of essential characteristics, but also indicated a possible means of adapting themselves to resist destruction in the living body, since the bacteria which ceased to produce agglutinable substance and probably, also, less substance with affinity for other antibodies, might be considered less vulnerable to these substances.