Dissociation of microbic species. IV. Factors influencing the acid agglutination optimum of types D and G

Abstract

It is generally supposed that the acid flocculation optimum of bacteria is referable only to the C_H+ and is not influenced by the character of the buffer salts or the anion of the acid. This interpretation is questionable in the light of the following facts. Microbes D and G were tested against a glycocol-HCl buffer series, range P_H = 3.0 to P_H = 1.2. The same suspensions were tested simultaneously with the Na lactate-lactic acid and the Na acetate-acetic acid series employed in the experiments described in the preceding paper. The results are presented in the following table.

This experiment indicates that other factors besides the C_H+ are important in the interpretation of the acid agglutination point of the organisms in question. For example, complete flocculation of type G occurs at P_H = 3.0 in the glycocol HCl series, while no flocculation whatever was observed at the same P_H in the Na lactate-lactic acid series. It would appear that either the Cl⁻ of the acid, or the glycocol possessed the property of broadening the optimum zone or of shifting it toward a higher P_H+.

This and other considerations led to experiments which suggest an explanation for the granular growth of microbe G in plain broth. Washed suspensions of this organism are strongly agglutinated by beef infusion between P_H = 7.4 and 6.8. This range represents the C_H+ occurring during the growth of type G in broth. On the other hand, peptone (Fairchild) and Na₂HPO₄, the other constituents of broth, agglutinate type G very little or not at all in this acidity.

Types G and D were next subjected to tests with varying amounts of beef infusion, which were adjusted to varying acidities, from P_H = 7.5 to P_H = 2.0.