The Effects of Acidity Upon the Growth of Pneumococcus in Culture Media Containing Proteins

Abstract

In a preceding communication (1) we have reviewed the accumulated evidence and presented additional data to indicate that a definite degree of acidity occurs in the lesions of pneumococcus infection. The r61e of the acidity in the lesions of pneumococcus infection is not as yet clearly understood. That acidity in vitro exerts a bacteriostatic effect upon the pneumococcus was proven by the studies of Demby and Avery (2), and Lord and Nye (3, 4), which showed that in broth, hydrogen ion concentrations greater than pH 6.80 not only inhibit growth but within a short time produce death of this bacterium. However, Morgan and Avery (5) have shown that the range of hydrogen ion concentrations at which pneumococcus growth can be initiated may be extended to a degree of acidity as great as pH 6.2 in broth by the addition of fresh unheated plant tissues. Possible evidence that acidity may be less active in inhibiting the growth of pneumococcus in animal tissue fluids is afforded by the observations of Felton and Dougherty (6) who were able to maintain growth of this microorganism in milk at pH 5.00, when adjusted with hydrochloric acid.The present paper is a report of studies on the effects of acidity upon the growth of the pneumococcus in culture media containing tissue fluids or animal proteins. Materials and MethodsCultures.--The findings reported were obtained with a standard strain of Type I Pneumococcus which was maintained at maximal virulence by mouse passage during the course of the experiments.Culture Media.--Beef infusion broth was prepared with neopeptone (Difco),