THE INFLUENCE UPON BACTERIAL VIABILITY OF VARIOUS ANIONS IN COMBINATION WITH SODIUM

Abstract

Reasonably uniform and significant results may be obtained by study of the viability of Escherichia coli in a simple synthetic medium (Dolloff''s) in presence of various electrolytes. Previous washing of the cells used for inoculation increases their sensitiveness to electrolytes. All electrolytes studied (NaOH, NaHCO3, Na2CO3, Na2SO4, Na2HPO4, NaH2PO4, Na3PO4 and mixtures of all of these salts with NaOH) exhibit the same general qualitative effect. All stimulate bacterial growth in low and inhibit it in higher concentration. The stimulating effects in low concentration appear to be a direct function of the Na content,[long dash]a Na concentration of 0.001-0.020 molal strength being most favorable unless other factors supervene. The inhibiting effect of higher concentrations of electrolytes is due to 2 factors[long dash]Na concentration and pH. These 2 factors appear to explain most of the observed phenomena. Maximum stimulation occurs with a Na concentration of 0.10m and a pH of about 7.5. Decrease of Na concentration and decrease of pH below this optimum results in a gradual decrease of stimulating effect. Increase in Na or pH causes a much more rapid change from stimulation to inhibition. Na concentrations above 0.60 m and pH values above 8.3 are inhibitive and cause a decrease instead of an increase in bacterial numbers, as compared with the salt-free control. If Na concentration and pH value be within a favorable range, the presence of the phosphate radicle exerts a distinctly stimulating influence. It is suggested in view of these facts that 2 major factors govern bacterial viability under the conditions of these experiments. The 1st is the cation concentration, and according to the theory of Winslow and Dolloff (1928) the effect of all cations is qualitatively alike and differs only in degree. The 2nd factor is the pH, which, with a similar cation, is determined by the anion. The phosphate radical has a specific stimulating effect of its own if cation concentration and pH be optimum. It is suggested that in studies of salt action on bacteria (and perhaps other organisms), the attempt should be made to explain observed results on such simple bases as those outlined. Assumptions of "specific salt action" and of "antagonism" and of the influence of one salt or alkali or acid on the toxicity of another need not be made, except where this simpler explanation fails.