The action of dilute acids upon bacterial growth in optimum hydrogenion concentration.

Abstract

THE use of culture metlia of definite PiI concentration has suggested enquiries into the limiting and optimum zones for each bacterium. So far as the initial reaction of tlie medium is concerned, tliis has been a simple matter. But when it becomes necessary to determine the firial reaction of the niediani, to consider the composition of varying media, arid to allow for intervening conditions which favour or hinder growths, the probleni presents niany new aspects. Not the least among these, is the appearance of certain acids or salts as a direct result of the ruetabolisni of the inseminated organisms. In order to study the effects of these substances, it was thought worth while, therefore, to add minute quantities of different acids to certain media, so as to observe the early rate of growth of bacteria, under conditions which usually obtain oiily a t a later stage. To this end, an optirriuiri P, Concentration was determined for each strain in the presence of added acids. That such a series of observations would yield b a t crude firidirigs was fully appreciated: yet i t seemed possible that some of the unknown, and at present uncontrolled factors might be more clearly defined and openings he found for additional enquiry. After due consideration of the mass of work upon the phase of lag, etc., and an extended experience with the iiieasurerrient of growth by "opacity" methods, it was decided to approach the subject from the standpoint of total, or hourly, generations at the first maxinial period of growth. The Initial Reaction of IVediam and the Maximum Gvowth. Prior to the determination of the behaviour of bacteria under the conditions just laid down, it was evident that a preliminary survey should be made of the growth from the standpoint of the initial reaction of the culture medium. The expenses have been met by grants from the Medical Research Council, and the University of Bristol Colston Research Society. \Ye desire to acknowledge the painstaking and careful assistance rendered by X r F. Nichols.

Behaviour of Diphtheria Bacilli in Acidified Media, especially with reference to Virulence Tests

“…Bunker (1919) found the acid limit to be pH 5-7 in fermented veal broth, but states that when growth is started above this point, the acidity may be increased without harm to the bacteria. Dernby (1921) obtained growth in unfermented buffered veal broth at pH 6-0, and Walker Hall and Fraser (1922) record the same figure in casein digest.…”

“…They point out that a substance devoid of vitamine, namely charcoal, has quite an appreciable growth-promoting effect. Walker Hall and Fraser (1922) 14 6-8 6-6 6-4 6-0 56 5-4 6-8 6-6 7-5 8-0 8-2 74 7-0 7-0 6-0 5-9 5-6 7-0 7-6 8-0 8-6 93 8-1 77 75 74 7-0 6-0 8-0 8-1 8-4 8-6 9-0 6-8 6-6 6-4 7-0 7-2 7-5 6-8 6-5 7-3 8-0 8-3 7-5 7-2 7-1 7-0 7-4 7-6 7-4 7-6 7-8 8-0 8-1 8-1 7-7 7-6 7-6 79 8-2 8-1 7-9 8-5 9-0 9-0 6-8 6-7 7-6 7-9 8-1 8-3 6-8 8-2 9-0 9-0 9-3 7-5 6-9 7-8 8-2 8-2 8-3 7-4 8-0 8-8 9-0 9-3 6-8 6-8 6-9 7-0 7-3 7-6 6-8 7-1 7-5 7-6 7-8 7-6 7-6 7-6 7-8 8-2 8-3 7-4 8-3 8-4 8-8 9-2…”

“…Walker Hall and Fraser (1922) pointed out the selective action of various acids for the acceleration or retardation of the lag phase in bacterial growth. Davis and Perry (1916) investigated the action of individual amino-acids and other substances on the growth of toxic strains of diphtheria bacilli.…”