Comparative buffering value of American peptones

Abstract

Some time ago one of us 1 reported before this Society the results of the inquiry into the effect of the composition of the medium as affecting the reliability of the cultural methods of identification of bacteria, and has particularly insisted on the rôle of the buffer and on necessity of quantitative adjustment of media in respect to its buffer content.

In the present investigation we have attempted to determine the buffer content of a few of the commercial peptones with the view of determining the limits of possible variation in the buffer content in the media prepared in different laboratories as due to the choice of peptone alone. The method used was that of determining electrometrically the hydrogen ion concentration of the various peptone solutions before and after the addition to them of measured amounts of acid and alkali respectively. The study demonstrated the fact that initial reaction of different peptones varies within fairly broad limits, that due to complexity of composition the buffering action of any given peptone varies at different zones of hydrogen ion concentration, and that buffering action of one peptone at a given hydrogen ion concentration may exhibit as much as five times more buffering action than another peptone at the same hydrogen ion concentration. In general, the peptones tested showed the highest degree of variation in buffering effect in the zone of the hydrogen ion concentration limited between P_H = 9 and P_H = 8, and the lowest degree of variation in the zone between P_H = 4 and P_H = 5. As to the absolute concentration of buffering salts, these were found in most peptones to be the highest at the zone of the lowest concentration of the hydrogen ions and not in the zone of neutrality or of high hydrogen ion concentration where the buffering action would be most desirable for the use in media for identification of bacteria. Below is a table showing the relative buffering action of peptones at various P_H levels.