The optimum H-ion concentration for the growth of B. typhosus,and the effect of changes in H-ion concentration on the generation time

1. B. typhosus has a range of growth from P_H+5.0 — P_H+8.6, with an optimum growth at P_H+6.8 — P_H+7.0.

2. Stock cultures isolated from stools, blood, and urine have a more decided optimum than recently isolated cultures. In such cultures, the plateau is much more pronounced and extends over a wider range than in stock cultures. The latter is suggestive of microbic adaptation to changes in H-ion concentration in body fluids, particularly urine and bile.

3. The growth curve is influenced by changes in H-ion concentration.

At P_H+7.0, the minimum generation time at 36.0° C. — 37.0° C., is 31 minutes. Maximum growth begins on the average after five hours incubation.

At P_H+7.8, the minimum generation time is 33.4 minutes. The maximum rate of growth is reached by the eighth or ninth hour.

At P_H+5.4 the minimum generation time is 41.3 minutes. The maximum rate of growth is reached after 9¾ hours.