The Effect of pH at Different Temperatures on the Growth of Bacterium coli with a Constant Food Supply

SUMMARY: The effect of pH over the range 5–9 on the growth of Bacterium coli with a constant food supply was studied at 20 and 30°. Total and viable counts were made and growth curves constructed. To discover the effects of starvation, sampling was continued after stopping the food supply.

The total count always substantially exceeded the viable. Each growth curve showed an ‘initial phase’ of varying daily increment in cell numbers merging into a ‘steady phase’ of roughly constant increment, which continued as long as food was supplied. Low pH slightly shortened the initial phase, low temperature greatly prolonged it. In the early initial phase development was slow at pH 5, but later became exceedingly rapid. Altogether, the conversion of the food supplied into (total) bacterial cells was best effected in conditions of low temperature and low pH, low temperature being the more important. These conditions also favoured high viable counts, and consequently smaller non-viability indices.

During starvation the apparent total counts declined, except at 30° and pH 5, when a steady increase occurred. Higher pH and lower temperature led to faster rates of decline. Viable counts remained approximately constant at pH 5, but otherwise the numbers declined.