Abstract
The optimal growth pH and conditions necessary to give a full manifestation of the effect of reductants upon the growth of Campylobacter fetus were investigated using static cultivation. The multiplication of cells was limited to a narrow range of added reductants. Thioglycollate supplemented without heating produced heavy growth in combinations of 0.05% at pH 6.80 or 0.1% at pH 6.60, and 0.2% at pH 7.00 or 7.20. Although the stimulating effect depended upon the time between the addition of the supplement and inoculation, two prominent peaks in the growth curve always appeared with both alkaline and acidic pH ranges of the medium. Autoclaving the medium with some SH compounds brought about this growth only at around pH 6.50. Consequently there was a uniform decrease in the initial pH. L-Cysteine and ascorbic acid also gave similar effects. Glucose remarkably prevented the growth promotion due to SH compounds. Optimal initial reduction potential for growth in a semisolid medium was considered to be -0.05 to -0.08 volt at an initial pH of 6.60. SH compounds supplemented without heating brought about a marked longevity of the culture in comparison with a culture in an autoclaved medium of the same composition. For the growth of C. fetus in semisolid medium, it was important to avoid decreasing the growth-promoting activity of some of the supplemented SH compounds by not heating but adding the supplement aseptically. Also a rigid regulation of the pH, the concentration of the added reductants, and the time of inoculation into the fresh medium were important.
