Abstract
It seems from a review of the literature bearing on the question of the rôle of vitamins in bacterial growth that nobody has investigated the influence of Hydrogen ion concentration of media on the growth promoting effect of these factors. The purpose of the present work was to study this relationship.
As tomatoes have been shown by Thjötta and Avery 1 to contain food accessory substances for bacteria, the growth promoting effect of tomato extract adjusted to pH 7.0 upon the growth of B. Shiga in media of pH range 5.4-9.0 was investigated.
It was found 2 that this extract is not able to promote the growth of B. Shiga in broth at initial pH 5.2-6.2, that it has a moderate growth accelerating effect on this microörganism at initial pH 6.6-7.8 and has the best effect when added to broth having a pH 8.2-8.6. Furthermore it may be pointed out that the best growth of B. Shiga, in the presence of tomato extract, occurs at a pH (8.2-8.6) which is by itself an unfavorable one for the multiplication of this microörganism in plain broth.
Before going any further with this investigation it was decided to determine the factor responsible for the growth promoting effect of tomato extract in the case of B. Shiga.
Thjötta and Avery, 1 who used the tomato extract for initiating the growth of Pfeiffer bacillus in blood free media, demonstrated that the poor nitrogen content of tomatoes cannot alone be responsible for the acceleration of bacterial growth.
It seemed necessary to determine whether the high sugar content might be the responsible factor, since it was found that the extract used in these experiments contained 3.54 per cent of reducing substance expressed as glucose. But a quantitative titration of the growth promoting factor of this extract demonstrated that the latter had a pronounced effect when added in a dilution 1 :l00.
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