Abstract
The dissimilation of lactose and sucrose by Shigella paradysenteriae var. Sonne has been studied to gain additional knowledge of the phenomenon known as “delayed” or “slow” fermentation. The culture (A.T.C. 31) shows in lactose and sucrose the delayed fermentation characteristic of the Sonne type. In Durham fermentation tubes about 4 days are required for acid formation in lactose broth and about 7 days for sucrose. Colonies on lactose or sucrose agar plates are alkaline or neutral but after a few days develop small secondary colonies as papillae which become acid. If a papilla on sucrose or lactose agar is suspended in sterile broth or saline and plated on agar containing the same sugar, 2 types of colonies appear. One type is acid and does not form papillae even after long incubation, the other type is like the original, alkaline and develops acid papillae. Sugar broth inoculated with the acid type colony is promptly acidified, whereas the alkaline type causes the characteristic delayed fermentation.
Attempts to decrease the time for acid formation in the slow culture by transferring once or twice daily to fresh medium with the same sugar have failed, though this procedure has been carried through 60 transfers. One may easily obtain the rapid variant, however, by plating out a culture which has developed acid, the types of colonies developing on the plates being of 2 types, acid and alkaline, as when the papillae from plate cultures are used.
In order to study the fermentation of lactose and sucrose in more detail than was possible using Durham tubes, flasks have been used, and examination made at least once daily to determine pH, titrable acidity, oxidation-reduction potential, sugar utilized, total population and per cent of population composed of the rapid fermenting variant.
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