TWO NEW TYPES OF RIBOFLAVIN-DECOMPOSING BACTERIA ISOLATED FROM HUMAN FECES

Abstract

1. Stool samples were cultured for 2 weeks in glucose-broth media containing 5mg/100ml riboflavin, those showing a decrease in riboflavin up to below 3mg/100ml were assumed to be positive for riboflavin-decomposing bacteria.
The incidence of positive stool was 6.3per cent, most frequent in elderly subjects, followed by children under 10 years of age. It was not found in breast-fed infants.
2. Two strains of riboflavin-decomposing bacteria, 14 I and A I, were isolated in a pure state from one stool sample showing marked riboflavin decomposition.
3. The 14-I strain is a motile, non-spore-forming, Gram-positive rod which alone markedly decomposes riboflavin.
4. The A-I strain, too, is a motile, non-spore-forming, Gram-positive rod but differs in toto from the 14-I strain both bacteriologically and immunologically.
The riboflavin-decomposing activity of this bacterium alone is weak but when cultured together with the A-IV strain, isolated from the same stool sample, a marked decomposition of riboflavin takes place.
The A-IV strain is a motile, non-spore-forming, Gram-positive rod, which alone does not break down riboflavin.
5. The break down product of all these riboflavin-decomposing bacteria is lumichrome. Riboflavin decomposition is accelerated in shaking culture, but no decomposition occurs when glucose is added to the medium.