Studies on the sulfite reduction test for clostridia.

Peptone-yeast extract (PY) medium containing 0.035% ferric ammonium citrate as an indicator, 0.05% sulfite as a substrate, 0.05% cysteine as a reducer and 0.5% glucose was found to be suitable for observing the sulfite reduction test. The effect of added cysteine on the test was suppressed by the addition of glucose. In cultures of bacteria grown for 2 days at 37 C in medium containing the above ingredients, 121 among 132 strains of clostridia, including 86 strains of Clostridium perfringens, gave a positive reaction. Although some strains of Salmonella and Proteus were positive, the specificity of the test for clostridia was thought to be relatively high. Positive reactions in a resting cell system were limited to some species of clostridia.