SUMMARYA variety of factors that affect lecithinase activity and lecithinase production byCl. welchiiwere studied. The lecithinase activity was time and temperature dependent. The optimum temperature varied from 30° to 46° C. according to the strain ofCl. welchiiemployed. Maximum lecithinase activity was produced after 12–60 hr. There was considerable strain variation. This could easily account for the differences in the published data.Commercial purified lecithinase was more readily destroyed by heat than the lecithinase produced byCl. welchiiin culture media. The enzyme inactivation pattern at 60° C. was similar to that at 90° C. This is not in agreement with the reports of others who found that less enzyme was inactivated at the higher temperatures.Acid pH values completely inactivated the enzyme. However, alkaline pH values did not significantly destroy the enzyme. The lecithovitellin reaction was completely inhibited at pH values of 1–5. The optimum pH for the reaction was around pH 7–8.The production of lecithinase was dependent upon the pH of the culture medium. One strain produced measurable lecithinase at pH values of 5·5–8·5, whereas another strain produced lecithinase only at pH values 6–5–7–5.Lecithin stimulated the production of lecithinase in a chemically defined medium.

SUMMARYThe lecithinase and haemolytic activity of thirty strains ofCl. welchiiisolated from food, faeces, and soil, was studied. The strains from foods produced smaller amounts of lecithinase and were, in general, less haemolytic than the strains isolated from soil and faeces.The haemolytic activity ofCl. welchiion erythrocytes from different animal species displayed considerable variation. Sheep erythrocytes were the most sensitive to the action of alpha toxin, whereas rabbit blood was most sensitive to haemolysis by theta toxin. The degree of haemolysis was also dependent upon the concentration of the enzyme, and temperature and length of incubation.The haemolytic activity of commercial lecithinase was observed to be similar to the haemolytic activity of the alpha toxin ofCl. welchii. This finding provides further evidence that the haemolytic and lecithinase activities ofCl. welchiiare due to one substance, the alpha toxin. Exposure of commercial lecithinase to heat resulted in the destruction of its haemolytic properties.

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