Clostridium botulinum in the lakes and waterways of London

Mud samples collected during 1974 from a large proportion of the lakes and waterways of London were examined for Clostridium botulinum. Of 69 such sites, 50 (72.5%) contained at least one type of the organism. Of the 50 positive sites, 31, 12, 1 and 10 contained, respectively, types B, C, D and E. Most of the demonstrations of type B required trypsinization of culture filtrates. An examination of 7 lakes in Edinburgh, made for the purpose of comparison, showed that 4 contained type B and one type C. An analysis of the results gave quantitative information on the value of (1) resampling apparently negative lakes, (2) the use of both heated and unheated culture inocula, and (3) trypsinization of culture filtrates.