The occurrence of Clostridium botulinum and Clostridium tetani in the soil of the United States.

Soil samples taken every fifty miles on four east-west transects across the United States were examined for C. botulinum and C. tetani, organisms that could inhibit the growth of C. botulinum type A, and for various soil properties. Type A strains were found mostly in the western part of the United States, in neutral to alkaline soil. Type B strains were more uniformly distributed, with a majority of them occurring east of the Mississippi River; none, however, were found in samples taken in the southermost transect. They were associated with soil of high organic content. Type C strains were found only in acid soil of the Gulf Coast, and type D strains in alkaline soil of some western states. Type E strains were mostly associated with damp to wet soil. Organisms inhibitory to type A strains were found in 4 of 21 samples of soil in which type A strains were demonstrated and in 7 of 20 samples in which they were not. Trypsin activation of culture fluids was necessary for the demonstration of most strains of types B, C, D, and E. C. tetani was demonstrated in 30 per cent of the soil samples. Its occurrence was not correlated with any particular soil type or climatic area.