The comparative effect of two organophosphorus pesticides (chlorophos and metaphos) on Escherichia coli, an enterococcus and Shigella organisms present in chernozem, podzolic, and loamy soils was investigated. A considerable level of resistance of the test organisms to the insecticides was established. This was expressed by their behaviour only changing on contamination of the soil samples with the insecticides in amounts considerably exceeding those used in natural conditions. Escherichia coli stand much closer to Shigella organisms than the enterococcus does as regards resistance to the insecticides studied. This allows Escherichia coli to be evaluated as an organism of hygienic value under conditions of soil contamination by pesticides. The enterococcus, in the present concrete case, was a less indicator microorganism than was Escherichia coli.

Inductive effects of environmental concentration of atrazine on Escherichia coli and Enterococcus faecalis