Coli-aerogenes bacteria in soils

Abstract

The prevalence of the different types of coli–aerogenes bacteria has been determined in various soils collected from widely separated locations in the United Kingdom and in Denmark. Of the soils examined, 27% contained no coli–aerogenes organisms in 15 g. of soil tested. The number of these organisms in the positive soils was very low; only 11% had confirmed counts greater than 100 organisms/g. and 33% less than 1 organism/g.The most prevalent organism isolated was Bacterium coli type I, whatever the location or vegetation type of the soil; intermediate type I, Bact. aerogenes type I and Bact. coli type II were the only other organisms of numerical importance. The annual application of large amounts of either farmyard or inorganic manures produces no permanently large population of coli-aerogenes organisms in soils.Presumptive tests in MacConkey broth were unreliable, since only 6 % of the positive tubes from hill and moorland soils and 28 % from arable soils were confirmed as containing coli-aerogenes bacteria. Such discrepancies are considered to be partly due to coliform bacteria with weak lactose-fermenting properties.It is considered that there is now sufficient experimental evidence to discredit statements that soil is the natural habitat of Bact. aerogenes or intermediate types of coli-aerogenes organism.