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AN ECOLOGICAL STUDY OF THE COLI‐AEROGENES BACTERIA OF SURFACE SOIL
Author(s) -
THOMAS S. B.,
DRUCE R. G.,
ELSON K.
Publication year - 1960
Publication title -
journal of applied bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.889
H-Index - 156
eISSN - 1365-2672
pISSN - 0021-8847
DOI - 10.1111/j.1365-2672.1960.tb00193.x
Subject(s) - enterobacter aerogenes , incubation , citrobacter freundii , escherichia coli , biology , enterobacter cloacae , bacteria , dominance (genetics) , agar , agar plate , microbiology and biotechnology , veterinary medicine , enterobacteriaceae , biochemistry , medicine , genetics , gene
SUMMARY The coli‐aerogenes organisms content, determined by plating on violet red‐bile agar, of surface soil from a polluted site (heavily grazed pasture) often exceeded 10 4 /g at 30° and 10 3 /g at 37°. Escherichia coli I was present but in a small proportion only. High coli‐aerogenes counts were much less frequent in unpolluted soil (enclosed Forestry Plantation), and E. coli I was relatively rare. The classification of 1,917 strains isolated from colonies on VRB agar at 30° and at 37° showed that Klebsiella cloacae was very much the dominant species in both sites when the plates were incubated at 30°, whereas Citrobacter freundii I and K. cloacae were co‐dominant when incubation was at 37°. E. coli II constituted a relatively high proportion of the strains from both sites but, due to the very marked dominance of these three types, E. coli I was rarely isolated by the method employed, even from the polluted soil. The very high incidence of non‐lactose‐fermenters, particularly among the dominant types, was the outstanding characteristic of the strains isolated, even with incubation at 37°. Only 29% formed acid and gas in MacConkey's broth within 2 days at 37°, while 59% formed acid and gas within 5 days at 30° but failed to do so in 2 days at 37°. There was a much higher incidence of coli‐aerogenes organisms in soil from the unpolluted site during summer than during winter, and this is attributed to possible multiplication of 37° negative strains of the more common types.