Quantitative Distribution of Psychrotrophic Coliforms in Soil

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In winter, samples of soil were collected from mountain area along the Otake-sawa, branch of the River Tama, from Tokyo and neighbouring areas and from the plateau area in Nagano Pref. Samples of water were also collected from the Otake-sawa. Presumptive coliform counts were obtained by enumerating typical red-coloured colonies formed in the desoxycholate agar plates after 24hr incubation at 30°C. Of 49 soil samples examined, 31 gave a positive presumptive test, but the presence of coliforms was confirmed in only 22 samples. The number of coliforms in the positive soils was fairly low, only 2 samples had presumptive coliform counts greater than 1, 000/g. On the other hand, 7 water samples showed rather consistent coliform counts, ranging from 32 to 310/100ml. Presumptive coliform counts in desoxycholate agar were fairly reliable for water samples, but not so reliable for soil samples. Among 190 coliform strains isolated from winter samples, 179 strains (94%) were psychrotrophic and 151 (79%) of these were IMViC--++, motility positive and gelatine liquefaction negative (Group I). Of 20 soil samples examined in autumn, 19 gave a positive presumptive test, and 16 of these showed positive completed test. Among 113 coliform isolates in autumn 77 strains (68%) were psychrotrophic and 37 (33%) of these were Group I. It was revealed that the majority of coliform strains present in soil is psychrotrophic.
公益社団法人日本食品衛生学会の論文