Survival of Listeria monocytogenes in soil

The hypothesis of soil serving as a natural reservoir for Listeria monocytogenes is not un-attractive, since the distribution of the organism over an area ranging from the Arctic to Africa involving man and many other species of animals suggests a common source of infection (Murray, 1955; Seeliger, 1955; in a personal communication, Dr. M. L. Gray, who has kept an up-to-date record of Listeriae isolations, lists 29 animals, 14 birds, and 1 trout). The title of a paper by Olsuf'ev and Petrov (1949) suggests the isola-tion of Listeriae from spring water. Gray (1960) reports the isolation of Listeriae from mice that were fed silage which previously was implicated in listeric abortion of cattle. Although the organism has not been found in the soil, some have considered it possible (Seeliger and Cherry, 1957). The present paper is concerned with the survival of L. monocytogenes in soil under ex-perimental conditions. MATERIALS AND METHODS L. monocytogenes of the serotype 1 was used in these experiments. Cells were grown on tryptose blood agar base (Difco) containing 1 per cent glucose. Inocula for soils and other materials were prepared by growing the Listeriae on the above medium for 24 hr at 34 C, after which time the cells were harvested and washed three times in distilled water by centrifugation. The organisms were allowed to remain in the distilled water only as long as necessary to perform the washing and complete the inoculations. To represent extremes, two types of soil were selected: clay soil and fertile garden soil. A batch of each type was collected and stored in sealed vessels; therefore all samples were portions of the same specimens throughout the studies. Soil (3 g) was placed in test tubes, 20 by 12