Survival of shigellae in soil

The survival of four Shigella strains in soil (Sh. sonnei, Sh. boydii, Sh. flexneri and Sh. dysenteriae) was studied under various conditions. Their survival period was tested in two different types of sterile soil at 18-20 degrees C and in one type of soil at 4 and 37 degrees C. This latter type of soil, after enrichment with casaminoacids or (NH4)2HPO4 was also used for testing again the survival of the strains at 18-20 degrees C. Though the initial number of the inoculated microorganisms was quite high (10(7) to 10(8) micr. per g of soil) the survival periods were generally short (6 to 39 days). It was found that their viability depended mainly on the bacterial species and not so much on the type of soil, enriched or not, and the temperature. Thus the survival period in soil was always longer for Sh. sonnei and Sh. boydii and shorter for Sh. flexneri and Sh. dysenteriae. The incubations at 4 degrees C or in enriched soil increased and in 37 degrees C decreased the longevity of the strains but for a few days.