SURVIVAL OF PATHOGENS IN SOIL AND WATER 



31 



outside the host has been studied in detail. Sufficient information has 

 been accumulated, however, to justify certain general conclusions. 

 When E. coli is added to sterile soil, it multiplies at a rapid rate, but 

 when added to fresh, nonsterile soil it tends to die out quickly (Table 5 ) . 

 The rate of its disappearance is independent of the reaction of the soil 

 and of the temperature of incubation, but a marked increase in the num- 

 ber of soil organisms antagonistic to E. coli accompanies the disappear- 

 ance (Table 6). 



TABLE 5. SURVIVAL OF BACTERIA ADDED TO SOIL AND THEIR EFFECT 

 UPON THE SOIL MICROBIOLOGICAL POPULATION 



From Waksman and Woodruff (951). 



* In thousands per gram of soil. 



t Washed suspension of E. coli cells added at start and after 5 days. 



i CaCOs added to soil. 



TABLE 6. INFLUENCE OF ENRICHMENT OF SOIL WITH ESCHERICHIA COLI 

 ON NUMBER OF ANTAGONISTIC MICROORGANISMS 



Control soil 



Enriched soil 



Enriched soil + CaCOgf 



TOTAL MICRO- 

 ORGANISMS PER 

 GRAM OF SOIL 



ANTAGONISTS* PER GRAM OF SOIL 



After 65 days After 1 1 7 days After 1 1 7 days 



500,000 

 4,000,000 

 6,000,000 



1,150,000 

 5,700,000 

 4,700,000 



9,100,000 

 40,000,000 

 36,300,000 



From Waksman and Woodruff (949). 



* An antagonistic colony is one surrounded by a halo on the E. coli plate. 



t This container received fewer enrichments with E. coli than the one without CaCOj 



