284 Disease-Producing Microorganisms 



only Ps. aeruginosa; however, the two organisms can coexist in 

 sterihzed water. Vibrio cholerae does not survive very long in fresh 

 water, although long enough to cause occasional epidemics. 



The addition of typhoid bacteria to a well-moistened and culti- 

 vated soil brings about rapid destruction of the organisms. The 

 same phenomenon occurs when a culture of these organisms is added 

 to that of a soil microbe. An antagonistic relation is often found to 

 exist in some soils but not in others; this is traced to the presence 

 of specific bacteria. Frost reported a marked reduction in numbers 

 of typhoid bacteria added to the soil, 98 per cent of the cells being 

 killed in 6 days. It was suggested that in the course of a few more 

 days all these cells would have disappeared from the soil. On the 

 other hand, under conditions less favorable to the antagonists, the 

 typhoid organism survived not only for many days, but even for 

 months. 



Escherichia coli is rapidly crowded out by other organisms in 

 manure piles and in soil. The dysentery and typhoid organisms dis- 

 appear rapidly, in 12 and 16 hours, in sea water; the paratyphoid 

 organisms have been found to survive for 21 and 23 days. Sea water 

 appears to contain an agent, other than its salts, which exerts a 

 bactericidal effect. 



Under conditions prevailing in southern England, Mycohacterium 

 tuberculosis was found to remain alive and virulent in cow's feces, 

 exposed on pasture land, for at least 5 months during winter, 2 

 months during spring, and 4 months during autumn; in summer, no 

 living organisms were demonstrated even after 2 months; under pro- 

 tection from direct sunlight, the survival period was longer. Bovine 

 tubercle bacteria have been detected in soil and manure, and on 

 grass up to 178 days after infection, but not later. When M. tubercu- 

 losis was added to nonsterile soil, it was slowly destroyed; the plate 

 coimt was reduced to about one-sixth of the original in 1 month. 

 Brucella melitensis survived in sterilized tap water for 42 days, as 

 compared to 7 days in unsterilized water; it survived in sterilized 

 soil 72 days, as compared to 20 days in unsterilized soil. 



In addition to the above pathogenic organisms, others which have 

 the capacity of causing infections or of producing potent toxins in 

 human foodstuffs under proper conditions are found abundantly in 

 the soil. These include the tetanus and gas gangrene organisms, 

 on the one hand, and the botulinus, on the other. These organisms 

 may be present even in virgin soils. 



