Time (hours) Count (per ml) 



2,000 



1 2,000 

 3 2,700 



24 300 



The exercise was repeated with the following results: 



Time (hours) Count (per ml) 



2,100 



22 800 



25 900 

 91 400 



139 300 



In a similar test, a BACT-CHEK disc was incubated in a test tube of 

 water at 35 C for 24 hours, instead of for 2 hours, before it was added 

 to a flask containing 1 liter of filtered autoclaved seawater. Immediately 

 after mixing, the bacterial population of the seawater was approximately 

 200,000 per ml instead of approximately 2,000, as was the case when the 

 discs were incubated for 2 hours. 



In a final laboratory exercise, the effect of added nutrient on E^ 

 coli populations was tested. Ten-ml quantities of a freshly prepared E. 

 coli culture were added to individual 250-ml flasks of filtered seawater 

 and to flasks of seawater containing added tryptic soy broth (a proprietary 

 mixture of nutrients and salts sold by Difco Laboratories, Detroit, MI 

 for preparing culture media for microorganisms). The following coliform 

 counts per ml were obtained. 



Count in Tryptic 

 Time Count in Filtered Soy Broth and 

 (hours) Seawater Seawater 



45,000 35,000 



26 4,000 25 million 



Effect of Ocean Depth on Survival of E^ coli 



Comparisons were made of the numbers of E. coli surviving in seawater 

 cultures exposed for various periods of time at various depths in the 

 ocean. The cultures included E^ coli suspended in filtered autoclaved 

 seawater and in an autoclaved mixture of seawater and human feces. Some 

 of the cultures were contained in 25-ml bags made of cellulose acetate 

 dialyzer tubing tied at each end (Figure 7). The dialyzer bags permitted 

 water soluble substances to diffuse freely between the bags and the 

 ocean but retained the cultures of E^ coli in the bags and prevented the 



