358 MEDICAL BACTERIOLOGY 



CHAPTER X 



DETECTION OF PATHOGENIC BACTERIA IN 

 WATER AND MILK SUPPLIES 



EXERCISE 108. EXAMINATION OF WATER FOR PATHOGENIC 



BACTERIA. 



It is rarely necessary to test water directly for either the typhoid 

 or cholera organisms, as there is little chance of their being found 

 except in the most grossly polluted waters. What is usually sought 

 for is evidence of sewage pollution.. If this is found the water is 

 not regarded as potable. The more common methods of detecting 

 fecal bacteria have already been given (Chapter V). The follow- 

 ing methods are reliable and the detection of these germs in artifi- 

 cially infected waters furnish most excellent practice for the student. 



Bacillus typhosus. In the examination of water it is best to con- 

 centrate the bacteria by filtering a large amount of the water through 

 a Berkefeld filter and to use the slime on the filter to make the plates. 



a. Parietti's method, see 103. 



h. Hiss' method. Make plate cultures and incubate at 38° C. 

 for 18 hours. Inoculate suspicious colonies into Hiss ' tube medium, 

 fermentation tube and milk. Also make indol test and try Widal 

 reaction. 



c. Animal Inoculation. (Michigan method.) 



1) Inoculate suspected water into bouillon tubes or flasks, and 

 incubate at 38° C. 



2) Twenty-four to forty-eight hours later inoculate one cc. into 

 the peritoneal cavity of a white rat. 



3) If animal recovers B. typhosus is not present. If animal dies 

 hold autopsy and isolate and study organism causing death. 



Microspira comma. 



a. If there be a reason to believe that the spirilla are very numer- 

 ous gelatin plate cultures can be made directly from the water, and 

 the suspicious colonies worked up. 



