BACTERIOLOGICAL ANALYSIS OF WATER 223 



WATER AND SEWAGE MICROBIOLOGY 



EXERCISE 1. BACTERIOLOGICAL ANALYSIS OF WATER 

 FROM A SOURCE NOT SUSPECTED OF SEWAGE 

 CONTAMINATION 



Apparatus. Sterile 500 c.c. flask for collecting water 

 sample; litmus lactose agar shake; twelve tubes of litmus 

 lactose agar; twelve salt-free gelatin tubes; two litmus lac- 

 tose bile fermentation tubes; six agar slants; six tubes of 

 sterile broth; six tubes of Dunham's solution; six tubes of 

 nitrate peptone solution; six dextrose fermentation tubes; 

 six tubes of litmus milk; twelve sterile Petri dishes; sterile 

 100 c.c. volumetric pipette; sterile 1 c.c. and 5 c.c. pipettes; 

 record sheet for recording data obtained; record sheet for 

 recording pure cultures isolated; water sample. 



Cultures. B. coli. 



Water from the local water system should be used for 

 the experiment. This method can be used also for water 

 from deep wells, springs, etc. 



Method. 1. Flush the water pipes thoroughly by 

 allowing the water to run, or by pumping, at least thirty 

 minutes. 



2. Hold the collection flask, mouth downwards, remove 

 the plug and still holding in this inverted position, wash 

 the mouth off with the running water, then fill quickly 

 and replace the plug. The plug must not be laid down 

 during this process. 



3. The sample must be analyzed at once. In routine 

 work, if this is not practicable, place the sample on ice 

 and analyze as soon as possible. Samples kept at 10 C. 

 or less should never be left over a maximum of six hours 

 before analysis. 



4. Plate immediately in duplicate, 1 c.c., 0.5 c.c. and 

 0.1 c.c. of the sample direct in litmus lactose agar and in 

 gelatin (6 plates each). (If sewage contamination is sus- 



