A SIMPLIFIED CONFIRMATORY TEST FOR B. COLI 



REUBEN L. KAHN 



From the Department Laboratory, Southeastern Department, United States Army, 



Atlanta, Georgia 



Received for publication June 17, 1918 



When the presumptive test for B. coli has been estabHshed by- 

 gas production in lactose broth, we have, according to the com- 

 mittee on Standard Methods of Water Analysis (1917), two more 

 steps to carry out before the presence of B. coli is completely 

 confirmed. Transplantations are made from the lactose fer- 

 mentation tubes showing gas, to Endo plates and typical colonies 

 sought for after twenty-four hours incubation. If such colonies 

 be found, the test for B. coli is ''partially confirmed." One or 

 more of these colonies are again inoculated in lactose fermenta- 

 tion tubes and examined for gas production after incubation. 

 The presence of gas in these fermentation tubes renders the 

 presence of B. coli completely established. 



During our investigation of the nature of the reaction of B. 

 coli on Endo medium (1918), it was observed that colonies of 

 B. coli are more typically metallic when grown on Endo agar 

 slants than on inverted Endo plates. This finding has led to 

 the view that possibly test tube slants containing Endo medium, 

 might advantageously be substituted for Endo plates in the 

 confirmatory test for B. coli in water. 



It appeared also that if the inoculation of these organisms in 

 an Endo tube be made both in the butt and on the slant, we 

 would have, after proper incubation, typically metallic colonies 

 on the slant and a practically anaerobic condition in the butt 

 with gas production and reddening of the medium. We should 

 thus have the "partially confirmed" and ''completed" tests for 

 B. coli in one procedure. 



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