Sbction IV., 1908 [ lOS ] Trans. R. S. C. 



IV. — Aesculin Bile Salt Media for Water and Mill- Analysis. 



By F. C. Harrison and J. van der Leck. 



Bacteriological Laboratories, Macdonald College, P. Q., Can, 



(Read May 26, 1908.) 



The considerable diversity of '" presumptive " tests used in Eng- 

 land and America for B. coli and other excrétai organisms renders an 

 apology almost necessary when introducing yet another test to the 

 attention of laboratory workers. Such a presumptive test (and 

 by this term we mean a simple test wirch will indicate in the 

 majority of cases whether a water contains excrétai organisms or not) 

 largely used in American laboratories is the production of gas in a fer- 

 mentation tube containing dextrose broth, with a gas formula of 

 H : C0,=3 : 1. 



In English laboratories the bile salt broth of McConkey and Hiir or 

 the modification of this medium with neutral red as suggested by Grlin- 

 baum & Hume- is more commonly employed. Phenol broth, lactose- 

 litmus agar, and other media have also been used by various workers. 



Several investigators^ have pointed out the limitations of these tests. 

 Thus in the dase ofi the fermentation of dextrose, that the amount of 

 gas, and the percentage of COo are subject to variation, even with pure 

 cultures of B. coli. and that B. coli is frequently present in fermenta- 

 tion tubes in which the amount of gas was less than 10^ after 48 hours 

 incubation at 37° C. 



Irons'* in an investigation comparing the results obtained with the 

 dextrose fermentation tube and with neutral red broth found in 285 

 determinations 35 percent of positive results with the fermentation tube 

 and 47 per cent of positive results with the neutral red method. Prescott 

 and Winslow ^ in a paper on the relative value of dextrose broth, phenol 

 broth and lactose bile as enrichment media for the isolation of B. coli 

 examined 176 samples of water from various sources. From the data 

 they obtained they considered the bile medium inferior to dextrose broth 

 as an enrichment medium in the process for the complete isolation of 

 B. coli, but as a presumptive test, when the full working out of B. coli 

 was impossible the l)ile medium nfl'ered distinct advantages. Thus they 

 sum up their experimental facts as follows : — 



'^ If the proportion of cases in wliicli B. coli was actually isolated 

 (70 out of tliese 176 sani]j]os) 1)e taken as 100, the percentage of com- 

 plete, positive results, using bile for preliminary enrichment, was 91. 

 If the dextrose broth fermentation test alone had 1)een considered 

 positive 120 "presumptive'' tests would have been obtained, or 171 per 



