DETECTION OF B. COLI IN WATER. 



137 



MacConkey has devised bile-salt media, which he claims is of great aid 

 in identifying B. coli and its close relations. Incubation must proceed at 

 42° C. 



A. Bile-salt Agar. 



Agar 1.5 grms. 



Sodium taurocholate (pure) .5 „ 

 Peptone . . . . 2.0 „ 

 Water . . . loo.o c.c. 



This is boiled, clarified, and 



filtered as usual, then, 

 Lactose . . . .1.0 grm. 



is added, and the medium tubed and 



sterilised for three successive days in a 



Koch steriliser. 



B. Bile-salt Broth. 



Sodium taurocholate (pure) 0.5 grms. 

 Peptone .... 2.0 „ 

 Glucose . . . . 0.5 ,, 

 Water .... loo.o c.c. 



Boil, filter, and add sufficient neutral 

 litmus; fill fermentation tubes (Smith's 

 or Durham's) and sterilise as usual in 

 Koch steriliser. 



In the agar medium the surface colonies of B. coli are found to be large, round, 

 whitish, with yellow centres and quite opaque, whilst in the medium surrounding the 

 deep colonies is a distinct hazy halo around each, which soon diffuses throughout the 

 entire medium, if the deep colonies are at all numerous. The high temperature of 

 incubation, in combination with the ingredients, proves unfavourable to develop- 

 ment of bacteria other than intestinal forms. Griinbaum and Hume advise the addi- 

 tion of I per cent of a half per cent watery solution of neutral red to this medium, 

 its qualities being thereby greatly enhanced. Surface colonies of B. coli, and the 

 medium in their immediate locality, are coloured a bright violet-red, whilst the typhoid 

 colonies are yellowish-white, and the medium surrounding them assumes an amber 

 hue. This reaction is very sharp if the medium, before sterilisation, is standardised 

 by adding .4 cc. normal sodium hydrate solution per litre, after making neutral to 

 litmus. Where the broth is used, gas-formation and cloudiness betoken the presence 

 of B. coli; in absence of gas-formation, cloudiness may point to the presence of 

 B. typhosus or B. fcecalis alkahgenes, which can readily be confirmed, or not, by the 

 usual means of identification. 



The whole question turns on the possibility of recognising 

 bacteriologically the contamination of water with sewage. 

 Klein and Houston here insi.st on the fact that in crude sewage 

 the B. coH or the members of the coU group are practically 

 never fewer than 100,000 per c.c, and therefore if in a water 

 this organism forms a considerable proportion of the total 

 number of organisms present, then there is grave reason for 

 suspecting sewage pollution. As, however, this organism is 

 fairly widespread in nature, they hold that valuable supporting 

 evidence is found in the presence of the B. enteritidis sporogenes 

 and of the streptococci, both of which are probably constant 

 inhabitants of the human intestine. The spores of the former 

 usually number 100 per c.c. in sewage, and the presence of the 



