[HARRISON 4 leck] AESCULIN bile salt MEDIA 107 



The œsculetin then combine with the iron salt (iron citrate) used 

 in the medium to form a dark brown salt. 



The reaction takes place only in sugar-free media. Colonies of B. 

 coli in media containing aîsculin, are black with a black halo around 

 them, and tliey are thus veiy easily seen, and can be readily counted 

 against a white background. 



It is true that other organisms besides B. ooli give the reaction, 

 notably B. lactis aerogenes, lactose fermenting yeasts, and some moulds, 

 but tJie last two may be disregarded, as they are seldom found in water, 

 and the appearance of the colonies is characteristic. B. lactis 

 aerogenes may be regarded as an excreta! form, and hence it is of some 

 benefit to be able to recognize its presence, and with very little practice 

 the appearance of the colonies of this organism on the Eesculin medium 

 may be readily noted, as the colonies are usually larger, moister and 

 more raised than those of B. coli. Some forty species^ or varieties of 

 bacteria and yeasts have been grown in media containing assculin with 

 negative results. B. cloacae is excluded by the sesculin method. 



The preparation of gesculin media is easy, and different lots are 

 very unifonn in composition. Our usual method of preparing is to first 

 weigh out : 



1 or 8 per cent AVitte's peptone 



.5 per cent Sodium taurocholate (commercial). 

 .1 per cent aesculin 

 .05 per cent iron citrate 

 100 c. c. Tap-water 



After steaming from 15 to 30 minutes the medium is filtered and 

 filled into test tubes. 



For œsculin agar 1.5 per cent of agar is used, and after dissolving 

 the agar in part of the water the remaining ingredients are added, 

 brought to the boil and then filtered or else the medium is cooled 

 for the addition of white of egg or albumen, again brought to the boil 

 and then filtered and tubed. 



The tubes may be either sterilized in the steam sitierilizer on three 

 snocessive days, or autoclaved for 15 minutes at 15 lbs. pressure. 



We advise using both bile salt broth and œsculin agar for the 

 routine examination of water, as the former acts as an enrichment 

 method, and the latter indicates the number of colonies of B. coli. pre- 



^B. fluorescens; B. fluor. Itquefaciens; B. prodigiosus; B. lactis viscosns; Slimy 

 milk bacteria, 3 species; B. butyricus; B. Zopfii; Proteus vulgaris; B. mesenterkus; 

 5 species lactic acid bacteria; B. cloacae, one culture from Jordan and one 

 from Johns Hopkins University, etc. 



