DIFFERENTIATION OF B. COLI AND B. AEROGENES ON 

 A SIMPLIFIED EOSIN-METHYLENE BLUE AGAR 



MAX LEVINE 



From the Laboratory of the Department of Pathology and Bacteriology, State University of 



Iowa, Iowa City, Iowa 



For confirming the presumptive test for B. coli the mediums most 

 frequently employed are litmus lactose agar and fuchsin sulphite 

 (Endo) agar. It is becoming more apparent that the coli-like forms 

 may be divided into two groups which are closely correlated with the 

 source. One group (B. coli) is characteristic of fecal origin; the 

 other (B. aerogenes and B. cloacae) is rare in feces, but constitutes 

 the prevailing coli-like form in the soil and on grains. The standard 

 litmus lactose and Endo agar may be employed to a slight extent for 

 the differentiation of B. coli and B. aerogenes, but the differences 

 between these types on these mediums (particularly L.L.A.) are not 

 very clear-cut nor distinct. Better results are obtained with a modified 

 Endo agar described elsewhere. A very excellent differentiation 

 between the B. coli and B. aerogenes types has been obtained on a 

 modification of eosin-methylene blue agar first described by Holt- 

 Harris and Teague for the isolation of the typhoid group from feces. 

 The medium is prepared in the following manner : 



Distilled water 1000 cc 



Peptone (Difco) 10 gm. 



Dipotassium phosphate 2 gm. 



Agar 15 gm. 



Boil ingredients until dissolved and make up any loss due to evaporation. 

 Place measured quantities in flasks and sterilize at 15 Ibs. for 15 minutes. 

 Just prior to use add to each 100 cc of the melted agar, prepared as above, 

 the following constituents: 



Sterile (20%) lactose solution 1 gm. or 5 cc 



Aqueous (2%) eosin (yellowish) solution 2 cc 

 *_ Aqueous rf%) methylene blue solution 2 cc 



Pour medium into petri dishes, allow them to harden in incubator and 

 inoculate in the ordinary way. Smearing the surface with a glass rod seems 

 preferable to the streaking method sometimes employed. 



There is no adjustment of reaction and filtration of medium is not necessary.. 



B. typhosus and members of intermediate group also grow well on 

 this medium producing transparent, colorless, or slightly amber colonies 

 that are about one-half the size of B. coli. 



Received for publication Feb. 7, 1918. 



