FAMILY IV. EXTEROBACTERIACEAE 335 



Keij to the genera of tribe Escherichieae. 



I. Alginic acid is not decomposed with the production of acid and gas. 



A. Lactose is fermented icithin 48 hours. 



1. *Acetylmethylcarbinol not produced; methyl red test positive; salts of citric 

 acid may or may not be used as sole sources of carbon. 



Genus I. Escherichia, p. 335. 



2. *Acetylmethylcarbinol produced; methyl red test negative; salts of citric acid 

 used as sole sources of carbon. 



a. Usually not encapsulated; from feces, milk, dairy products, grain and other 

 saprophj^tic sources. 



Genus II. Aerobacter, p. 341. 

 aa. Usually encapsulated; from respiratory, intestinal and urogenital tracts. 

 Genus III. Klebsiella, p. 344. 



B. Lactose fermentation is consistently delayed, and occasionally lactose is not fer- 

 mented at all. 



Genus IV. Paracolobactrum, p. 346. 

 II. Alginic acid is decomposed with the production of acid and gas. 



Genus V. Alginobacfer, p. 348. 



Genus I. Escherichia Castellani and Chalmers, 1919.] 



(Castellani and Chalmers, Man. Trop. Med., 3rd ed., 1919, 941; Citrobacter Werkman and 



Gillen, Jour. Bact., SS, 1932, 173; Enterobacter Rahn (in part), Cent. f. Bakt., II 



Abt., 96, 1937, 281.) 



Esch.er.i'chi.a. M.L. gen. noun Escherichia of Escherich; named for Prof. Theodor 

 Escherich, who first isolated the type species of this genus. 



Short rods. Motile or non-motile. Gram-negative. Glucose and lactose are fermented 

 with the production of acid and gas. Acetylmethylcarbinol is not produced. Methyl red test 

 positive. Carbon dioxide and hydrogen are produced in approximately equal volumes from 

 glucose. Generally not able to utilize uric acid as a sole source of nitrogen. Found in feces; 

 occasionally pathogenic to man (enteritis, peritonitis, cystitis, etc.). Widely distribu- 

 ted in nature. 



The type species is Escherichia coli (Migula) Castellani and Chalmers. 



Key to the species of genus Escherichia. 



I. Citric acid and salts of citric acid are not utilized as sole sources of carbon. Hydrogen 

 sulfide not produced. 



A. Usually not pigmented although a yellow pigment is sometimes produced. 



1. Escherichia coli. 



B. Golden brown to red pigment produced. 



2. Escherichia aurescens. 



II. Citric acid and salts of citric acid are utilized as sole sources of carbon. 



A. Hj'drogen sulfide produced. 



3. Escherichia freundii. 



B. Hydrogen sulfide not produced. 



4. Escherichia intermedia. 



* Levine (Jour. Bact., 1, 1916, 153) was the first to show the inverse correlation between 

 the methyl red and Voges-Proskauer tests and used these characters for the primary sep- 

 aration of the Escherichia coli section from the Aerobacter aerogenes section of the coliform 

 group (Amer. Jour. Public Health, 7, 1917, 784). 



t Prepared by Prof. M. W. Yale, New York State Experiment Station, Geneva, New York, 

 July, 1943; revised by Prof. Robert S. Breed, Cornell University, Geneva, New York, in 

 consultation with investigators that have made special studies of this genus, October, 1955. 



