424 ORDER IV. EUBACTERIALES 



Key to the genera of family Bacteroidaceae. 



I. Simple, rarely pleomorphic, rod-shaped cells which are strict anaerobes. 



A. Cells with diameters greater than 0.3 micron. 



1. Cells with rounded ends. 



Genus I. Bacteroides, p. 424. 



2. Cells with pointed ends. 



Genus II. Fusobacterium, p. 436. 



B. Cells with diameters 0.15 micron or less. 



Genus III. Dialister, p. 440. 

 II. Highly pleomorphic rods, some of which may be facultative anaerobes. 



A. Strict anaerobes. 



Genus IV. Sphaerophorus , p. 441. 



B. Facultative anaerobes. 



Genus V. Streptobacillus, p. 451. 



Genus I. Bacteroides Castellani and Chalmers, 1919.* 



(Castellani and Chalmers, Man. Trop. Med., 3rd ed., 1919, 959; Ristella Prevot, Ann. Inst. 

 Past., 60, 1938, 289; Capsularis Pr6vot, ibid., 290; Zuberella Prevot, loc. cit.) 



Bac.te.ro.i'des. M. L. noun bader the masculine equivalent of Gr. neut.n. bactrum a 

 staff or rod; Gr. noun idus form, shape; M.L. noun Bacteroides rod-like. 



Rods, with rounded ends, occurring singly, in pairs or in short chains; sometimes pleo- 

 morphic. Some species are encapsulated. Motile and non-motile species occur, the motile 

 species possessing peritrichous flagella. Gram-negative. May or may not require enriched 

 culture media. Usually ferment glucose, rarely lactose or sucrose. Nitrites not produced 

 from nitrates. Gas may or may not be produced in peptone media. Anaerobic. Found in the 

 alimentary and urogenital tracts of man and other animals; some species are pathogenic. 



The type species is Bacteroides fragilis (Veillon and Zuber) Castellani and Chalmers. 



Key to the species of genus Bacteroides. 



I. Non-motile. Sub-genus Ristella Prevot (Ann. Inst. Past., 60, 1938, 289). 

 A. Not encapsulated. 



1. Gas produced in culture media, 

 a. Gelatin not liquefied. 



b. Serum or ascitic fluid not required for growth. 

 c. Attack carbohydrates. 



d. Simple, rod-shaped cells. 



1. Bacteroides fragilis. 



2. Bacteroides frircosus. 



3. Bacteroides perfoetens. 



4. Bacteroides incommunis. 



5. Bacteroides insolitus. 

 dd. Pleomorphic cells. 



6. Bacteroides thetaiotao micron. 



7. Bacteroides trichoides. 



8. Bacteroides terebrans. 



9. Bacteroides halosmophilus . 

 cc. Does not attack carbohydrates. 



10. Bacteroides putidus. 



* Revised by Dr. C. D. Kelly, Department of Bacteriology, McGill University, Montreal, 

 P.Q., Canada, March, 1955. 



