C. EQUI 469 



Pathogenicity. — C. ovis is a natural pathogen of horses, sheep and perhaps cattle, 

 and is pathogenic for rabbits and guinea-pigs, but not for pigeons or fowls. It produces 

 a soluble toxin which differs from that of C. diphthericB (see above). 



C. pyogenes 



First described by Lucet in 1893. 



Morphology. — The organism is a small. Gram-positive, pleomorphic, diphtheroid 

 bacillus, frequently assuming an almost coccal form, staining irregularly with methylene 

 blue, but apparently without metachromatic granules. 



Growth. — Scanty on plain media, but improved by addition of blood or serum. 

 Grows aerobically and anaerobically. Optimum temperature 37° C. ; Uttle or no growth 

 at room temperature. Optimum pH 7-5. On Loeffler's serum C. pyogenes forms minute 

 colonies in 24 hours at 37° C., which slowly enlarge, if incubation is continued, until they 

 may reach a diameter of 2-3 mm. ; the centre becomes granular and the medium is slowly 

 hquefied, the liquefaction beginning as a small pit beneath each colony. On blood agar 

 colonies, rarely exceeding 1 mm. in diameter, are visible in 48 hours, surrounded by a 

 zone of /S-hsemolysis (Brown and Orcutt 1920, Lovell 1937). In serum broth there is a 

 granular growth without peUicle formation. On gelatin growth is slight, but the medium 

 is slowly hquefied. No growth on MacConkey agar or on potato. 



Biochemical Reactions. — Acid in glucose, maltose, and later in lactose ; occasional 

 strains ferment mannitol and sucrose ; dextrin and glycerol are also said to be fermented 

 (Magnusson 1938). Litmus milk acidified and clotted within 3 days ; clot is later digested. 

 Gelatin, coagulated serum, and coagulated egg albumin are gradually liquefied. Indole 

 negative. Nitrates reduced to nitrites. Filtrable hsemolysin produced, which is most 

 active on horse and rabbit corpuscles and which is destroyed at 56° C. in 30 minutes ; 

 appears to be identical with the toxin ; reaches its maximum concentration in culture 

 in 48 hours at 37° C. (LoveU 1937, 1941). 



Resistance.— Rapidly killed at 57° C, and very sensitive to disinfectants (Brown 

 and Orcutt 1920). 



Antigenic Structure. — Brown and Orcutt studied 12 strains without finding any 

 sharp difference in antigenic behaviour between them. Lovell (1937) studied 33 strains, 

 and except for 5 strains which had been subcultured for some years and which contained 

 a major and a minor antigen, found that, irrespective of animal origin, they appeared 

 to be antigenically homogeneous. 



Pathogenicity. — Under natural conditions produces suppurative lesions in cattle, 

 pigs, sheep, and goats, but not in horses ; is also pathogenic for the rabbit, producing 

 suppurative lesions including arthritis. Experimentally, mice inoculated intraperitoneally 

 with 100-1,000 milhon organisms die in a week with abscess formation in the omentum 

 and Uver. Rabbits inoculated subcutaneously develop localized abscesses ; inoculated 

 intravenously they develop abscesses, particularly in the bones and joints. C. pyogenes 

 forms a weak toxin which, inoculated intravenously into rabbits in a dose of 1 to 5 ml., 

 produces convulsions and death within 30 minutes (Lovell 1937). 



C. equi 



This organism was isolated by Magnusson (1923) from foals affected with pyaemia. 

 It has been confused with C. pyogenes, but differs from it in several respects, notably in 

 its abundant growth on ordinary media, its pigment formation, its failure to Uquefy 

 coagulated serum, to lyse blood, or to ferment carbohydrates, and its pathogenicity for 

 horses. The following description is taken from Magnusson (1938) and Karlson, Moses 

 and Feldman (1940). 



Morphology. — Fairly large, pleomorphic. Gram-positive bacillus, showing meta- 

 chromatic granules ; in pus and surface colonies, may appear coccoid. Reported by 

 some workers to be partly acid-fast. 



