600 STREPTOCOCCUS 



Streptococci of the Viridans Group 



Morphology. — Cocci in short or long chains, spheroidal or ovoid ; when ovoid, long 

 axis in axis of chain. Non-capsulated. No spores. Non-motile. Gram-positive. Not 

 acid-fast. 



Growth Requirements. — Most strains grow more readily on ordinary media than 

 does Sir. 'pyogenes or Str. pneumonice, but growth is usually improved by addition of 

 blood or serum. Some strains, on the other hand, grow very poorly. Optimal temperature 

 for most strains 37° C— -the range of temperature for growth extends further than that of 

 Str. pyogenes or Str. pneumonice in the downward direction. Aerobic and facultatively 

 anaerobic. 



Type of Growth. — On solid media the colonies do not differ in any distinctive way 

 from those of Str. pyogenes (see above). With streak cultures, the growth may be 

 slightly more profuse, and more confluent. 



In blood agar plates. — The colonies are surrounded by a zone of a-hsemolysis, showing 

 the characteristic green coloration. 



In broth. — The type of growth varies with chain length. Many strains or varieties 

 grow in short chains and produce a uniform, but slightly granular, turbidity in broth, 

 with little or no deposit ; but some strains grow in long chains and give growths which are 

 indistinguishable from those of Str. pyogenes. 



On gelatin, or in gelatin stab, the growth does not differ from that of Str. pyogenes, 

 except that it may be slightly more profuse. 



On potato, growth is slight, and often not detectable by the naked eye. 



Heat Resistance. — Most strains are killed by heating at 55-58° C. for 30 minutes. 

 The general vitality is greater than that of Str. pyogenes. 



Biochemical Reactions. — Milk is acidified, and often clotted. Most strains produce 

 acid from lactose and saccharose, often from raffinose and/or salicin, rarely from inulin 

 or mannitol. Nitrates are not reduced. Indole is not formed. Gelatin is not liquefied. 

 Not soluble in bile. 



Pathogenicity and Toxin Formation. — Viridans streptococci form no soluble toxin, 

 nor haemolysin. Usually non-pathogenic for laboratory animals other than the rabbit, 

 in which some strains give rise to arthritis and valvular lesions. They are a common cause 

 of subacute ulcerative endocarditis in man. 



Differentiation within the Group. — The viridans group of streptococci certainly 

 contains more than a single species. It is possible that the common streptococcus of the 

 human mouth, which has the peculiar property of producing a soluble levan from sucrose 

 and raffinose and of forming large mucoid colonies when grown on agar containing 5 per cent, 

 of these sugars, deserves specific rank with the title Str. salivarius ; that the common 

 streptococcus of bovine faeces should be recognized as Str. hovis ; and that a streptococcus 

 isolated from Kefir, which produces COj from lactose when grown in Eldridge tubes shoxild 

 be known as Str. kefir. Our knowledge is, however, not yet sufficient to allow us to define 

 species or to assign specific names with any degree of certainty. 



Str. fsecalis 



Morphology. — Ovoid cocci, growing in pairs or short chains. Some strains resemble 

 the pneumococcus in morphology, but possess no capsule. More rarely, the appearance 

 may be almost bacillary. Most strains non-motile, but a few motile strains have recently 

 been described. No spores are formed. Gram-positive and not acid-fast. 



Growth Requirements. — Grows well on the ordinary laboratory media. Optimal 

 temperature about 37° C., but grows well up to 45° C. and do\Yn to 10° C. Aerobic 

 and facultatively anaerobic. 



Type of Growth. On solid media, the colonies are somewhat larger than those of the 

 species referred to above. After 24 hours the colonies are usually 0-75 mm. in average 



