CHAPTER 24 

 STREPTOCOCCUS 



Definition. — Streptococcus. 



Spherical or ovoid cells, arranged in short or long chains, or in pairs. Usually 

 non-motile. Non-sporing. Most species Gram-positive. Some species form 

 capsules. Growth tends to be relatively slight on artificial media, and some species 

 grow poorly in the absence of added native protein. Several species produce 

 characteristic changes in media containing blood. Various carbohydrates are 

 fermented, with the production of acid. Most species fail to liquefy gelatin. Most 

 species are aerobic and facultatively anaerobic ; some are anaerobic. Many species 

 are normally parasitic on man or animals ; some species are highly pathogenic, and 

 some produce soluble toxins. 

 Type species. Streptococcus pyogenes. 



The term Streptococcus was first used by Rosenbach in 1884, when describing a 

 coccus, growing in chains, that had been isolated from suppurative lesions in 

 man. To this organism he gave the name Streptococcus pyogenes. A chain- 

 forming coccus had, however, been described by Fehleisen in the previous year 

 as the causative organism of erysipelas (Fehleisen 1883) ; and Pasteur, Chamber- 

 land and Roux, in 1881, had described a septicsemic infection in rabbits, resulting 

 from the inoculation of these animals with human saliva, which probably affords 

 the earliest recorded reference to the pneumococcus, although no clearly identifiable 

 description of this species was published prior to the independent studies of Fraenkel 

 and of Weichselbaum in 1886. In 1887 Nocard and Mollereau reported the experi- 

 mental production of mastitis in the cow and goat, by the inoculation into the 

 udder of a streptococcus isolated from the milk of a cow suffering from that disease. 

 In 1888 Schiitz described a streptococcus that he had isolated from the lesions of 

 strangles in the horse. In more recent years, chain-forming cocci have been isolated 

 from a variety of pathological conditions in man and animals, from the mouth or 

 from the faeces of healthy subjects, from milk and various milk products, and 

 from other sources. 



The tendency to grow in chains of varying length gives to the members of this 

 group a very characteristic morphology, and they possess in common other char- 

 acters that appear to justify their inclusion in a single bacterial genus. The Com- 

 mittee of the Society of American Bacteriologists (Winslow et al. 1920) separated 

 the pneumococcus from the main streptococcal group, by forming a genus Diplo- 

 coccus, with Diplococcus pneumonim as the type species. It appears to the authors, 

 for reasons which will become apparent, that this separation is undesirable, and the 

 summary of generic characters as set out by the American Committee has been 

 modified in the required sense. As so modified, and with other minor emendations, 

 including the substitution of Str. pyogenes for Str. hcemolyticus as the name of the 

 type species, the description of these generic characters is as given above. 



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