562 STREPTOCOCCUS 



capsulated to some degree. Capsulation is, however, very irregular, occurring in 

 some types and not in others, and seems to be affected by the amount of hyaluronic 

 acid in the substrate and the amount of hyaluronidase secreted. Generally speak- 

 ing, capsulation and the secretion of hyaluronidase apjjear to be mutually exclusive 

 (McClean 1941, 1942), and there is no constant association of capsulation with 

 virulence. 



From time to time, accounts have appeared in the literature of motile strepto- 

 cocci, but many of these have been based on somewhat inadequate observations, 

 and the genus Streptococcus has, until recently, been regarded by most bacteriologists 

 as composed exclusively of non-flagellated species. It is certain that flagellated 

 forms are very rare ; but two observers (KoblmuUer 1935, Pownall 1935) have 

 recently given careful and detailed descriptions of motile strains of streptococci. 

 In each case the organism described was apparently a motile variant of the species, 

 or group, that is generally known by the name of " enterococcus." 



Streptococci stain readily with the ordinary dyes ; none of them is acid-fast ; 

 and the great majority are frankly Gram-positive. Some strains tend to lose the 

 Gram stain if decolorization is prolonged ; a few species, or varieties, have been 

 described as frankly Gram-negative. 



Cultural Requirements. — Some species of streptococci, such as Str. pneumonice 

 and to a less extent Str. pyogenes, grow poorly on the simpler media of the laboratory 

 when first isolated ; though they can usually be trained to grow on these media 

 after a limited number of subcultures. The growth of these species is markedly 

 improved by the addition to the medium of such materials as blood or serum. 

 A few species, or types, such as the enterococci, grow well in the presence of bile 

 or bile salts, while most do not. 



The optimal temperature for growth is, with most parasitic species, in the near 

 neighbourhood of 37° C. Some species found in milk have an optimum about 

 30° C. The range over which growth occurs is, for the more sensitive species, 

 somewhat restricted ; 42° C. or thereabouts marks the upper limit ; growth is 

 usually slow at temperatures below 30° C. and often ceases below 20° C. Some 

 species, on the other hand, including certain streptococci found in milk, grow 

 actively at temperatures of 45° C. or over (see Sherman and Stark 1931). Such 

 thermophilic types are of considerable economic importance in relation to pasteuriza- 

 tion (see Chapter 93). 



Most species are aerobic and facultatively anaerobic. Some are strict anaerobes, 

 or microaerophilic. It will be more convenient to discuss the other characters of 

 these anaerobic streptococci, which have not yet been studied in any detail, in a 

 separate section of this chapter (p. 596). Pneumococci grow best in an atmosphere 

 containing 10 per cent, carbon dioxide ; some strains are said not to grow at all 

 in its absence (see Fleming 1941, Kempner and Schlayer 1942). Glutamine is 

 said to be required for the growth of Group A but not of Group B hsemolytic 

 streptococci (Fildes and Gladstone 1939). For a fuller account of the growth 

 requirements see p. 66. 



These cultural requirements, while supplying useful ancillary evidence in 

 identification, do not, except in the case of the anaerobic species and the markedly 

 thermophilic streptococci, afford an adequate basis for any primary classification. 



Growth Characters. — On solid media the streptococci tend to form small, discrete, 

 slightly raised colonies, 1 mm. or less in diameter. The modal colonial form varies 

 in different species ; and it may in some cases be sufficiently characteristic to assist 



