592 STREPTOCOCCUS 



with Group C streptococci, but not with Group A streptococci. There is some evidence 

 that the virulence of Group A strains is more closely related to the type-specific M protein 

 than to the possession of a capsule (see Lancefield 1941). The importance of hyaluronidase 

 is hkewise doubtful. Neither Crowley (1944) who studied 376 strains of hsemolytic strepto- 

 cocci from human sources, nor Humphrey (1944) who studied 81 strains of pneumococci 

 from consecutive cases of pneumonia, could find any relation between the amount of 

 hyaluronidase produced and the apparent virulence of the strain. 



In summary, Str. pyogenes produces the following toxms or aggressive substances 

 (see Chapter 48) which, in one way or another, determine or are associated with its patho- 

 genic activity : (a) hsemolysin, (6) leucocidin, (c) erythrogenic toxin, {d} fibrinojysin, (e) 

 hyaluronic acid, (/) hyaluronidase, (g) type-specific M protein. 



Str. agalactise.' — Our knowledge of the pathogenicity and toxigenicity of this species 

 is, as yet, very incomplete. It produces mastitis in cattle, but, so far as our present 

 knowledge goes, is not pathogenic for man. Its pathogenicity for the mouse, or the rabbit, 

 is low (Minett and Stableforth 1931, Minett 19356). Some, but not all, strains, produce 

 a filtrable hsemolysin, which Todd (1934) has found to be of the oxygen-stable, non-antigenic 

 type. Whether Str. agalactice produces a leucocidin is not knowTi. It has been shown by 

 Smith (1929) that strains of hsemolytic streptococci isolated from cattle may produce an 

 erythrogenic toxin that is neutralized by scarlatinal antitoxin ; but there is no evidence 

 that these strains were Str. agalactice. No erythrogenic toxin was produced by the mastitis 

 strains examined by Minett and Stableforth (1931). Str. agalactice does not produce a 

 fibrinolysin active against human fibrin (Lancefield and Hare 1935, Hare 1935), or against 

 cattle fibrin. It produces hyaluronidase, but seldom forms capsules ; when it does, the 

 capsules do not consist of hyaluronic acid (MoClean 1941). 



Str. pneumoniae. — The pneumococcus is an important pathogen of man, giving rise 

 to pneumonia, particularly the lobar form, sinusitis, otitis media, less fi'equently meningitis, 

 suppurative arthritis, or peritonitis, and occasionally other infections. 



It is highly pathogenic for the mouse and rabbit, rather less so for the guinea-pig. 

 The cat, dog and chicken are relatively resistant. It is a characteristically invasive . 

 organism, causing a fatal bactersemic infection when injected intravenously, an acute 

 peritonitis followed by bactersemia when injected intraperitoneaUy, locaHzed sujjpuration 

 followed by generaUzation when injected subcutaneously, and a spreading inflammatory 

 lesion followed by generalization when injected intradermally in the rabbit. Different 

 serological types of pneumococci may show differences in their virulence for different 

 laboratory animals ; for instance, many strains of Type III pneumococcus are relatively 

 avirulent for the rabbit (Tillett 1927). Again, different strains belonging to the same type 

 may show wide variations in virulence as judged by their minimal lethal dose. With a 

 strain of maximal virulence the injection of 1-10 pneumococci into the peritoneum of 

 a mouse will cause an infection that leads to death within 18-48 hours. 



In contrast to Str. 'pyogenes, the pneumococcus is not an actively toxigenic organism, in 

 the sense of producing filtrable toxins. Some observers have, indeed, regarded it as being 

 devoid of this capacity, and as affording a typical example of a bacterium the pathogenicity 

 of which is determined entirely by its powers of invasion, associated, of course, with the 

 effects of those presumptive " endotoxins " (see Chapter 44) that must always be concerned 

 in invasive bacterial infections. There is little doubt that this contrast is a true one, in 

 the sense that filtrable toxins play a much more prominent part in Str. pyogenes infections 

 than in those due to pneumococci ; but the difference is not so absolute as it has been 

 supposed to be. 



We have seen that Str. pneumonice produces a filtrable hsemolysin when grown under 

 optimal conditions. This is of the oxygen -sensitive type, and is antigenic. There is 

 evidence (Todd 1934) that it bears some antigenic relationship to the oxygen-sensitive 

 hsemolysin of Str. pyogenes, but is certainly not identical with it. Oram (1934) has 

 described the presence in pneumococcal filtrates of a leucocidin, active for rabbit leucocj^es. 

 Like the streptococcal leucocidin described by Gay and Oram (1933), this substance is 



