THE HEMOLYTIC STREPTOCOCCI : GROUP D 583 



They give a low final pH in glucose broth (4-0-4-8). They grow freely on 10 per cent, 

 and 40 per cent. bUe agar. They reduce methylene blue in milk. They are heat-resistant, 

 withstanding a temperature of 60° C. for 30 minutes. They fail to hydrolyse sodium 

 hippurate. They ferment lactose, saUcin, nearly always mannitol, and usually but not 

 always trehalose and sorbitol. 



^ Enterococci. — Many bacteriologists, especially of the French school, have long recog- 

 nized the occurrence in the human intestine of a characteristic streptococcus, usually 

 occurring in pairs of ovoid cocci, sometimes in short chains. The characteristic morphology 

 of this organism was described by ThierceUn in 1899, who called it the Enterococcus ; 

 and under that name it has made frequent appearances in later Uterature. 



The interrelation of the streptococci of the human intestine has been studied by Dible 

 (1921), whose paper on this subject affords an admirable example of the methods which 

 should be employed in differentiating bacterial groups. He tested 13-4 strains of strepto- 

 cocci from human ffeces as regards their behaviour in a large number of biological tests, 

 including heat resistance (see Houston and McCloy 1916) and chain formation as well as 

 various biochemical reactions ; and measured the association between different pairs of 

 reactions by calculating a statistical coefficient of association. Using one such coefficient, 

 which gives the value of -|- 1 where the association between two characters is absolute, 

 where there is no association, and — 1 where the characters are mutually exclusive, he 

 obtained the following values for the association between a particular series of characters 

 among his 134 strains : 



Heat resistance and mannitol fermentation . . . . -|- 0-93 



,, ,, ,, raffinose fermentation . . . . — 0-85 



„ ,, ,, chain formation . . . . . — 0-96 



Mannitol fermentation and chain formation . . . . — 0-93 



Heat resistance, as here designated, was tested by the ability of the various strains to 

 survive heating at 60° C. for 30 minutes. Those organisms were classed as chain-formers 

 which showed any wide departure from the diplococcal form. Dible thus succeeded in 

 demonstrating the existence in human faeces of a characteristic group of organisms which 

 possessed a predominantly diplococcal morphology, were unusually resistant to heat, 

 almost always fermented mannitol, and very seldom fermented raffinose. It may be added 

 that the streptococci belonging to this group constantly fermented salicin, very seldom 

 fermented inulin, and gave good growth on gelatin at 22° C. About 10 per cent, of them 

 liquefied gelatin. None of them caused hfemolysis in blood agar, or produced a green 

 pigment. In a later communication (Weatherall and Dible 1929), it was noted that some 

 strains of enterococci, having all the characters referred to above, produced areas of 

 haemolysis when grown on blood agar plates ; but no filtrable haemolysin could be obtained 

 by the usual methods of cultivation. It seems clear that these hsemolytic strains correspond 

 to the " Group D " haemolytic streptococci referred to above. 



It has already been noted that streptococci from the human fseces grow freely in the 

 presence of bile (Weissenbach 1918) and reduce methylene blue in milk. They have 

 also been shown to produce a low final pH in glucose broth (Sherman and Stark 1931), 

 to grow at both 10° and 45° C, and to develop in skimmed milk containing 1 : 1,000 

 methylene blue. Most strains belonging to this group produce no change on a blood 

 agar medium, though a few have been described as forming a-hsemolytic or /S-hsemolytic 

 colonies. According to Ehrismaim (1943) the effect on blood is variable. 



Lactic streptococci. — Giinther and Thierfelder (1895) described the occurrence in milk 

 of an organism which was responsible for spontaneous souring and clotting. They described 

 the organism as a short baciUus ; but Heinemann (1906), when investigating the bacterial 

 flora of milk some ten years later, pointed out that a particular streptococcus, which was 

 almost constantly present in fresh milk, was probably identical with the organism of 

 Giinther and Thierfelder. Baelir (1910) confirmed the frequent presence of this strepto- 

 coccus and noted that it produced a large amount of acid, and rapid clottuig. Ruediger 



