THE CLASSIFICATION OF THE Oi-H^MOLYTIC STREPTOCOCCI 589 



but we doubt very greatly wbether it is yet possible to define with any exactitude 

 either an inclusive species Str. viridans, or any of the fermentative types that have 

 in the past been given specific names. We may, however, mention some of the 

 properties attributed to the main types. 



Str. salivarius. — This organism occurs in the human mouth and intestine. It is said 

 to form short chains, to grow at 45° C. but not at 10° C, to produce very Uttle greening 

 on blood agar, to produce a low final acidity (pH 4-0-4-4) in glucose broth, to clot mUk, 

 to form a soluble levan from sucrose and raffinose, to give rise to large mucoid colonies 

 on agar containing 5 per cent, of either of these sugars, to ferment lactose, raffinose and 

 sahcin, and to hydrolyse sesculin but not sodium hippm-ate (Niven et al. 1941, Sherman 

 et al. 1943). Most workers record it as being without action on inuhn, but Sherman, 

 Niven and Smiley (1943) include this sugar among those that are fermented. 



Str. mitis. — This organism also occurs in the human mouth. According to Sherman, 

 Niven and Smiley (1943) it comprises a much less homogeneous group of strains than 

 Str. salivarius. It does not usually grow at 45° C, it forms good a-haemolytic colonies 

 on blood agar, it does not produce so low an acidity in glucose broth as Str. salivarius, 

 it often fails to clot milk, it synthesizes no polysaccharide from sucrose or raffinose, it 

 does not form mucoid colonies on 5 per cent, sucrose agar, it usually ferments lactose 

 and sahcin but not as a rule raffinose or inuhn, and it fails to hydrolyse sodium hippurate 

 or, with some exceptions, sesculin. 



Str. equinus. — This organism is found in the intestine of the horse. It is said to grow 

 at 45° C, to produce good greening on blood agar, to produce no polysaccharide from 

 sucrose or raffinose, to hydrolyse sescuUn but not hippurate, to grow on blood agar con- 

 taining 30 per cent. bUe, and to ferment sahcin but not lactose. It is usually reported 

 as fermenting raffinose, but Sherman, Niven and Smiley (1943) disagree with this statement. 



Str. bovis. — This organism has already been mentioned under Group D hsemolytic 

 streptococci and on p. 588. 



Str. acidominimus. — This organism was described by Ayers and Mudge (1922), who 

 isolated it from cows' milk and faeces. It is also found in the vagma of the cow (Smith 

 and Sherman 1939). It forms a-haemolytic colonies on blood agar, it fails to grow at 

 10° C. or 45° C, it has very weak fermentative properties producing a final pH in glucose 

 broth of about 6-2, it has some hydrolysing effect on hippurate but not usuaUy on sescuhn, 

 it ferments lactose and sucrose, and sometimes mannitol, but not as a rule sahcin or 

 raffinose, it has httle or no action on htmus milk, and in milk containing 1 : 10,000 methylene 

 blue it fails to grow. 



Str. thermophilus. — This organism produces completely non-haemolytic colonies on 

 blood agar, but may conveniently be mentioned here. It was described by Orla-Jensen 

 (1919) as one of the organisms that grows actively in milk at a temperature of 50° C. 

 It does not grow at 10° C, it is not destroyed by heating to 63° C. for 30 minutes, it forms 

 long chains in milk, its colonies are of the pin-point type, it ferments lactose and sucrose, 

 but not sahcin, and it clots milk but has only shght reducing action on the htmus. Whether 

 disaccharides are fermented by this organism without prehminary hydrolysis to mono- 

 saccharides has been discussed by Wright (1936) and Sherman and Stark (1938). 



Omitting Str. thermophilus, which is non-haemolytic, we feel that it is wiser 

 at present to use the non-committal group term *' viridans streptococci " for 

 these organisms rather than the specific name Str. viridans. The strongest claim 

 to specific rank appears to be possessed by Str. salivarus ; and if the findings of 

 Sherman and his colleagues are confirmed, namely that all strains of this species 

 form a soluble polysaccharide from sucrose, it may be well to admit this claim. 

 The other named organisms, however, are the object of so many discrepant reports 

 that any attempt to accord them specific rank would in our opinion be premature. 



