684 STREPTOCOCCUS 



(1912) noted the absence of haemolysis on blood agar plates. Sherman and Albus (1918), in 

 a careful comparative study of strains of this organism, and of other strains referred to as 

 Str. pyogenes, noted the following points of difference. The lactic-acid streptococcus grew 

 predominantly as diplococci or short chains, it clotted milk within 24 hours, it produced 

 high acidity in milk (0-75 per cent, or more measured as lactic acid), it grew well at 10° C, 

 but very poorly at 43° C, and it rapidly reduced methylene blue, litmus, indigo carmine 

 and neutral red. In each of these characters it differed sharply from Sir. pyogenes. Ayers, 

 Johnson and Mudge ( 1924) report that the lactic-acid streptococcus produces high acidity, 

 rapidly clots and decolorizes litmus milk, and reduces methylene blue, or Janus green. 

 This particular streptococcus has for long enjoyed specific rank, under the title Str. lactis ; 

 but it will be noted that many of its most striking characteristics are shared by enterococci. 

 Ayers and Johnson ( 1924) carried out a careful comparative study of these two types, testing 

 them as regards their reaction on blood agar, their morphology, their abiUty to withstand 

 heating at 60° C, their reaction in litmus milk and Janus green medium, their fermentation 

 reactions, and the final pH attained. They were unable to detect any difference in be- 

 haviour, except that enterococci appeared to form acid somewhat less vigorously than 

 Str. lactis. Kleckner (1935) also concludes that it is not possible to differentiate with 

 certainty between lactic-acid streptococci and enterococci, though there are minor points 

 of difference. Many strains of lactic-acid streptococci, for instance, fail to ferment mannitol. 

 The origin of these streptococci in milk is an unsolved problem. It seems clear that 

 they are not normal inhabitants of the cow's udder, but find their way into the milk from 

 some outside source (Sherman and Albus 1918, Ayers, Johnson and Mudge 1924). Stark 

 and Sherman (1935) have recorded their common occurrence on certain plants. 



The relation between these three groups of streptococci has become clarified 

 as the result of recent work. In the first place it has been shown by Graham 

 and Bartley (1939), Sherman, Smiley and Niven (1940), Seelemann and Nottbohm 

 (1940), Shattock and Mattick (1943) and Ehrismann (1943) that the enterococci 

 possess the specific carbohydrate antigen of Group D hsemolytic streptococci, but 

 that the lactic streptococci do not. It would appear that the enterococci differ 

 from Group D hsemolytic streptococci only in their failure as a rule to produce 

 characteristic /J-hsemolysis in blood agar. In the second place, careful comparison 

 between strains of enterococci and of lactic streptococci has revealed differences 

 in their resistance to heat and in certain growth characters that appear to be of 

 some classificatory value. Sherman and his co-workers have been most active 

 in this field. In 1934, Sherman and Stark found that enterococci withstood 

 exposure in sterile skimmed milk to a temperature of 65° C. for 30 minutes, grew 

 vigorously at 45° C, and developed in a lactose agar medium having a pH of 

 9'6 or containing 6-5 per cent, sodium chloride, whereas lactic streptococci did 

 none of these things. 



Tests of this sort, in which the result depends on a number of difi'erent factors besides 

 the main one imder examination, are seldom satisfactory, and it is not surprising therefore 

 that the findings of subsequent workers have varied considerably. Shattock and Mattick 

 (1943) find that resistance tests are best carried out in broth at 60° C, that special pre- 

 cautions have to be taken to maintain a pH of 9-6 in lactose agar, and that growth of 

 enterococci in the presence of 6-5 per cent. NaCl is often so poor as to render this test 

 of httle value. Ehrismann (1943) finds the heat-resistance test um-eliable, some true 

 enterococci proving susceptible, and some fsecal streptococci other than those belonging 

 to Group D proving resistant. Hobbs (1939), working in our laboratory, noted a number 

 of discrepancies in the behaviour of fcecalis and lactis strains in the Sherman set of tests 

 and Ehrismann (1943) in Germany made similar observations on faecal streptococci. 

 According to Shattock (1945) the only two rehable tests are growth at 45° C. and at pH 9-6. 



