March 1952 ] H. LAXMINARAYANA et al.
29
The identification of streptococci also has been somewhat confused particularly
in the distinction between S. lactis and S. cremoris and between S. lactis and S.
faecalis. S. cremoris was for a long time considered to be a variant of S. lactis but
on the basis of the differences in their maximum growth temperatures, their tolerance
of alkali and salt in the medium, their inhibition by methylene blue and their capacity
to produce ammonia from peptone, they are now generally accepted as two distinct
species [Yawger and Sherman, 1937]. Davis [1935, b] has drawn attention to the
differences between the two species in respect of morphology, inhibition by lactate,
and fermentation of maltose, dextrin, arabinose and mannite, most of which have
been confirmed by Hunter [1946]. Shattock and Mattick [1943] found a close
serological relationship between the two species although their phage reactions were
different. Similarly, S. faecalis has been differentiated from S. lactis on the basis
of its higher heat resistance as well as alkali and salt tolerance [Sherman and Stark,
1934]. Sherman et al. [1940] found S. lactis and S. faecalis to be serologically distinct,
while Gunsalus et al. [1944] reported that S. lactis was a variant of S. faecalis.
Sherman [1937] in his critical review of the literature on the taxonomy of strep-
tococci pointed out certain significant differences in the cultural and physiological
properties of these organisms which could be utilised for diagnostic purposes.
The heterofermentative streptococci (genus leuconostoc) and the streptococci
commonly employed in butter cultures have been reviewed by Hucker and Pederson
[1930] and by Hammer and Babel [1943]. The Enterococci and related streptococci
were studied by Sherman [1938]. In the classification of enterococci as well as their
differentiation from lactic streptococci both physiological and serological reactions
have been employed [Sherman, 1938; Graham and Bartley, 1939; Shattock and
Mattick, 1943 ; Shattock, 1945; Evans and Chinn, 1947]. Bacteriophage specificity
is another criterion that has been used for the differentiation of S. lactis, S. cremoris
and S. faecalis [Shattock and Mattick, 1943 ; Hunter, 1946], but this test would
appear to hold promise only for those species for which the specific phages have
been isolated. It is also known that the bacteriophages are highly influenced by
strain variations and other factors. Among the other characteristics, which have
been used for distinguishing the different species of streptococci, may be mentioned
the following : behaviour towards various oxidation-reduction indicators [Davis,
1938]; influence of pH [Davis and Thiel, 1939]; utilisation of lactate and citrate
as sources of carbon [Foster et al., 1942 ; Campbel and Gunsalus, 1944]; production
of ammonia from arginine [Niven et al., 1942] and production of carbon dioxide
from glucose [Gibson and Abd-El-Malek, 1945]. Exceptional strains of S. thermo-
philus, S. bovis and other species which gave variable results in respect of some
of the above tests have been reported by Various workers [Wright, 1936 ; Nichols,
1939; Nichols and Hoyle, 1948]. In a recent study of the streptococci of milk,
Abd-El-Malck and Gibson [1948] have outlined the most typical taxonomic character-
istics of the different groups of streptococci.
Davis and Rogers [1939 a and b] grouped different species of streptococci and
Lactobacilli on the basis of their metabolic activities and later Davis [1940] outlined
a broad scheme for simplifying the classification of the organisms on the above
basis. Kitahara [1940] suggested a new classification of lactic acid bacteria based
on morphology, sugar fermentations and other properties. In the Sixth Edition of
Bergey's Manual [Breed, Murray and Hitchens, 1948] an attempt has been made
6 A