38 STUDIES ON DAHI. III. TAXONOMY OF THE LACTIC ACID, ETC. [Vol. XXlI, Part I
The isolates-in L. casei group (Streptobacteria) appeared as short and thin rods
occurring in pairs or short chains and showing granules occasionally. They showed
growth at 10°C. and a few isolates grew at 45°C. also. Nearly 50 per cent of them
were able to coagulate milk in 2 to 3 days at 37°C. while the rest took 10 to 14 days.
Litmus was partially reduced and both maltose and sucrose were generally
fermented.
The remaining lactobacilli, which were characteristically slow acid producers
have been included in L. brevis group. They generally resembled the isolates in
L. casei group in their morphology. With the exception of a few organisms they
did not grow at 45°C. but showed slow growth at 10°C. All the organisms fermented
dextrose, lactose, sucrose and maltose. Half of them produced only slight acid
in milk even after a month but in presence of yeast extract milk was observed to
coagulate in 3 to 6 days. Slight gas production was observed in milk cultures of some
of these isolates. The remaining 50 per cent of the isolates in this group were able
to coagulate milk in 3 to 10 days and also showed high aroma and acetoin formation.
The lactobacilli in L. bulgaricus group, particularly those included in sub-groups
A and B of this group were found to occur in dahi produced in almost all parts of
the country and these also formed the predominant flora of south Indian dahi samples.
The organisms in L. casei group were found to be the predominant types of lacto-
bacilli, occurring in north Indian samples of dahi, while the heterofermentative
types included in L. brevis group were found mostly in good samples of dahi obtained
from Calcutta, Darbhanga (Bihar) and Mathura (Uttar Pradesh).
Thus, almost all the types of lactic acid bacteria, reported to be present in
fermented milks [Corminboeuf, 1933; Tanner, 1944] were observed to occur in
dahi. The heterofermentative streptococci described under S. dextranicum, group-
IV, did not show any evidence of their ability to produce gas either in milk or in
dextrose broth cultures in subsequent experiments. They also became more vigo-
rous acid producers on repeated sub-culturing. These astrains were accordingly
considered to be heterofermentative variants of the organisms in S. faecalis group.
Similarly, in the case of the heterofermentative types of lactobacilli included under
L. brevis, group III only 12 isolates gave evidence of gas formation. The rest of the
organisms were, therefore, considered to be heterofermentative variants of the
organisms in Group II.
Detailed examination of selected isolates and their identification
The results of detailed taxonomical studies on selected isolates (32 streptococci
and 21 lactobacilli) are presented in Tables III (a and b) and IV (a and b). The
organisms have been grouped according to the species with which they have been
identified on the basis of their typical morphological, cultural and biochemical
characteristics (vide Table I). Photomicrographs of some of the organisms are
shown in Plates I, II and III.
Certain common characteristics, associated with lactic acid bacteria as a group
were observed for all the organisms. They were all Gram positive, non-motile