46 STUDIES ON DAHI III. TAXONOMY OF THE LACTIC ACID, ETC. [ VOL. XXII, PART I
appeared to be slightly different from L. bulgaricus as they showed many curved
and coiled forms and occasionally contained more numerous granules in the cells.
In all other respects these organisms closely resembled the L. bulgaricus strains.
Isolates L.12 and L.189, which have been identified as L. helveticus differed
from the above two species in appearing as shorter and thinner cells arranged in
pairs of palisade formation almost resembling the cells of L. casei. The colonies
formed were generally of the 'smooth' type. The organisms were inhibited by
2.5 per cent NaCl but not by 0.1 per cent methylene blue. Arabinose and maltose
were fermented while sucrose, raffinose and salicin were not attacked.
The organisms included under L. casei and L. plantarum species (Streptobac-
teria) were able to grow at 10°C. and with the exception of one isolate (L.157), at
45°C. None of them showed growth at 50°C. Resistance to pasteurisation (63°C.
for 30 min.) was, however, variable. They produced acid in milk more slowly than
the Thermobacteria and took 3 to 4 days or longer to coagulate milk at 37°C.
Maximum acidity produced was 1.4 to 1.6 per cent lactic acid in the case of L. casei
strains and less than one per cent in others. They did not show any gas formation
from glucose and with the exception of two isolates (L.89 and L.73) they did not
produce any volatile acidity in milk. They were able to grow in two per cent
lactate and tolerate 2.5 per cent concentration of NaCl. All of them were inhibited
by 0.1 per cent methylene blue. In morphology, they were clearly distinguished
from L. bulgaricus and related strains by their appearance as very short and thin
rods (1.5-2.5X0.2µ) occurring in pairs, chains, palisade formation and occasionally
in long filaments. Granules were not prominent. In the case of L.157, two types
of cells—one short and thin and the other larger in size with rounded ends—were
seen. Capsulated cells were shown by the heterofermentative strains (L.89 and
L.73) in India ink preparations of the smears. The colonies formed by all these
organisms were of the 'smooth' type. All the isolates fermented arabinose, xylose,
dextrose, galactose, sucrose, maltose, lactose, trehalose and generally salicin and
mannitol.
Isolates L.401, L.401 a, L.84 and L.134, appeared to be typical strains of
L. casei from their morphology, reduction of litmus and rate of acid production,
maximum acidity produced (1.4-1.6 per cent lactic acid), sugar fermentations and
their ability to tolerate 5 per cent NaCl (except for isolates L.84 and L.134). Isolate
L.157 has been identified as L. plantarum on account of some differences shown by
the organism in respect of morphology, rate of acid production in milk (taking
5 to 7 days to coagulate milk at 37°C), inability to reduce litmus, and low maximum
acidity produced (0.5 per cent lactic acid).
Isolates L.89 and L.73 closely resembled the L. plantarum strain except for
their ability to produce high volatile acidity in milk (20-30 ml. of N/10 NaOH per
250 g. of culture). The curd formed was weak in texture but was associated with
a strong diacetyl flavour. These organisms have been considered to be hetero-
fermentative variants of L. plantarum and not included under Betabacteria in view
of their comparatively rapid rate of acid production in milk, failure to produce gas
from glucose and marked fermentation of arabinose. Similar strains of L. plantarum
do not appear to have been reported in fermented milks, although Sherwood [1939]
has referred to their occurrence in cheese and suggested the possibility of their being
intermediate forms between L. casei and L. brevis.