42 STUDIES ON DAHI. III. TAXONOMY OF THE LACTIC ACID. ETC. [Vol. XXII, Part I,
strains of S. thermophilus deserves further investigation. Isolate S. 8 is an a typical
strain since it was able to tolerate 4 per cent NaCl and 0.1 per cent methylene blue.
Six isolates have been identified as S. lactis. They were distinguished from
S. thermophilus in their ability to grow at 10°C. and failure to grow at 45°C. or survive
(63°C. for 30 minutes, production of NH 3 from arginine (except for one isolate, S. 10)
and tolerance to pH 9.2, 4 per cent NaCl (except S. 10), and 0.1 per cent methylene
blue. They were able to coagulate milk in 14 to 24 hours at 37°C. and produced a
maximum acidity ranging from 0.75 to 0.90 per cent lactic acid. Isolate S. 157,
which fermented maltose and dextrin but not sucrose, may be considered
to be typical of the species. Two other isolates (S. 69 and S. 154) closely
resembled the typical strain except for their inability to ferment maltose and
the latter's ability to attack sucrose strongly. Isolate S. 10, which
formed a ropy curd, showed long chains of cells and capsulated forms. It
also failed to grow in 4 per cent NaCl, produce ammonia from arginine or ferment
maltose and dextrin; it thus resembled S. cremoris more closely than S.
lactis. This strain is probably similar to the organisms described by Joshi
and Ram Ayyar [1936] and Karnad [1939] except that it showed ropiness. On the
other hand, isolate S. 57 showed some relationship to S. faecalis by its ability to
tolerate pH 9.6 and 6.5 per cent NaCl.
The remaining streptococci (18 isolates) have been included in the Enterococcus
group. They were able to grow at 10°C. as well as at 45°C. and, with the exception
of 4 strains, showed growth even at 50°C. All of them survived pasteurisation
(63°C. for 30 minutes) produced ammonia from arginine and produced acid in milk
followed by reduction of litmus and coagulation of milk. With the exception of
two isolates they also produced acetoin in sugar free citrate medium and did not
show any inhibition at pH 9.6 or by 6.5 per cent NaCl and 0.1 per cent methylene
blue. Ten of these have been identified as S. faecalis. They produced acid and
coagulation of milk rapidly (8—24 hours in the case of 7 strains and 2 to 4 days in
other cases), the maximum acidity produced varying from 0.50 to 0.98 per cent
lactic acid. Isolates S. 190, S. 1, S. 30, S. 124 and S. 129 are typical of the species,
except for their variable behaviour in fermenting maltose, arabinose raffinose,
salicin, mannite and glycerol, which have been reported to be fermented by 8.
faecalis [Breed, Murray and Hitchins, 1948].
Three isolates (S. 170, S. 108 and S. 127) produced acid, reduced litmus, coagula-
ted milk rapidly (6 to 18 hours) and caused marked proteolysis of the curd. They
were, therefore, identified as S. liquefaciens. The maximum acidity produced by
them ranged from 0.55 to 0.98 per cent lactic acid. In addition to conforming to
the typical physiological reactions of the species they also produced acid from all the
important sugars (sucrose maltose, trehalose, raffinose, salicin, mannite and glycerol
reported to be fermented by S. liquefaciens [Breed, Murray and Hitchins, 1948].
Isolates S. 108 and S. 127 were found to produce appreciable amounts of volatile
acidity in milk (15.3 and 21.2 ml. of N/10 NaOH per 250 g. of culture, respectively).
Isolates S. 207, S. 209, S. 253, S. 212 and S. 213, closely resembled the previous
group, except for the fact that they produced acid in milk much more slowly (taking
3 to 4 days for coagulating milk) and did not bring about any proteolysis of the curd.
The maximum acidity produced was 0.50 to 0.60 per cent lactic acid. As they also