March, 1952 ] H. LAXMINARAYANA et
al
39
and non-spore forming organising and their colonies (deep or sub-surface) on agar
were small, compact and round, oval or disc shaped. Under the low power of a
microscope, the colonies of streptococci generally appeared smooth and round or
oval shaped with entire margins, while in the case of lactobacilli both smooth as
well as rough and filamentous types of colonies were encountered. Growth on agar
slants was very scanty while good growth (filiform or beaded) was observed
in a dextrose or lactose agar stab. None of the organisms was found to produce
catalase, reduce nitrate to nitrite or produce indol
Streptococci. It will be seen (Table III a and b) that the streptococci have been
divided into four distinct species viz., S. thermophilus (10 isolates); S. lactis (6
isolates); S. faecalis (10 isolates); S. liquefaciens (3 isolates) and heterofermentative
types tentatively indentified as S. faecalis (5 isolates). It was not possible to
differentiate between the streptococci on the basis of their morphology or colony
characteristics since all of them generally appeared as spherical or oval cells (0.6 to
1.0µ diameter) arranged in pairs or short chains and formed smooth colonies. Long
chains of cells and capsulated forms were conspicuously shown only by two strains
of S. thermophilus (S. 240 and S. 197) and one of S. lactis (S. 10). Significant differ-
ences were, however, observed in respect of growth at different temperatures, action
on litmus milk, production of volatile acid, acetoin formation from citrate and
production of ammonia from arginine, which were of diagnostic value in the iden-
tification of their species. With the exception of the isolates included under S.
liquefaciens and heterofermentative members of S. faecalis groups, there was no
appreciable production of volatile acidity in milk. None of the streptococci studied
gave evidence of gas formation either in milk, in sugar broths or in semi-solid glucose
agar media. All of them fermented dextrose (except for two isolates of S. ther-
mophilus) and lactose but in regard to fermentation of other sugars considerable
variations were encountered even in the case of organisms included in the same
species.
The organisms identified as S. thermophilus were all characterised by their ability
to grow at 50°C., failure to grow at 10°C., resistance to pasteurisation (63°C. for
30 minutes), rapid acid production and coagulation of milk without reduction of
litmus, inability to produce acetoin from citrate or ammonia from arginine
and poor tolerance to high pH, NaCl and methylene blue. The time
of coagulation of plain milk at 37°C. ranged from 6 to 24 hours and the organisms
were able to curdle yeast dextrose milk in 4 to 6 hours at 45 to 47°C. A firm curd
with very little whey separation and a mildly acidic flavour was formed. The
maximum acidity produced varied from 0.8 to 1.0 per cent lactic acid. Most of
them fermented sucrose but not maltose and dextrin. Three islolates (S. 240, S. 258
and S. 252A) may be considered to be most typical of the species, although S. 252A
fermented maltose. Two of them (S. 240 and S. 258) fermented dextrose very weakly;
in course of time they were found to have completely lost their ability to ferment
this sugar, while their capacity to produce acid from lactose and sucrose remained
unaltered. The occurrence of a number of isolates in the S. thermophilus group,
showing a similar inability to ferment dextrose, has been indicated in the preliminary
classification of the organisms. This anamolous metabolic behaviour of some