|Abstract or Summary
- In an attempt to determine the natural habitat of Streptococcus
lactis, Streptococcus cremoris, and Streptococcus diacetilactis 27
different species of vegetables, 18 species of fruits and many individual
cow raw milk samples were examined.
S. lactis was found to occur on potatoes, corn, cucumbers,
peas, beans, and cantaloupe. In each case the organism was isolated
in low numbers. The remaining 21 vegetables failed to yield
any of the organisms sought.
No lactic streptococci were isolated from any of the fruits
examined. Almost all of the organisms isolated from fruits were
able to grow at 45°C., thus precluding their identification as lactic
streptococci. Those which did not grow at 45°C. had a cell morphology
which excluded them from the lactic streptococcus group.
Individual cow milk samples provided S. lactis, S. cremoris,
and S. diacetilactis isolates. If the milk samples were kept at 21° C.
for two to three days before plating, good yields of streptococci could be obtained, especially S. lactis. However, if the milk samples
were immediately plated upon receiving them, lower numbers
The biochemical, cultural, and morphological characteristics
of both the plant and milk isolates agreed in every detail with the
standard descriptions of the lactic streptococci available in the
recent literature; growth was found to take place at 10°C. and at
40°C, but not at 45°C. Litmus milk was acidified and completely
reduced before curdling. No gas production was observed in the
Acid producing abilities of those cultures isolated from plants
were somewhat higher than those cultures isolated from milk. Also,
there was a wider range in acid producing abilities of the milk isolates
than those cultures obtained from plant material.
Most of the cultures which were isolated from plants produced
concentrations of less than 50 ppm of total carbonyl compounds expressed
as pyruvic acid. This also was true for those cultures obtained
from milk. However a wide range (16 to 76 ppm) in the ability
to produce carbonyl compounds was seen in both cases.
The isolation of S. lactis from several different plant sources
confirmed the belief that plants are the natural habitat for this bacterium.
Failure to isolate S. cremoris from plant material suggests
that this species may be a variant of S. lactis with milk as its natural