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On agar-agar.—Streak cultures at 20° C. show distinct growth in two days, semi-transparent
and barely pink. At the end of a week the growth is opaque and of a bright pink colour, the
streak being some 3 m.m. wide. At 37° C. no growth occurs.
On potato.—Grows exceedingly well, forming a thick layer of a brilliant deep pink colour,
which eventually covers the whole surface.
In broth.—The fluid gradually becomes turbid, and after a week there is a light pink sediment
at the bottom of the tube.
Temperature.—Grows well at 20° to 22° C. No growth on any medium at 37° C.
Rapidity of growth.—Grows rather slowly, but maximum of growth is attained in 7 to 10 day?.
Spore formation.—Not observed.
Need of oxygen.—Growth very scanty away from the surface.
Gas production.—Not observed.
Action on gelatine.— Very slow and gradual liquefaction after two to three weeks.
Pigment production.—Produces a bright pink pigment, readily soluble in alcohol, only slightly
30 in water.
Relations.—Appears most closely related to Micrococcus agilis and Micrococcus roseus, but differs
from the former in the absence of motility and the lighter pink colour of the cultures, and from the
latter in the absence of any growth at 37° C.
Proteus cloacinus.
Source.—Found in every sample we have examined.
Form and arrangement.—A short bacillus of variable length: 0.4 to 0.5 µ in breadth; stained
specimens from a two-days-old agar-agar culture vary from 0.5 to 1 µ in length; the shorter forms
almost resembling cocci. On gelatine some longer forms are seen, up to 1.6 µ in length, and these may
be as much as 0.6 µ in breadth. In a one-day-old broth culture the average length is 0.8 µ.
Motility.—Actively motile.
Growth on gelatine plates.—The colonies are visible to the naked eye in 19 hours, though still
very minute. Under the microscope the surface colonies are thin, transparent and irregular in outline,
the deeper colonies globular and brownish by transmitted light. In two days the surface colonies are
more circular and regular in outline; the largest are about 1 m.m. in diameter; a few show a thin
spreading edge, but no "swarming islands" are given off. No further change occurs except that the
colonies increase in size up to 2 m.m. in diameter, and become raised at the edges; they are of a
greyish white colour. No liquefaction occurs even at the end of a fortnight. The plates have a
somewhat sour smell.
Gelatine streak cidtures.—Growth is rapid—the streak attaining a width of 1.5 m.m. in
24 hours, when it is semi-transparent and whitish, with a gummy appearance. The edges are
irregular, but show none of the characteristic "swarms" given off by Proteus vulgaris. In two days
typical streaks are white and semi-opaque with a waxy lustre, and in five days the width of the streak
may be 3 to 5 m.m. Later the growth becomes distinctly terraced, and liquefaction eventually occurs
in about three weeks. The species is, however, very variable in its behaviour in gelatine streak
culture. Specimens, the purity of which was assured by subsequent plate culture, occasionally liquefied
the gelatine in from three to five days, and in these cases "swarming islands" were thrown out from
the edges of the streak as in the common Proteus. The "swarms" are thrown out into the depth of
the gelatine as well as laterally, and the process seems associated with early liquefaction. In other
cases streaks grew with much lateral expansion, forming an irregular semi-transparent growth on the
surface like that of B. coli communis.
Gelatine stab cultures.—Growth is rapid and well marked all along the needle track. Scanty
gas bubbles are formed. Liquefaction first commences in from two to three weeks. The growth is
white and nodular in the depth.
Gelatine shake c idtures.—There is a profuse formation of gas bubbles in 24 hours; these are
later partially re-absorbed.
Agar-agar.—Agar-agar plates incubated at 37° show exceedingly rapid and characteristic
growth. A single colony spreads in 36 hours, as a thin irregular dendritic film covering almost the
whole surface of the plate. The film does not thicken on further incubation.
Agar-agar streak cidtures.—Growth is very rapid both at 37° C and 20° C. Even at the latter
temperature the whole surface of the tube is covered in 24 hours by a thin homogeneous semi-translucent
greyish film, advancing at the edge by irregular processes. On the second day the growth is
somewhat thicker and whiter and has reached its full development. There is a scanty development of
gas bubbles in the depth of the agar-agar, but no odour of putrefaction is ever perceptible.
Potato.—Grows rapidly, forming a slimy layer of a yellowish grey colour. The bacilli grow to
longer threads than on other media, and become irregularly swollen.
Broth.—In 24 hours the broth is turbid, and in a few days a slight film is present on the surface,
and a yellowish white deposit at the bottom of the tube. In a week there is a marked putrefactive
odour (absent in gelatine and agar-agar cultures). Tested, after 11 days, with nitric acid—containing
nitrous acid—no trace of indol reaction was obtained.
Milk.— Grows without producing any change in this medium.
Temperature.—Grows equally well at 37° C and 20° C.
Rapidity of growth.—Grows very rapidly, and on agar-agar with extraordinary quickness.
Spore formation.—Not observed.
Need of oxygen.—Grows well in the depth in stab cultures.
Gas production.—Abundant.
Action on gelatine.—Variable. Typically, no liquefaction occurs till after a lapse of two or three
weeks; exceptionally, it occurs in three to five days.