972 
Journal of Agricultural Research 
Vol. XXX, No. 10 
Several experiments were conducted 
to investigate the power of the various 
pure cultures to produce typical spoil¬ 
age in raw shucked oysters. 
Clean oysters in the shell, ob¬ 
tained from unpolluted sources, were 
“floated” in the laboratory in tanks of 
artificial sea water to which had been 
added calcium hypochlorite in sufficient 
quantity to produce 6 parts of free 
chlorine per 1,000,000 parts of water. 
Following the directions given by 
Wells (13) for artificial purification of 
oysters, an attempt was made on a 
laboratory scale to reduce the bacterial 
content of the oysters to a minimum. 
After a suitable period in the chlori¬ 
nated water, the oysters were opened 
aseptically, and one or two oysters, 
with their liquor, were placed in each 
of a sufficient number of large sterile 
test tubes. These chlorinated oysters 
were then inoculated with saline sus¬ 
pensions of the various pure cultures in 
the collection, grown for 48 hours on 
dextrose-agar slants. The inoculated 
oysters were held at 20° to 25° C., and 
daily records were made of their odor, 
appearance, and hydrogen-ion concen¬ 
tration. This experiment was repeated 
several times. Although not entirely 
successful, it furnished data which, 
when considered with some supple¬ 
mental results from another experi¬ 
ment, presumptively identified those 
organisms in the collection which were 
responsible for the spoilage of shucked 
oysters. 
In order to confirm the results ob¬ 
tained in these inoculation experi¬ 
ments, an oyster-infusion broth was 
prepared from chopped oysters, tubed, 
and sterilized in the autoclave. Before 
sterilization a small piece of oyster 
meat was added to each tube of plain 
oyster infusion. These tubes were 
inoculated with the various pure cul¬ 
tures, and the same series of observa¬ 
tions made in the inoculation experi¬ 
ments were recorded. 
EXPERIMENTAL RESULTS 
From the combined results of these 
several experiments, it was apparent 
that certain of the bacteria used 
produced foul, putrefactive odors in 
the oysters, some produced acidity or 
sour odors, and others apparently 
produced neither putrefaction nor sour¬ 
ing in pure culture, although they 
grew readily. 
Table I gives the types of bacteria 
isolated from decomposing oysters 
which, when inoculated into artifi¬ 
cially purified oysters or into oyster 
infusion medium, produced foul and 
putrefactive odors. Table II shows 
the types of organisms from oysters 
which produced acidity or sourness in 
oysters and in oyster infusion medium. 
Table III includes the remaining 
organisms isolated from decomposing 
oysters which apparently had no effect 
in pure culture. 
The data in Table I show that the 
bacteria producing foul odors in de¬ 
composing oysters are members of the 
genera 4 Serratia (water and soil bac¬ 
teria producing red pigment), Pseu¬ 
domonas (soil and water bacteria 
producing a blue-green pigment), Pro¬ 
teus, Clostridium (spore-forming obli¬ 
gate anaerobes), and Bacillus (aerobic 
spore-forming bacteria). The first four 
groups were always present during the 
course of the spoilage and were alwa}^s 
comparatively abundant and active. 
The spore-forming aerobic bacteria 
were always obtained during the early 
stages of the decomposition, and they 
did not appear to be as abundant or 
as active in producing evidences of 
spoilage as were the other organisms 
named in Table I. 
The organism designated in Table 
I as CS-8c, which evidently belongs to 
the genus Serratia, has been isolated 
repeatedly, not only in this investi¬ 
gation but in an investigation on the 
decomposition of salmon ( 5 ). Since 
this organism appears to be a particu¬ 
larly active agent in the decomposition 
of fish and shellfish and since it can not 
be identified as any member of the 
genus Serratia described in the litera¬ 
ture available, its morphology and 
cultural reactions may properly be 
given here. This organism is a Gram 
negative motile rod with bipolar 
flagella, 1.8 to 3 microns long and 
about 1 micron wide. Gelatin colonies 
are small, white, and perfectly round. 
Agar colonies are round, of medium 
size, and yellowish in the center, with 
bluish edges. Gelatin is rapidly lique¬ 
fied, the growth being mostly on the 
surface of the stab. On agar slants the 
organism grows along the streak; it is 
pinkish, moist, and slightly raised. 
There is turbidity in plain broth, with a 
very slight scum and very little sediment 
in 48 hours. In old broth cultures 
there is a heavy viscous sediment, with 
a definite ring around the tube at the 
surface of the broth. Litmus milk is 
reduced and slowly peptonized, with 
the evolution of a foul odor. On 
potato the growth is heavy, moist, 
glistening, brick red, and slightly raised. 
4 Nomenclature follows Bergey’s Manual ill). 
