May 15, 1925 
Microorganisms in Decomposing Oysters 
975 
It is well known that oysters con¬ 
tain carbohydrate in the form of 
glycogen. Very few of the organisms 
isolated and studied in this investiga¬ 
tion were able to attack pure glycogen. 
A great many of them, however, were 
able to ferment dextrose, maltose, or 
both. Mitchell ( 9 ) stated that, with 
approaching death, glycogenolysis takes 
place in the dying animal tissue, making 
dextrose and maltose available. In the 
investigation here reported, tests were 
conducted to demonstrate the presence 
of reducing sugar in freshly shucked 
oysters. The fermenting or souring of 
oysters, therefore, is due to fermenta¬ 
tion of the available dextrose and mal¬ 
tose rather than to direct decomposi¬ 
tion of glycogen. 
The results of this study indicate 
that the decomposition of shucked 
oysters in the beginning is probably 
due primarily to the activities of some 
members of the Serratia, Pseudomonas, 
Proteus, Clostridium, Bacillus, Aero- 
bacter, and Escherichia groups of 
bacteria. Later in the course of the 
spoilage, streptococci, lactobacilli, and 
yeasts find more suitable conditions 
for development, until in the very late 
stages of decomposition the high-dilu¬ 
tion plates made from the oysters, 
which become very sour and putrid, 
contain almost exclusively colonies of 
these three groups of organisms. In 
such oysters the hydrogen-ion concen¬ 
tration is between Ph 5.0 and 4.6. 
Washing the shucked oysters in 
fresh water or in brine as conducted in 
these experiments had no apparent 
effect on the character of the bacterial 
flora causing spoilage. The oysters 
employed in these experiments were 
divided into two lots. The shells of 
the oysters in one lot were scrubbed 
thoroughly with a stiff brush under 
running water. The shells of the other 
lot were left unwashed. The oysters 
in both lots were then shucked in their 
own liquor. The oysters of one batch 
from washed shells and of one batch 
from unwashed shells were drained, 
washed in a colander in running fresh 
water for a few minutes, allowed to 
stand in a pan of fresh water for 10 
minutes, drained, and stored. The 
remaining batch from each lot of shell 
oysters was drained, washed in a col¬ 
ander in running fresh water for a few 
minutes, allowed to stand in a pan of 
2.5 per cent salt solution for 10 minutes, 
drained, and stored. The organisms 
which were found responsible for the 
decomposition were isolated consistent¬ 
ly from the washed as well as the un¬ 
washed oysters. In commercial prac¬ 
tice the use of a “blower” might, in 
some slight degree, affect the character 
of the flora, although various investi¬ 
gators have reported the impossibility 
of removing bacteria from the digestive 
canal of the oyster by any method of 
washing. Regardless of the effect of 
washing on the bacterial flora, good 
commercial practice calls for a thor¬ 
ough washing of shucked oysters in a 
weak brine to remove dirt, pieces of 
shell, seaweed, and other foreign mate¬ 
rial, and to produce as clean a product 
as possible. 
SUMMARY 
The decomposition of shucked oys¬ 
ters is apparently due primarily to the 
presence and development of certain 
members of the following groups of 
bacteria: Serratia (water and soil bac¬ 
teria producing red pigment), Pseudo¬ 
monas (the fluorescent group), Proteus, 
Clostridium (the anaerobic spore-form¬ 
ing group), Bacillus (the aerobic spore¬ 
forming group), Escherichia (the colon 
bacteria), Aerobacter (the aerogenes 
group), Streptococcus, and Lactoba¬ 
cillus. Some decomposition is also 
caused by certain yeasts. 
The streptococci, lactobacilli, and 
yeasts predominate in the late stages 
of spoilage, when the hydrogen-ion con¬ 
centration is between P H 5.0 and 
Ph 4.6, while the other forms predom¬ 
inate in the early stages of decomposi¬ 
tion. 
The remaining organisms, compris¬ 
ing the microflora of oysters, are, for 
the most part, ordinary nonspore¬ 
forming soil and water bacteria and 
yeasts. 
LITERATURE CITED 
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