May 15, 1925 
Microorganisms in Decomposing Oysters 
973 
Table I.— Organisms producing foul odors in oysters and oyster infusion medium 
CnlturP Number 
S of times 
isolated* 
Stage of spoilage when isolated 
Species resembled 
8c_ 29 
4G_ 17 
Present throughout whole period of spoil¬ 
age. 
_do_ _ 
Serratia sp. (Bizio). 
Pseudomonas fluorescens (Fliigge). 
Proteus vulgaris (Hauser). 
Bacillus cereus (Frankland). 
Clostridium sp. (Prazmowski). 
Do. 
Do. 
Do. 
Bacillus subtilis (Ehrenberg) Cohn. 
Bacillus aterrimus (Lehmann and 
Neumann). 
Bacillus simplex (Gottheil). 
Bacillus prausnitzii (Trevisan). 
2C___. 27 
_do._ __ __ 
IP.. 6 
_do.. .. 
3AN_| 20 
_do_ _ ___ 
5Ai_ 24 
_do _ _ _ 
5A*_ 15 
_do_ _ _ _ 
6Ai__. 8 
..do.. _ ___ 
IF_ 1 8 
9G__. 2 
Present during early stages of spoilage_ 
_do_____ _ 
7 ..; 11 
_do_ 
12A_ 2 
_do. ____ _ 
' I ‘ 
° In picking colonies from plates an effort was made to pick all the representative colonies from every 
plate examined. 
There is no fermentation of dextrose, 
lactose, sucrose, or maltose. Indole 
is not produced. Nitrates are reduced 
to nitrites. Hydrogen sulphide is 
produced. 
Four spore-forming obligate anae¬ 
robes were isolated in the course of the 
investigation. These organisms re¬ 
sembled one another closely, but were 
carried through the investigation as 
individual organisms. It has not been 
possible to identify these anaerobic 
bacteria as to species, but it has been 
determined that they are active agents 
in producing spoilage in oysters. 
Although decomposing shucked oys¬ 
ters have a foul and putrefactive odor, 
their predominating odor and their 
appearance are such that they are 
usually referred to as ‘‘sour” oysters. 
In Table II are listed the organisms 
which produce this sour odor or produce 
acidity as indicated by the hydrogen- 
ion concentration. 
All the organisms in Table II, in 
pure-culture inoculation of oysters and 
oyster infusion medium, produced hy¬ 
drogen-ion concentrations varying from 
Ph 5.6 to Ph 4.4. Aerobacter aerogenes 
(Bact. aerogenes) and A . cloacae (Bad. 
cloacae) were present throughout the 
whole period of the spoilage. In pure 
culture these organisms produced not 
only a sour odor and an increase in 
acidity but also a foul and somewhat 
putrefactive odor. Escherichia coli 
(Bact. coli ) and E. communior (Bad. 
communior ) were isolated only during 
the early stages of spoilage. In pure- 
culture inoculation experiments these 
organisms produced results very similar 
to those produced by A. aerogenes and 
A. cloacae. 
During the late stages of spoilage 
the organisms predominating in the 
spoiled oysters are streptococci, lacto- 
bacilli, and yeasts. In pure-culture 
inoculations the streptococci produce 
Table II.— Organisms producing acidity , sour odor , or both, in oysters and oyster 
inf usion medium 
Culture 
(CS) 
7L__. 
2N_ _ 
10E. 
14E. 
20E. 
7A20- 
10Q. 
13A 3 . 
20c__ 
16P_. 
16S_. 
17A. 
1Z... 
NY*. 
20A*. 
Number 
of times 
isolated 
Stage of spoilage when isolated 
Type resembled 
71 
Present throughout whole period of spoil¬ 
age 
Aerobacter aerogenes (Escherich). 
21 
Aerobacter cloacae (Jordan). 
21 
Present during early stages of spoilage_ 
■ Escherichia coli (Escherich). 
13 
_do_ 
Escherichia communior (Durham). 
16 
Present during late stages of spoilage_ 
Lactobacillus sp. (Beijerinck). 
2 
-do_ 
Streptococcus sp. (Bosenbach). 
25 
_do_ 
Streptococcus lactis (Lister). 
1 
Present during early stages of spoilage_ 
Bacillus mycoides (Fliigge). 
5 
Abundant during late stages of spoilage_ 
Yeasts. 
5 
-do_ 
Do. 
4 
_do_ 
Do. 
4 
_do_ 
Do. 
4 
_do_ 
Do. 
1 
Isolated during late stages of spoilage_ 
Do. 
2 
1 
_do_ 
Yeastlike fungus. 
