ZoBell 



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Marine Microbiology 



practically all of the American epidemics which have been traced to shell- 

 fish, it was demonstrated that the oysters which caused the outbreak had 

 been 'iloated' or 'fattened' in brackish water near the mouths of polluted 

 streams." Rigorous control measures have done much to lessen the inci- 

 dence of shellfish-borne diseases during the last two or three decades. 



The control of the sanitary conditions under which shellfish are raised 

 and handled is a constant problem for health officials. Although typhoid 

 fever is the disease most often discussed in this connection, such diseases 

 as cholera, diarrhoea, and gastroenteritis also may be transmitted by 

 shellfish (Tanner, 1944). Botulism from shellfish is of very rare occur- 

 rence. Obviously oysters that have been grown or floated in polluted 

 water are undesirable as articles of human food, regardless of whether 

 or not they contain specific organisms of disease. Several instances of 

 the demonstration of typhoid bacilli in shellfish are related by Hunter 

 and Harrison (1928). These workers record evidence for the survival 

 of typhoid bacilli in oysters for from 9 to 42 days and of Escherichia coli 

 for from 7 to 17 days. Shellfish poisoning is discussed on page 199. 



DoDGSON (1928) gives experimental evidence that Eherthella iyphosa 

 survived in oysters, mussels, and other shellfish in sea water for more than 

 three weeks. He cites several epidemiological instances of the prolonged 

 survival of virulent typhoid bacilli in mussels and oysters. 



Large numbers of saprophytic bacteria are ordinarily associated with 

 oysters. These are considered of little sanitary significance except that 

 they promote the decomposition of shellfish. This can be retarded by 

 proper refrigeration, although some marine bacteria slowly multiply at low 

 temperatures. Tanikawa (1937) reported the slow multiplication of 

 bacteria in oysters at 0° C. There was little or no multiplication at 

 — 5° C, as shown by the data in Table XXXIX. 



Table XXXIX. — Bacterial populations of oyster meats after (liferent periods of storage 

 at diferent temperatures (from Tanikawa, 1937): — 



Tonney and White (1926) noted a 458 per cent increase in the Es- 

 cherichia coli content of shucked oysters held for 12 days at 5.8° C. In 

 another lot of oysters the E. coli score increased 1490 per cent in 11 days 

 at 5.8° C. The E. coli content of living oysters did not decrease from the 

 eleventh to the 23rd day when stored at 5.8° C. After the 28th day a con- 

 sistent decrease was noted, and after the 60th day the E. coli tests were 

 negative. 



The Committee on Standard Methods for the Examination of Shell- 

 fish of the American Public Health Association has outlined methods for 

 collecting, handling, transporting, and examining oysters for their E. coli 

 content. Oyster meats are scored by determining the highest dilution, in- 

 creasing by powers of 10, in which the presence of E. coli is confirmed by 

 the use of appropriate differential media. The results are recorded as the 



