Chapter XVI 



— 187 



Sanitary Aspects 



numerical value of the greatest dilution in which E. coli is found. The 

 sum of five such values is the "score." An illustrative example follows: 



Oyster score: 



32 



The necessity of confirming the presence of E. coli with dependable 

 tests is emphasized by Perry (1939) who points out that other types of 

 coliform bacteria associated in large numbers with shellfish may have no 

 sanitary significance. He recommends the Eijkman test in which the 

 differential media are incubated at 46° C. in order to eliminate Aerogenes, 

 Citrohacter, and other coliform types of bacteria which ferment lactose. 

 Perry found that only o.i to 10 per cent of the coliform organisms in 

 oysters from Chesapeake Bay were E. coli. There was no constant rela- 

 tionship between the two groups. Oftentimes no E. coli were found in 

 100 grams of freshly shucked or market oysters in which several thousand 

 representatives of the coliform group were demonstrated. Experimental 

 results of many investigators show convincingly that E. coli is not an 

 inhabitant of normal, unpolluted oysters (Hunter and Harrison, 1928). 

 Likewise Clostridium welchii, CI. aerogenes, Aerobacter aerogenes, A. cloacae, 

 and Streptococcus faecalis are not found in normal, unpolluted oysters, 

 although oysters are often contaminated with these organisms. Addi- 

 tional data and many references are given by Tanner (1944) on the 

 significance of oysters in the dissemination of disease, the purification of 

 shellfish, microorganisms in market oysters, the bacteriological examina- 

 tion of shellfish, and other aspects of the microbiology of shellfish. 



Oysters themselves may be susceptible to bacterial diseases. The 

 death of a large number in English oyster beds in 1920 and 1921 was at- 

 tributed by some investigators to bacterial infection, but doubt is ex- 

 pressed by Eyre (1923). From diseased as well as from healthy oysters, 

 Eyre isolated two new species. Vibrio fuscus and Spirillum ostreae. He 

 also demonstrated the presence of Cladothrix dichotoma, five species of 

 Bacillus, and two micrococci, which he believed to be variants of Micro- 

 coccus cinnebareus. None of these organisms appeared to be pathogenic 

 for oysters. 



Spirochaetes ostensibly parasitic in the gut of oysters were found in 

 the digestive tract of 91 per cent of the Baltimore, Maryland, market 

 oysters examined by Dimitroff (19266). He identified Saprospira 

 grandis, S. lepta, S. puncta, Cristospira anodofttae, Cr. speculifera, Cr. modi- 

 alae, Cr. tejiua, Cr. mina, Cr. balbianii, and Spirillum ostreae. Earlier, 

 DmiTROFF (1926a) described Spirillum virginianum which he found asso- 

 ciated with oysters. Bergey ei al. (1939) report that Cristospira interro- 

 gationis and Cr. pinnae were isolated from the intestinal canal by the 

 scallop, Pecten jacobaeus. 



The spoilage of oysters takes place in three stages, according to Eliot 

 (1926). First there is a period of rapid increase in acidity due to the bac- 



