| Resumo: |
Of the several bacterial diseases which may result from consumption of shellfish, those caused by marine bacteria of the genus Vibrio are the most abundant. In the United States, up to 10,000 non-fatal cases per year are estimated to be caused by the various members of this genus. More than 95% of all deaths in the United States which result from seafood consumption are caused by a single bacterium, Vibrio vulnificus. The bacterium is a normal inhabitant of estuarine waters, and occurs naturally in especially high numbers in molluscan shellfish. Infections following consuption of raw or undercooked shellfish, especially oysters, result in fatality rates of over 60%. Because most oysters in the United States are transported large distances before marketing, the possibility of temperature abuse of oysters as a factor in the epidemiology of this disease was investigated. Oysters (Crassostrea virginica) were allowed to take up cells of . vulnificus (CVD713) which had been added with algal cells. Following uptake, the live, shellstock oysters were placed at temperatures of 0.5, 5, 10, 17 and 22 degree C and maintained at those temperature for up to 10 days. At intervals, groups of five oysters were removed and assayed for the number of V. vulnificus cells present. Strain CVD713 contains the transposon, which carries genes for kanamycin resistance and alkaline phosphatase production. These markers permit significant selectivity of this strain from other normal flora bacteria, as well as differentiation from other kanamycin resistant cells that may be present. Temperature studies demonstrated that the transposon was stable at all investigation temperatures (Figure 1). Results indicated that, regardless of storage temperature, the number of V. vulnificus cells present in shellstock oysters decreased gradually with time, with the greatest decreases occurring at the higher temperatures (Figure 2). A similar result was seen when a 1000-fold lower number of cells were initially present in the oysters (Figure 4). No significant differences in cell survival were noted between opaque (encapsulated) cells (Figure 2) and translucent (non encapsulated) cells (Figure 6) of V. vulnificus. Similar results were obtained when an identical study was carried out employing a strain of V. cholerae harboring this transposon (data not shown). In contrast to the results observed when the storage studies were conducted on shellstock oysters, a rapid and dramatic decrease inV. vulnificus cell survival was observed at all temperatures when oysters were shucked prior to storage (Figure 7). Our results suggest that temperature abuse may not be a major factor in the epidemiology of infections by V. vulnificus. However, storage of V. vulnificus at low temperatures does not appear to significantly reduce the populations of this human pathogen.
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