Alteromonadaceae representative Shewanella putrefaciens It is assumed that the

Alteromonadaceae representative shewanella

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Alteromonadaceae representative Shewanella putrefaciens It is assumed that the organism was derived from the coastal marine environment. Possibly, the organism comprises part of the normal microflora offish (see Lee et al., 1977; Gillespie, 1981). Enterobacteriaceae representatives Citrobacter freundii The organism is common in eutrophic freshwater, from which spread to fish is possible (Allen et al., 1983b). In addition, the organism was widespread in the sea- water in a Japanese aquarium (Sato et al., 1982).
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Epizootiology: Gram-negative bacteria 269 Edwardsiella ictaluri The natural reservoir for infection has not yet been firmly established. It is known that the organism survives for limited periods, i.e. up to 8 days, in sterile pond water (Hawke, 1979). This suggests that Edw. ictaluri has only limited abihty to survive in the aquatic environment. A carrier state in channel catfish has been documented (Klesius, 1992). Also, data have shown that cells can pass from dead fish to non- infected channel catfish (Klesius, 1994). Of course, the results of such laboratory- based survival experiments need to be treated cautiously. It is conceivable that the organism comprises part of the normal microflora of fish, lurking perhaps in the digestive tract. Edwardsiella tarda The precise source of infection is often unknown. However, between 2002 and 2004, Edw. tarda was recovered from seawater and the kidney and spleen of healthy Japanese flounder when disease was occurring in farmed fish populations. It was apparent that the antibody titre increased rapidly in the run-up to outbreaks of cHnical disease. Interestingly, bacteriophage was found in the seawater at least one month before the onset of and during the period of the disease outbreaks, but not afterwards. It was speculated that the presence of bacteriophage could be used as an indicator for Edw. tarda cells (Matsuoka and Nakai, 2004). Also, there has been speculation that snakes or faecal contamination from humans or other animals may have been involved in the first documented outbreak (Meyer and Bullock, 1973). Certainly, experimentally infected fish (= Japanese flounder) were determined to shed the pathogen 1-6 days before death, with the number of bacterial cells shed from newly dead (and for several days afterwards) fish reaching 10^-10^ CFU/min. Of relevance, these cells were more virulent than their counterparts from TSA. Such bacteria, which are discharged from diseased/dead fish, may well have importance in the spread of disease among fish populations (Matsuoka, 2004). Environmental parameters, namely water temperature and the quantity of organic matter in the water, undoubtedly influence the severity of outbreaks. In particular, it is noteworthy that most disease outbreaks occur at high water temperature, i.e. 30°C, when high levels of organic matter are present. However, data showed that the incidence of disease in catfish ponds rarely exceeded 5%, except when infected fish were moved to holding tanks. During these periods, edwardsiellosis became rampant with total mortalities approaching 50% of the population (Meyer and Bullock, 1973).
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  • Spring '20
  • Bacteria, representative, gram-negative bacteria

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