Catalase P galactosidase a variable response has been recorded between various

Catalase p galactosidase a variable response has been

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Catalase, P-galactosidase (a variable response has been recorded between various laboratories) and lysine and ornithine decarboxylase are produced, but not H2S, indole, oxidase or phenylalanine deaminase. The methyl red test is positive, but not so the Voges Proskauer reaction. Nitrates are reduced. Growth occurs in 1.5%, but not 2% (w/v) sodium chloride. The optimum growth temperature is between 20 and 30°C, which coincides with the water temperature during severe outbreaks of the disease. Blood is degraded, but not casein, DNA, elastin, gelatin, Tween 20, 40, 60 and 80 or urea. Acid is produced from fructose, galactose, glycerol, maltose, mannose and ribose, but not from adonitol, aesculin, amyg- dalin, arabinose, arbutin, cellobiose, dulcitol, erythritol, inositol, inulin, lactose, melezitose, raffinose, rhamnose, salicin, sodium malonate, sorbitol, sorbose, starch or sucrose (Waltman et ciL, 1986). The G + C ratio of the DNA is 53 mol % (Hawkee^c//., 1981). Cryptic plasmids, i.e. pCLl and pCL2 of 5.7 kb and 4.9 kb respectively, have been found in isolates o^ Edw. ictaluri (Lobb et al, 1993). However, an isolate from green knife fish differed insofar as four plasmids, of 3.1, 4.1, 5.7 and 6.0 kb, were present. Of these, the 4.1 and 5.7 kb plasmids hybridised strongly (Lobb et ai, 1993). Similarities have been observed with Edw. tarda, except that isolates of Edw. ictaluri did not produce H2S or indole, or ferment glucose with the production of gas at 37°C. Moreover, the isolates did not agglutinate with antiserum to Edw. tarda (Hawke, 1979). However, in terms of DNA relatedness, the causal agent of enteric septicaemia of catfish was determined to be most similar to Edw. tarda, i.e. 56-62% DNA homology, but sufficiently distinct to warrant separate species recognition (Hawke et al., 1981). It remains for further work to elucidate the relationship, if any, with Edwardsiella phenon 12 of Johnson et al. (1975). Edwardsiella tarda (= Paracolobactrum anguillimortiferum, Edw. anguillimortifera) Whereas Edw. ictaluri has remained confined within the broadly defined geographical limits of the U.S.A., Edw. tarda has emerged with some frequency in the Far East, particularly Japan and Taiwan (Wakabayashi and Egusa, 1973; Miyazaki and Egusa, 1976; Kou, 1981). The history of edwardsiellosis, as the disease is called, may be traced to two separate parallel developments, i.e. those of Wakabayashi and Egusa (1973) in Japan, and Meyer and Bullock (1973) in the U.S.A. The situation is further complicated by an earlier report of Hoshina (1962), who described Paracolobactrum anguillimortiferum as a pathogen of pond-cultured eels. This organism is probably synonymous with Edw. tarda. The organisms from fish match closely the description of Edw. tarda (Ewing et al., 1965; Cowan, 1974; Farmer and McWhorter, 1984), insofar as they are fairly
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Characteristics of the pathogens: Gram-negative bacteria 103 reactive (Table 4.2), Gram-negative rods, motile by means of peritrichous flagella.
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