enabled higher production of ROS intermediates by phagocytes which suggests

Enabled higher production of ros intermediates by

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enabled higher production of ROS intermediates by phagocytes, which suggests that they are more likely to be susceptible to inactivation by this means (Rao et al., 2001). A type III secretion system has been documented (Rao et al., 2004), defective mutants having reduced virulence (Tan et al., 2005). Variable OMP patterns, including some major (25-40 kDa) and many minor proteins (~10-120kDa), have been identified in isolates when cultured at 25°C. Interestingly, saHnity affected OMP composition in some cultures, suggesting heterogeneity in the taxon (Darwish et al., 2001). Haemo- lysins and dermatotoxins, but not lipases or proteolytic enzymes, were produced in vitro, and it was postulated that these exo-enzymes may confer pathogenicity on Edw. tarda (Ullah and Arai, 1983a, b). Furthermore, the pathogenic role of dermatotoxins was highUghted in additional experiments (Ullah and Arai, 1983b). This work con- cluded that two high molecular weight, heat-sensitive dermatotoxins were produced, which in rabbits (not fish!) were found to have separate functions. Thus, one toxin caused erythema within 3-8 h of intracutaneous injection, whereas the second caused oedema followed by necrotic erythema in 5-7 days. Hopefully, at some point this work will be repeated in fish. Proteolytic toxins (molecular weight = 37 kDa), from ECP, have been purified from avirulent cultures (the toxin is not present in avirulent isolates) and the LD50 equated to 1.6 g of toxin/g offish (Suprapto et al., 1996). The organism has been associated with the development of liver hypertrophy following experimental infection of Japanese flounder (Miwa and Mano, 2000). On iron-deficient medium, many Edw. tarda cultures, notably those associated with virulence, produced siderophores (Kokubo et al., 1990; Mathew et al., 2001; Igarishi et al., 2002) and OMPs of which one was considered to be the receptor for the siderophore under iron-limited conditions. Such components permit the pathogen to scavenge for iron in the blood of the host. Certainly, it appears that the abihty of
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316 Bacterial Fish Pathogens Edw. tarda to acquire iron is an important part of the infection process (Park, 1986; lida and Wakabayashi, 1990), and it is relevant that an iron-regulated haemolysin gene has been reported (Hirono et al, 1997a). The virulent strains are more resistant to the bacteriostasis of iron-chelating reagents than their avirulent counterparts. Typical of many bacterial pathogens, Edw. tarda adheres to host cells before internahsation, which involves microfilaments and protein tyrosine kinase (Ling et ai, 2000). Using green fluorescent protein (GFP) tagged cells, the portals of entry after immersion challenge were identified as the digestive tract, i.e. anterior intestine, gills and body surface of blue gourami (Ling et al, 2001). The bacteria were located in these sites and blood, heart, kidney, liver, muscles, posterior intestine and spleen after 3 days, but declined substantially by 7 days, with only substantial populations remaining in the intestine.
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  • Spring '20
  • Bacteria, representative, gram-negative bacteria

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