Edwardsiella tarda is a fish pathogen that causes systemic infections in many food and ornamental fish. E. tarda PPD130/91 and PPD125/87 were selected as representatives of the virulent and avirulent groups, respectively, from eight fish isolates, and transformed with plasmids encoding either green fluorescent protein (pGFPuv) or blue fluorescent protein (pBFP2). Two host models were used to study the invasion pathway of E. tarda in vitro and in vivo.

Enterohemorrhagic and enteropathogenic Escherichia coli (EHEC and EPEC, respectively) strains are closely related human pathogens that are responsible for food-borne epidemics in many countries. Integration host factor (IHF) and the locus of enterocyte effacement-encoded regulator (Ler) are needed for the expression of virulence genes in EHEC and EPEC, including the elicitation of actin rearrangements for attaching and effacing lesions. We applied a proteomic approach, using two-dimensional polyacrylamide gel electrophoresis in combination with matrix-assisted laser desorption ionization-time of flight mass spectrometry and a protein database search, to analyze the extracellular protein profiles of EHEC EDL933, EPEC E2348/69, and their ihf and ler mutants. Fifty-nine major protein spots from the extracellular proteomes were identified, including six proteins of unknown function. Twenty-six of them were conserved between EHEC EDL933 and EPEC E2348/69, while some of them were strain-specific proteins. Four common extracellular proteins (EspA, EspB, EspD, and Tir) were regulated by both IHF and Ler in EHEC EDL933 and EPEC E2348/69. TagA in EHEC EDL933 and EspC and EspF in EPEC E2348/69 were present in the wild-type strains but absent from their respective ler and ihf mutants, while FliC was overexpressed in the ihf mutant of EPEC E2348/69. Two dominant forms of EspB were found in EHEC EDL933 and EPEC E2348/69, but the significance of this is unknown. These results show that proteomics is a powerful platform technology for accelerating the understanding of EPEC and EHEC pathogenesis and identifying markers for laboratory diagnoses of these pathogens.Enterohemorrhagic and enteropathogenic Escherichia coli (EHEC and EPEC, respectively) strains are closely related human pathogens (7). EHEC strains, especially those of serotype O157:H7, which produce Shiga-like toxin (Stx), are a common cause of diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome, while EPEC is the most common bacterial cause of infant diarrhea (29). Both have been implicated in food-borne outbreaks in many countries and cause diarrhea by colonizing the intestinal mucosa (29, 30). EHEC and EPEC strains are distinguished from other pathogenic E. coli strains by their ability to produce a characteristic histopathological feature known as attaching and effacing (AE) lesions on the mucosa (12, 29). AE lesions are characterized by the destruction of the microvilli and the induction of actin-based pedestal formation underneath the eukaryotic membrane at the site of attachment (6). EHEC and EPEC secrete many extracellular proteins (ECPs), and the type III secretion system (TTSS) is a major secretion apparatus for secreting virulence factors which interact directly with the host (20, 25). The TTSS is located within a chromosomal pathogenicity island designated the locus of enterocyte effacement (LEE) which is necessary for the formation of AE lesions (18,19). The LEE-encoded regulator (Ler) activates most of the genes within the LEE region and is centr...

No abstract

Vibrio anguillarum and Vibrio damselee are Gram-negative bacteria that cause systemic infections called vibriosis in fish. They can enter fish cells and survive as intracellular parasites. The host-pathogen interactions between these Vibrio species and the fish epithelial cell lines epithelioma papillosum of carp (EPC) and grunt-f in tissue (GF) cells, were examined using phase-contrast, scanning electron and confocal microscopy. In addition, potential signal transduction pathways that precede bacterial internalization were studied by using signal transduction inhibitors. Some Vibrio species induced morphological changes in fish cells and this allowed classification into a cytopathic group and a noncytopathic group. The cytopathic group could be subdivided into two invasive groups (I and II) and a cytotoxic group. Of the invasive strains V. anguillarum 811218-5W (group I) and GNirus/5(3) (group II), genistein, a tyrosine kinase inhibitor, only inhibited internalization of V. anguillarum GNirus/5(3) into EPC cells, whereas staurosporine, a protein kinase C inhibitor, accelerated internalization of both strains. Cytochalasin D, an inhibitor of microfilament polymerization, prevented internalization of both strains, whilst vincristin, a microtubule inhibitor, only inhibited internalization of V. anguillarum GNirus/5(3). For the cytotoxic strain V. damselae ATCC 33539, extracellular products (ECP) alone caused morphological changes in EPC and GF. Bacterial internalization may not be important in the pathogenesis of this group. The non-cytopathic strain V. anguillarum SU5/93(2) did not enter cells or induce any changes in EPC and GF monolayen. This study has identified some major differences between Vibrio species in their interactions with fish cells in vitm and will thus facilitate future studies of the molecular basis of pathogenesis of vibriosis.

Silica sand is commonly used in the foundry industry. With a high melting point of 1600°C, the silica sand is normally sintered in a high-temperature furnace. However, silica with contents of calcium, aluminium, magnesium, and chlorine, etc. can form low-melting point eutectics. Therefore, a relatively low-power laser can be used to sinter the silica sand directly. The investigation of the mechanism and process for direct laser sintering of the silica sand, without any binder, is presented in this paper. Combined with rapid prototyping (RP) technology, the laser sintering of the silica sand can be used to directly fabricate a sand casting mould, called a rapid sand casting mould. By avoiding the time-consuming process of fabricating a pattern, the rapid sand casting mould process has the potential of further reducing the lead time for producing a casting product. Some important issues, such as the lead time of producing a sand mould, its accuracy, and surface finish, etc., are discussed.