The growth and expression of virulence factors at refrigeration temperature by Aeromonas strains isolated from foods

Kirov, SM; Ardestani, Emad K.; Hayward, Laura J.

doi:10.1016/0168-1605(93)90108-s

Cited by 46 publications

(23 citation statements)

References 25 publications

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“…Disease-associated strains possess a number of significant virulence determinants, including the ability to produce type IV pilus adhesins (14-16, 20, 30, 31) and the pore-forming toxin "aerolysin" (18,50). Many Aeromonas strains grow at refrigeration temperatures, increasing concern about food-borne transmission (25,26). Yet relatively little is known of the pathogenic mechanisms of Aeromonas species, and it is not possible to identify virulent strains definitively.…”

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Investigation of the Role of Type IV Aeromonas Pilus (Tap) in the Pathogenesis of Aeromonas Gastrointestinal Infection

et al. 2000

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Although there is substantial evidence that type IV pili purified from diarrhea-associated Aeromonas species (designated Bfp for bundle-forming pilus) are intestinal colonization factors (S. M. Kirov, L. A. O'Donovan, and K. Sanderson, Infect. Immun. 67:5447-5454, 1999), nothing is known regarding the function of a second family of Aeromonas type IV pili (designated Tap for type IV Aeromonas pilus), identified following the cloning of a pilus biogenesis gene cluster tapABCD. Related pilus gene clusters are widely conserved among gramnegative bacteria, but their significance for virulence has been controversial. To investigate the role of Tap pili in Aeromonas pathogenesis, mutants of Aeromonas strains (a fish isolate of A. hydrophila and a human dysenteric isolate of A. veronii bv. sobria) were prepared by insertional inactivation of the tapA gene which encodes the type IV pilus subunit protein, TapA. Exotoxic activities were unaffected by the mutation in tapA. Inactivation of tapA had no effect on the bacterial adherence of these two isolates to HEp-2 cells. For the A. veronii bv. sobria isolate, adhesion to Henle 407 intestinal cells and to human intestinal tissue was also unaffected. There was no significant effect on the duration of colonization or incidence of diarrhea when the A. veronii bv. sobria strain was tested in the removable intestinal tie adult rabbit diarrhea model or on its ability to colonize infant mice. Evidence was obtained that demonstrated that TapA was expressed by both Aeromonas species and was present on the cell surface, although if assembled into pili this pilus type appears to be an uncommon one under standard bacterial growth conditions. Further studies into factors which may influence Tap expression are required, but the present study suggests that Tap pili may not be as significant as Bfp pili for Aeromonas intestinal colonization.

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Investigation of the Role of Type IV Aeromonas Pilus (Tap) in the Pathogenesis of Aeromonas Gastrointestinal Infection

et al. 2000

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“…Isolation of A. hydrophila from water and food sources, as well as the increasing resistance of this organism to antibiotics and chlorination in water, presents a significant threat to public health (2,4,10,11,16,26,27,30,34,48). Although Aeromonas-induced gastroenteritis is most common in young children, the organism is being isolated lately with high frequency from patients with traveler's diarrhea (14,48).…”

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“…After initial colonization of the epithelial cells through type IV pili (8,30,31,32), A. hydrophila may cause diarrhea by producing enterotoxins (14,33). Asao et al (6) first purified a 49-to 52-kDa ␤-hemolysin to homogeneity from a species of Aeromonas that induced fluid secretion in an animal model.…”

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Role of Various Enterotoxins in Aeromonas hydrophila- Induced Gastroenteritis: Generation of Enterotoxin Gene-Deficient Mutants and Evaluation of Their Enterotoxic Activity

2002

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Three enterotoxins from the Aeromonas hydrophila diarrheal isolate SSU have been molecularly characterized in our laboratory. One of these enterotoxins is cytotoxic in nature, whereas the other two are cytotonic enterotoxins, one of them heat labile and the other heat stable. Earlier, by developing an isogenic mutant, we demonstrated the role of a cytotoxic enterotoxin in causing systemic infection in mice. In the present study, we evaluated the role of these three enterotoxins in evoking diarrhea in a murine model by developing various combinations of enterotoxin gene-deficient mutants by marker-exchange mutagenesis. A total of six isogenic mutants were prepared in a cytotoxic enterotoxin gene (act)-positive or -negative background strain of A. hydrophila. We developed two single knockouts with truncation in either the heat-labile (alt) or the heat-stable (ast) cytotonic enterotoxin gene; three double knockouts with truncations of genes encoding (i) alt and ast, (ii) act and alt, and (iii) act and ast genes; and a triple-knockout mutant with truncation in all three genes, act, alt, and ast. The identity of these isogenic mutants developed by double-crossover homologous recombination was confirmed by Southern blot analysis. Northern and Western blot analyses revealed that the expression of different enterotoxin genes in the mutants was correspondingly abrogated. We tested the biological activity of these mutants in a diet-restricted and antibiotic-treated mouse model with a ligated ileal loop assay. Our data indicated that all of these mutants had significantly reduced capacity to evoke fluid secretion compared to that of wild-type A. hydrophila; the triple-knockout mutant failed to induce any detectable level of fluid secretion. The biological activity of selected A. hydrophila mutants was restored after complementation. Taken together, we have established a role for three enterotoxins in A. hydrophila-induced gastroenteritis in a mouse model with the greatest contribution from the cytotoxic enterotoxin Act, followed by the Alt and Ast cytotonic enterotoxins.

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“…have been cultured from both freshwater and salt water and from many foods. These bacteria have emerged as important human pathogens and are being isolated in an increased incidence from patients with traveler's diarrhea (3,11,28,29,41,44,70). Aeromonas spp.…”

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The Cytotoxic Enterotoxin ofAeromonas hydrophilaInduces Proinflammatory Cytokine Production and Activates Arachidonic Acid Metabolism in Macrophages

et al. 2000

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An aerolysin-related cytotoxic enterotoxin (Act) of Aeromonas hydrophila possesses multiple biological activities, which include its ability to lyse red blood cells, destroy tissue culture cell lines, evoke a fluid secretory response in ligated intestinal loop models, and induce lethality in mice. The role of Act in the virulence of the organism has been demonstrated. In this study, we evaluated the potential of Act to induce production of proinflammatory cytokines associated with Act-induced tissue injury and Act's capacity to activate in macrophages arachidonic acid (AA) metabolism that leads to production of eicosanoids (e.g., prostaglandin E 2 [PGE 2 ]). Our data indicated that Act stimulated the production of tumor necrosis factor alpha and upregulated the expression of genes encoding interleukin-1␤ (IL-1␤) and IL-6 in the murine macrophage cell line RAW264.7. Act also activated transcription of the gene encoding inducible nitric oxide synthase. Act evoked the production of PGE 2 coupled to the cyclooxygenase-2 (COX-2) pathway. AA is a substrate for PGE 2 , and Act produced AA from phospholipids by inducing group V secretory phospholipase A 2 . We also demonstrated that Act increased cyclic AMP (cAMP) production in macrophages. cAMP, along with PGE 2 , could potentiate fluid secretion in animal models because of infiltration and activation of macrophages resulting from Act-induced tissue injury. After Act treatment of RAW cells, we detected an increased translocation of NF-B and cAMP-responsive element binding protein (CREB) to the nucleus using gel shift assays. Act also upregulated production of antiapoptotic protein Bcl-2 in macrophages, suggesting a protective role for Bcl-2 against cell death induced by proinflammatory cytokines. The increased expression of genes encoding the proinflammatory cytokines, COX-2, and Bcl-2 appeared correlated with the activation of NF-B and CREB. This is the first report of the detailed mechanisms of action of Act from A. hydrophila.Aeromonas spp. recently have been placed in the family Aeromonadaceae. They cause both intestinal and nonintestinal infections in humans (12), and, unlike gastroenteritis, which generally occurs in young children, these nonintestinal infections are often fatal and involve adults (36). Aeromonas spp. have been cultured from both freshwater and salt water and from many foods. These bacteria have emerged as important human pathogens and are being isolated in an increased incidence from patients with traveler's diarrhea (3,11,28,29,41,44,70). Aeromonas spp. produce an array of virulence factors, and the pathogenesis of Aeromonas infections is therefore complex and multifactorial (2). These virulence factors include hemolysins, cytotoxins, enterotoxins, proteases, lipases/phospholipases, leucocidin, endotoxin, fimbriae or adhesins, and the capacity to form an S-layer (17,45,47). Aeromonas hydrophila has been shown to be invasive for HEp-2 cell monolayers, and the bacterial cells adhere to human erythrocytes (6, 26). Two distinct families of type IV ...

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The growth and expression of virulence factors at refrigeration temperature by Aeromonas strains isolated from foods

Cited by 46 publications

References 25 publications

Investigation of the Role of Type IV Aeromonas Pilus (Tap) in the Pathogenesis of Aeromonas Gastrointestinal Infection

Investigation of the Role of Type IV Aeromonas Pilus (Tap) in the Pathogenesis of Aeromonas Gastrointestinal Infection

Role of Various Enterotoxins in Aeromonas hydrophila- Induced Gastroenteritis: Generation of Enterotoxin Gene-Deficient Mutants and Evaluation of Their Enterotoxic Activity

The Cytotoxic Enterotoxin ofAeromonas hydrophilaInduces Proinflammatory Cytokine Production and Activates Arachidonic Acid Metabolism in Macrophages

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