Particle agglutination assays to identify fibronectin and collagen cell surface receptors and lectins in Aeromonas and Vibrio species

Cytotoxic effects of Aeromonas hydrophila culture supernatant on peripheral blood leukocytes of Nile tilapia (Oreochromis niloticus): Possible presence of a secreted cytotoxic lectin

Number of exotoxins like haemolysin, leukocidin, aerolysin etc. were reported from Aeromonas hydrophila. In this study, we report the haemolytic and cytotoxic effect of A. hydrophila culture supernatant (CS) that is specifically inhibited by lactose and also by serum and mucus of Nile tilapia (Oreochromis niloticus). Hence, we assume the presence of a secreted lectin in the CS. CS is toxic to peripheral blood leukocytes (PBL) of O. niloticus as revealed by MTT assay and by flow cytometry. DNA laddering assay indicates that CS causes necrosis to PBL. As a result of necrosis, CS treated PBL showed increased production of reactive oxygen species as indicated by nitroblue tetrazolium and 2',7' -dichlorofluorescin diacetate assays. CS treated PBL showed reduced mRNA expression of TNF-α and IFN-γ genes. When CS was subjected to polyacrylamide gel electrophoresis, it showed a single band corresponding to the molecular weight of 45 kDa. However, upon concentrating the CS by ultrafiltration, many bands were visualized. Further studies at molecular level are required to unravel this macromolecular-leukocyte interaction which would ultimately benefit the aquaculture industry.

Adhesive properties of a LamB-like outer-membrane protein and its contribution to Aeromonas veronii adhesion

AIMS

To identify and characterize nonfimbrial proteins from Aeromonas veronii involved in the attachment to epithelial cells in vitro.

METHODS AND RESULTS

Two Aer. veronii mucin- and lactoferrin-binding proteins with molecular masses of 37 and 48 kDa were identified by Western blot analysis. According to its N-terminal amino acid sequence, the 48-kDa protein was identified as Omp48, an outer-membrane protein similar to LamB of Escherichia coli. LamB is a well-known porin involved in maltose transport across the outer membrane in E. coli. In a microtitre plate assay, Omp48 bound to the immobilized extracellular matrix proteins collagen and fibronectin, and the mucin- and lactoferrin-binding activity was confirmed. Adhesion of Omp48 to mucin, lactoferrin and collagen was diminished by preincubation with homologous glycoproteins or other carbohydrates, suggesting a putative Omp48 lectin-like binding domain. Anti-Omp48 antiserum significantly inhibited the Aer. veronii adhesion to confluent HeLa cell monolayers and pretreatment of cells with purified Omp48 elicited competitive inhibition of adhesion. Similarly, cross-inhibition of Aer. hydrophila and Aer. caviae adhesion was achieved with the same treatments, indicating the existence of a conserved surface protein among these species.

CONCLUSIONS

Taken together, these data indicate that Omp48 is involved in Aer. veronii adhesion to epithelial cells and might be an alternative adhesion factor of this micro-organism.

SIGNIFICANCE AND IMPACT OF THE STUDY

The adhesive potential of Aeromonas spp. is correlated with pathogenicity; however, the adhesion mechanism is complex and not well understood. This study provides evidence of a putative adhesion factor that might be contributing to pathogenicity of Aer. veronii and could be used for vaccine development.

Molecular cloning, sequencing and characterization of omp48, the gene encoding for an antigenic outer membrane protein from Aeromonas veronii

AIMS

To clone, sequence and characterize the gene encoding the Omp48, a major outer membrane protein from Aeromonas veronii.

METHODS AND RESULTS

A genomic library of Aer. veronii was constructed and screened to detect omp48 gene sequences, but no positive clones were identified, even under low stringency conditions. The cloned gene probably was toxic to the host Escherichia coli strain, so the cloning of omp48 was achieved by inverse PCR. The nucleotide sequence of omp48 consisted of an open reading frame of 1278 base pairs. The predicted primary protein is composed of 426 amino acids, with a 25-amino-acid signal peptide and common Ala-X-Ala cleavage site. The mature protein is composed of 401 amino acids with a molecular mass of 44,256 Da.

CONCLUSIONS

The omp48 gene from Aer. veronii was cloned, sequenced and characterized in detail. BLAST analysis of Omp48 protein showed sequence similarity (over 50%) to the LamB porin family from other pathogenic Gram-negative bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacterial diseases are a major economic problem for the fish farming industry. Outer membrane proteins are potentially important vaccine components. The characterization of omp48 gene will allow further investigation of the potential of Omp48 as recombinant or DNA vaccine component to prevent Aer. veronii and related species infections in reared fish.

Mucosal immune response of spotted sand bass Paralabrax maculatofasciatus (Steindachner, 1868) orally immunised with an extracellular lectin of Aeromonas veronii

To assess the immunogenic and immunoprotective role of the extracellular lectin from Aeromonas veronii (MCBP), which has affinity for mucosal constituents such as mucin, lactoferrin, immunoglobulins and collagen, spotted sand bass (Paralabrax maculatofasciatus) were orally immunised either with soluble MCBP, adjuvant-conjugated MCBP or immobilised MCBP on latex microspheres. The results suggest that the MCBP is capable of eliciting protective immunity against A. veronii infections when administered orally. The highest mucosal immune response was elicited in fish immunised with MCBP covalently linked to cholera toxin B subunit (CTB) or to Escherichia coli heat-labile toxin (hLT). MCBP-CTB was found to elicit immunoprotection against a challenge with live Aeromonas cells with a relative percent survival of almost 70% and without the expression of the severe histopathological alterations induced by A. veronii.

Biochemical characterization of different types of adherence of Vibrio species to fish epithelial cells

Vibrio species are Gram-negative bacteria that cause a systemic infection in fish called vibriosis. The authors previously demonstrated that internalization and cytotoxicity are important virulence mechanisms in vibrio-fish epithelial cell interactions. Adherence is a prerequisite for successful internalization. In this study, the adherence capability of two invasive strains [V. anguillarum 811218-5W and G/Virus/5(3)] was compared with that of two non-invasive strains [V. damselae ATCC 33539 and V. anguillarum S2/5/93(2)] using adherence assays in three different types of fish cells (epithelial papillosum of carp, EPC; grunt-fin tissue, GF; and fat-head minnow epithelial cells, FHM). For all four strains there was no significant difference (P>0.05) in the adherence to the different cell lines. V. anguillarum 811218-5W exhibited the highest adherence, followed by G/Virus/5(3) and S2/5/93(2); V. damselae ATCC 33539 showed the lowest adherence. The super-adherence characteristic of V. anguillarum 811218-5W on EPC cells was not affected by inhibitors, sugars, low temperature (4 degrees C) incubation, or non-biological surfaces such as glass coverslips. The galactose-linked adherence characteristic of V. anguillarum G/Virus/5(3) to the EPC cells was partially inhibited by peptidase treatment of the fish cells, low-temperature incubation, and addition of sugars that contained galactose (such as lactose and N-acetyl-D-galactosamine). De novo synthesis of bacterial protein, viable bacteria and intact carbohydrate structure of vibrios were required for both super-adherence and galactose-linked adherence. These adherence characteristics were also found in ten other invasive vibrios, and galactose-linked adherence was found in nine invasive vibrios.

Fibronectin and laminin binding of urogenital and oral prevotella species

88 strains of five Prevotella species--P. bivia, P. buccae, P. disiens, P. oralis, and P. oris--were examined for their fibronectin and laminin binding properties with the aid of latex particle agglutination assays. Beside single protein binding activities, all species showed strains that adhered to both fibronectin and laminin. The oral species, P. buccae, P. oralis, and P. oris were found to interact with laminin to a pronouncedly higher extent than with fibronectin. The urogenital species, P. bivia and P. disiens showed comparable activities of binding to fibronectin and laminin, with P. bivia exhibiting higher matrix protein binding rates than P. disiens. Within the oral species group, P. oralis showed a higher percentage of fibronectin and laminin reactive strains than did P. buccae and P. oris. The finding of species-related different binding properties may throw some light on the known differences in clinical relevance and pathogenicity of the urogenital species, P. bivia and P. disiens, but does so only in part concerning the oral species, P. buccae, P. oralis, and P. oris. Moreover, the observed differences in matrix protein binding of Prevotella species may have implications in chemotaxis and opsonization on the one hand and maintenance of colonization activities under antibiotic therapy on the other.

Fibronectin and laminin binding of eighteen Clostridium species

The ability of Clostridium difficile, Clostridium perfringens, Clostridium sporogenes and fifteen other Clostridium species to bind to human serum fibronectin or laminin was tested by using protein-coated latex particles. Three groups of Clostridium species were formed, namely the pseudomembranous colitis-causing species Clostridium difficile, the gas gangrene-causing Clostridium species and other Clostridium species, which are infrequently found in human infections. Significantly more strains of gas gangrene-causing Clostridium species, and strains of Clostridium species other than Clostridium difficile recognized fibronectin or laminin than did Clostridium difficile. Experiments with monoclonal antibodies revealed the specificity of the bacterial binding to fibronectin or laminin.

Cell-surface charge and cell-surface hydrophobicity of collagen-binding Aeromonas and Vibrio strains

Partitioning in aqueous polymer two-phase systems of polyethylene glycol and dextran was used to detect and compare cell-surface charge and cell-surface hydrophobicity of Aeromonas hydrophila, A. caviae, A. sobria, Vibrio cholerae, and V. anguillarum strains. These strains have cell-surface components that bound either native or thermally denatured type I collagen (i.e., a mixture of the alpha1+alpha2 chains) and gelatin immobilized on latex beads. Our goals were: (1) to compare the possible relationship between the cell-surface charge/hydrophobicity and binding to collagen and (2) to evaluate the influence of the culture media on the expression of surface properties. There was no apparent relationship between cell-surface charge, cell-surface hydrophobicity, and binding to collagen. The expression of surface properties was dependent on the culture media. There was no relationship between binding to immobilized collagen and binding to soluble 125I-labeled collagen. Particle-agglutination reactivity differed when using various collagen-coated microbead preparations. There were general differences in the particle-agglutination reactivity when collagen-coated latex beads were prepared using different coating procedures. The negative charge and hydrophobicity of the various collagen-coated microbead preparations were also studied by partitioning in the two-phase system of polyethylene glycol and dextran. Under these conditions, the alpha1+alpha2 collagen-chain mixture covalently immobilized on carboxy-modified latex beads was less hydrophobic and negatively charged than gelatin and native collagen immobilized on the same kind of latex beads. For latex beads passively coated with collagen preparations, the alpha1+alpha2 collagen-chain mixture was more hydrophobic than gelatin and native collagen. We suggest that for screening collagen-binding among Vibrio and Aeromonas strains, a reliable and sensitive particle-agglutination assay should consider the collagen preparation and the coating procedure for the immobilization of collagen onto the latex beads. In this regard, carboxy-modified latex beads coated with an alpha1+alpha2 collagen-chain mixture gave the best results.

Cell-surface properties of the food- and water-borne pathogen Aeromonas hydrophila when stored in buffered saline solutions

Aeromonas hydrophila, a ubiquitous inhabitant of aquatic environments, commonly expresses several cell-surface properties that may contribute to virulence. Since many aquatic microorganisms in hostile environments can withstand starvation conditions for long periods, we examined the effect of storage under nutrient-poor conditions on the expression of cell-surface properties of this pathogen. Phenotypes studied were: (1) cell-surface hydrophobicity and charge, and (2) the ability to bind connective-tissue proteins and lactoferrin. Our results suggest that the response of A. hydrophila to nutrient-poor conditions is regimen specific. Generally, A. hydrophila cells became more hydrophobic and significantly increased their ability to bind the iron-binding glycoprotein lactoferrin when the bacterium was stored under nutrient-poor conditions; however, under these conditions, the cells seemed to lose their ability to bind connective-tissue proteins.

Bacteroides fragilis adheres to laminin significantly stronger than Bacteroides thetaiotaomicron and other species of the genus

The laminin binding properties of eight species of the genus Bacteroides were examined using latex particle agglutination assay. B. fragilis was found to bind strongly to laminin, whereas all other species tested showed no or only weak laminin adherence. The pronounced differences in laminin binding activity between B. fragilis on the one side and B. thetaiotaomicron and B. ovatus on the other were determined to be statistically significant (p < 0.001 and p < 0.01, respectively). With regard to the relevance of laminin adherence for bacterial pathogenicity and invasiveness, our results give a possible explanation for the well-known finding that B. fragilis is the most frequently isolated pathogen in anaerobic bacteremia.

Effects of a water-soluble ethylhydroxyethyl cellulose on gut physiology, bacteriology, and bacterial translocation in acute liver failure

Bacterial infection and bacteremia are common complications in patients with acute liver failure. Bacterial translocation from the gut has been suggested to be a major cause of bacterial infections in experimental acute liver failure. In the present study, a water-soluble ethylhydroxyethyl cellulose (EHEC) was administered orally 1 and 24 hours prior to 90% hepatectomy in the rat in order to prevent bacterial translocation in experimental acute liver failure induced by subtotal liver resection in the rat. Ninety percent hepatectomy alone resulted in 80 to 100% translocation to mesenteric lymph nodes or blood 2 and 4 hours after operation. There was no translocation in rats undergoing sham operation or 90% hepatectomy with EHEC administration prior to operation (p < .01). Bacterial overgrowth, increased bacterial adherence onto the intestinal surface, and diminished intestinal and mucosal mass were also observed in animals with subtotal liver resection, but not in those administered EHEC. A delayed 2-hour intestinal transit time occurred in both groups receiving subtotal liver resection, with or without oral EHEC. EHEC inhibited bacterial growth and DNA synthesis and altered bacterial surface properties after 1-hour incubation with bacteria in vitro, an interaction that was not further influenced by time. These results imply that EHEC may alter enterobacterial capacities of metabolism, proliferation, and invasion by effects on the bacterial surface. Furthermore, EHEC seems to possess a trophic action on the intestine, though without enhancing the intestinal motility.

Rapid detection and characterization of sialic acid-specific lectins of Helicobacter pylori

A particle agglutination assay (PAA) using fetuin (Ft) covalently coupled to carboxylate-modified latex (CML) particles was evaluated for rapid detection of sialic acid-specific haemagglutinins/lectins (SALs) of Helicobacter pylori isolates which bind sialoglycoconjugates. Sixty-three percent (20/32) of the isolates examined gave a positive PAA test. Cell-bound SALs were extracted by washing the bacteria with deionized water or isotonic saline, and their expression was influenced by pH and culture conditions. The Ft-CML reactivity of the PAA-positive isolates was inhibited by bovine submaxillary mucin, transferrin, fetuin, orosomucoid, vitronectin and lactoferrin in a manner which suggested that the isolates contain a lectin recognizing the alpha(2-6) linkage of terminal sialic acid. Western blots of strain NCTC 11637 SALs probed with horseradish peroxidase (HRP)-labelled Ft identified three bands (MW 64 kD, 62 kD, 56 kD) which also reacted with HRP-labelled mucin, transferrin, lactoferrin, orosomucoid, vitronectin and laminin. Sera from patients with a H. pylori infection and one polyclonal rabbit antiserum (strain NCTC 11637) also reacted with the SALs. Immunogold labelling of a polyclonal rabbit antiserum raised against the 64 kD protein of strain NCTC 11637 that reacted strongly with Ft-CML showed that abundant SALs were loosely cell-associated with the cell surface of both spiral and coccoidal forms of H. pylori. SALs were also present in low amounts on the surface of strain NCTC 11638 and 66, a clinical isolate that did not react with Ft-CML.

Binding of collagen, fibronectin, lactoferrin, laminin, vitronectin and heparan sulphate to Staphylococcus aureus strain V8 at various growth phases and under nutrient stress conditions

We have examined how Staphylococcus aureus strain V8 cells interact with 125I-labelled extracellular matrix (ECM) and serum proteins (collagen type I and IV), fibronectin, lactoferrin, laminin, vitronectin, and heparan sulphate at various phases of the growth cycle. Maximal binding of these glycoproteins and heparan sulphate to the bacteria occurred after 17 to 20 h in the late stationary phase except for fibronectin-binding, which was maximal after 12 to 14 h. Binding of the glycoproteins and heparan sulphate to S. aureus V8 under nutrient stress conditions exhibited complex patterns based on different starving conditions and various binding ligands. In general, bacteria starved in distilled water and 0.02 M potassium phosphate buffer (pH 7.2) at room temperature showed high susceptibility to all binding ligands within the first 18 h, followed by entering a lower binding period (except for collagen-binding which still remained high). The binding was not correlated to cell surface charge or hydrophobicity of the bacteria. Furthermore, extracellular and cell-associated proteolytic activity of starved cells against ECM and serum proteins was found to be greater than for non-starved cells. Thus, S. aureus could sustain its ability to bind various connective tissue and cell surface components during a long period of time even in the absence of energy-yielding substrates.

Purification and characterization of Aeromonas sobria Ae24 pili: a possible new colonization factor

Pili of Aeromonas sobria Ae24 were purified and characterized. The molecular mass of the pilin was estimated to be about 19 kDa by SDS-PAGE. The Ae24 pili were electrophoretically distinguishable from previously reported Aeromonas hydrophila Ae6 W pili and A. sobria Ae1 pili, although all three had indistinguishable morphology and shared a high degree of homology in the N-terminal amino acid sequences. Strain Ae24 and its purified pili adhered to rabbit intestine and agglutinated human and rabbit erythrocytes. Hemagglutination was inhibited by D-galactose and D-mannose, but not by L-fucose. Organisms pretreated with Fab fraction of the antipilus antibody failed to adhere to the intestine. Organisms did not adhere to intestine pretreated with the purified pili. These findings suggest that the pili are a colonization factor of A. sobria Ae24 for the rabbit intestine, and that the receptor is galactose- and mannose-containing structure.

Water-soluble ethylhydroxyethyl cellulose prevents bacterial translocation induced by major liver resection in the rat

Enteric bacteria might act as pathogens, translocating across the intestinal barrier to extraintestinal sites after major liver resection. In the current study, water-soluble ethylhydroxyethyl cellulose (EHEC) was administered before hepatectomy to evaluate the influence on bacterial translocation induced by major liver resection, phagocytic capacity by visceral and circulating macrophages, enteric bacterial population, and bacterial adherence on the intestinal surface in rats subjected to sham operation or to 70% or 90% hepatectomy. Oral or intravenous (IV) administration of EHEC reduced the incidence of bacterial translocation to mesenteric lymph nodes (MLN) and blood after major liver resection. Oral EHEC appeared more effective than IV administration in protecting against bacterial translocation to MLN in animals with 90% hepatectomy. Ethylhydroxyethyl cellulose (oral and IV) significantly diminished intestinal macrophage uptake capacity of 125I-labeled, heat-killed Escherichia coli as compared with animals without EHEC administration. Overgrowth or colonization of enteric bacteria after major liver resection could be prevented by oral or IV EHEC. Adherence of 14C-labeled, alive E. coli on the intestinal mucosa decreased after EHEC treatment in animals subjected to major liver resection. Systemic arterial pressure and intestinal blood flow markedly decreased from 1 hour and on after 90% hepatectomy. Intravenous administration of EHEC did not improve these alterations. Bacterial hydrophobicity and surface negative charge were significantly reduced 1 hour after bacterial culture with EHEC. Thus, EHEC appears to be a potent agent preventing translocation of enteric bacteria from the gut after major liver resection, by altering the surface characters of enteric bacteria, balancing the enteric microflora, inhibiting bacterial attachment onto the intestinal surface, and blocking phagocytosis by intestinal macrophages.

Binding of Escherichia coli to Penrose rubber drains--an in vitro study

Ten different isolates of Escherichia coli were used to compare bacterial attachment to Penrose rubber drains at different temperatures and to investigate a possible relation with cell surface hydrophobicity and charges, as well as the capacity of autoaggregation. Penrose rubber drain pieces of 1 cm2 were incubated with 4.8 x 10(6) E. coli cells for 1 h at 22, 37 and 42 degrees C, respectively. After rinsing with phosphate buffered saline (PBS), the number of adhering bacteria on the drain pieces was calculated by measuring cellular ATP (adenosine triphosphate) bioluminescence. Bacterial cell surface properties at different temperatures were determined by two-phase partitioning and autoaggregation was determined by arbitrary scoring under the dissecting microscope. For most strains of E. coli, the number of adherence to Penrose rubber drain was higher at 22 degrees C than at 37 degrees C and 42 degrees C. Bacterial cell-surface properties and autoaggregation capacity were influenced by the growth temperature, but without correlation to bacterial ability to attach to rubber drains. Thus, the present study demonstrates that attachment of E. coli to Penrose rubber drains was significantly influenced by temperature, but bacterial cell-surface hydrophobicity and charge as well as autoaggregation capacity had no influence on bacterial attachment ability.

Toxoplasma gondii: uptake of fetuin and identification of a 15-kDa fetuin-binding protein

Lectin-binding studies demonstrated the presence of a 68-kDa glycoprotein in tachyzoites of Toxoplasma gondii harvested from P388D1 macrophage cell cultures but not in tachyzoites maintained in peritoneal cavities of NMRI mice. This protein was identified as the embryonic protein fetuin that regularly is contained in fetal calf serum, a component of cell-culture media. Uptake of fetuin by T. gondii was demonstrated by intracellular localization of this protein. As shown by latex agglutination and immunofluorescence, no specific binding of fetuin to the parasite's surface was detected. Using affinity chromatography on fetuin-agarose, it was demonstrated that fetuin bound specifically to a 15-kDa antigen of tachyzoites. As revealed by inhibition studies with sialic acid and the lectin Sambucus nigra agglutinin, the 15-kDa protein probably recognized glycan structures of fetuin.

Rapid identification of fibronectin, vitronectin, laminin, and collagen cell surface binding proteins on coagulase-negative staphylococci by particle agglutination assays

Seventeen strains of ten different species of coagulase-negative staphylococci were shown to interact with collagen, laminin, fibronectin, and vitronectin immobilized on latex beads. Different species of coagulase-negative staphylococci have different capacities to agglutinate proteins. Cells of 18 strains of Staphylococcus haemolyticus reacted more strongly than did cells of 18 Staphylococcus epidermidis strains with proteincoated latex beads, although no significant difference in cell surface hydrophobicity or charge could be shown. The cell surface receptors of S. haemolyticus were more heat and protease resistant than were Staphylococcus aureus receptors. Strains of Staphylococcus saprophyticus isolated from urinary tract infections showed a high capacity to adhere to laminin. The ability to agglutinate fibronectin and collagen was common among coagulase-negative staphylococci isolated from other infections; 55% (31 of 56) and 63% (35 of 56) agglutinated fibronectin and/or collagen. S. haemolyticus and S. epidermidis bound to both N-terminal (29-kDa) and C-terminal (120-kDa) fragments of fibronectin.

Binding of Haemophilus ducreyi to extracellular matrix proteins

A collection of Haemophilus ducreyi isolates were screened for the ability to bind to fibrinogen, fibronectin, collagen, gelatin and laminin by a particle agglutination test using latex beads coated with the individual proteins. Thirteen of 21 isolates reacted with all five extracellular matrix proteins. Binding of organisms to protein-coated latex beads was inhibited by pretreatment of the bacteria with detergent, trypsin or boiling. Two isolates did not bind to collagen and gelatin with one of these not reacting with laminin either. Seven strains which failed to react with laminin did not express pili when examined by electron microscopy. This observation suggests a specific interaction with the pili of H. ducreyi.

Characterization of lactoferrin binding by Aeromonas hydrophila

Various lactoferrin preparations (iron-saturated and iron-depleted human milk lactoferrins and bovine milk and colostrum lactoferrins) were bound by Aeromonas hydrophila. Binding was (i) reversible (65% of bound lactoferrin was displaced by unlabeled lactoferrin), (ii) specific (lactoferrin but not other iron-containing glycoproteins such as ferritin, transferrin, hemoglobin, and myoglobin inhibited binding), and (iii) significantly reduced by pepsin and neuraminidase treatment of the bacteria. The glycosidic domains of the lactoferrin molecule seem to be involved in binding since precursor monosaccharides of the lactoferrin oligosaccharides (mannose, fucose, and galactose) and glycoproteins which have homologous glycosidic moieties similar to those of the lactoferrin oligosaccharides (asialofetuin or fetuin) strongly inhibited lactoferrin binding. A. hydrophila also binds transferrin, ferritin, cytochrome c, hemin, and Congo red. However, binding of these iron-containing compounds seems to involve bacterial surface components different from those required for lactoferrin binding. Expression of lactoferrin binding by A. hydrophila was influenced by culture conditions. In addition, there was an inverse relationship between lactoferrin binding and siderophore production by the bacterium.

Surface properties, connective tissue protein binding and Shiga-like toxin production of Escherichia coli isolated from patients with ulcerative colitis

Escherichia coli strains isolated from intestinal biopsies of patients with ulcerative colitis (n 146), Crohn's disease and colonic polyposis (n 41) were analysed for binding of collagen I, collagen IV, fibronectin and laminin. Strains expressed varying degrees of binding of one or more of the four connective tissue proteins. Only 32 strains did not express binding of any of the proteins. The strains expressed low or moderate cell surface hydrophobicity. There was no correlation between protein binding and expression of cell surface hydrophobicity. E. coli isolated from inflamed rectal mucosa were slightly less negatively charged than strains isolated from healthy intestinal mucosa. Shiga-like toxins I and II were detected in 32 strains from 28 patients. Of these, 5 strains had been isolated from normal or healed tissue. In patients with inflammatory bowel disease, connective tissue proteins are exposed in intestinal ulcerations. Strains expressing binding of one or several of these proteins may have a selective advantage to colonize these lesions.

Fibronectin binding by Salmonella strains: evaluation of a particle agglutination assay

Thirty-five Salmonella strains isolated from human cases of salmonellosis were tested and compared for their fibronectin (fn) binding capacities by using two fn-particle agglutination assays (fn-PAAs) prepared by coating with human fn either (i) latex beads (Difco; 0.81-micron diameter) (L-fn-PAA) or (ii) heat-killed formalin-treated Staphylococcus aureus Cowan 1 cells (C-fn-PAA). Six S. aureus strains were also included in this study as controls. The strains were cultured on colonization factor antigen agar and blood agar and in tryptic soy broth and brain heart infusion broth. The Salmonella and S. aureus strains were cultured at 33 and 37 degrees C, respectively, for optimal expression of fn-binding proteins. Bacterial cells (approximately 10(10) cells per ml) harvested from growth in various culture media and suspended in 0.02 M potassium phosphate buffer (pH 6.8) agglutinated the fn-PAA reagents. These reactions were scored semiquantitatively from + to + depending on the speed or intensity of the reactions within 2 min. Maximum agglutination in fn-PAA systems was observed when the cells were grown in brain heart infusion broth, while tryptic soy broth proved to be least suitable media for culturing cells for fn-PAAS. Although a statistically highly significant correlation was obtained between results of assays of radiolabeled fn and 29-kDa fragment binding, no significant correlation was observed (i) between the results of strains cultured in different media or (ii) when semiquantitative score results of the two fn-PAA systems were compared with those of the conventional radiolabeled fn assay. To enhance the efficiency of the test system, the C-fn-PAA reagent was stained with methylene blue (2% in 0.17 M glycine-NaOH buffer [pH 6.8]). This facilitated easy interpretation of results, which could be performed on hydrophobic paper instead of glass slides. The results obtained with both unstained C-fn-PAA and stained C-fn-PAA were comparable to each other and reproducible. Although the fn-PAAs are simple and easy to perform, the results did not differentiate between negative, low, moderate, and high binding abilities when Salmonella strains were evaluated for fn binding, and the results were not comparable to those obtained by the conventional radiolabeling method.

Aeromonas and Plesiomonas as food- and waterborne pathogens

Aeromonas and Plesiomonas have become increasingly recognized as human enteropathogens. Plesiomonas shigelloides has mainly been recovered from various sea foods, whereas Aeromonas sp. have also been cultured from pigs, broilers, eggs, milk and vegetables. Aeromonas sp. also multiply rapidly at +4 degrees C which is a significant risk in food storage. Aeromonas sp. have furthermore been recovered from fresh water sources, and some isolates are resistant to chlorination which makes it a further risk factor. No large food- or waterborne outbreaks have been reported so far with Aeromonas sp. Various virulence factors involved in intestinal infections are described such as enterotoxins, cytotoxins, and adhesins.