Consequences of microbial attachment: directing host cell functions with adhesins

Evaluation of Selected Bacteria and Yeast for Probiotic Potential in Poultry Production

Performance and efficiency of feed utilization in poultry is highly influenced by gut health, which is dependent on intestinal microbial balance. Probiotics are live microbial feed supplements or viable microorganisms that beneficially affect the host animal by improving its gastrointestinal tract (GIT) microbial balance. However, their mode of action and suitable GIT environment favoring their colonization of the GIT is obscure. The probiotic properties of Lactobacillus plantarum, Bifidobacterium longum, and Saccharomyces boulardii were evaluated. These microbes were tested in vitro against gastrointestinal conditions for survivability and their ability to attach to the intestinal mucosa. The ability of the microbes to tolerate and survive varying pH levels and bile concentrations was assessed. The microbes were challenged with a pH of 2 to 7 for 5 h and bile concentrations of 1 to 3% for 6 hrs. The microbes were sampled hourly to evaluate growth or decline in colony-forming units (CFU). B. longum, L. Plantarum, and S. boulardii exhibited significantly higher CFU (p < 0.05) at a pH range of 5 to 7, 4 to 7, and 2 to 7, respectively, when compared with other pH levels. L. plantarum had much higher colony-forming units per mL within each pH level, except at pH 2 where S. boulardii was the only microbe to survive over time. While L. plantarum and S. boulardii were able to tolerate the various bile concentrations, B. longum and L. plantarum showed remarkable ability to attach to the intestinal mucosa and to inhibit pathogenic microbes.

Molecular insights into probiotic mechanisms of action employed against intestinal pathogenic bacteria

Gastrointestinal (GI) diseases, and in particular those caused by bacterial infections, are a major cause of morbidity and mortality worldwide. Treatment is becoming increasingly difficult due to the increase in number of species that have developed resistance to antibiotics. Probiotic lactic acid bacteria (LAB) have considerable potential as alternatives to antibiotics, both in prophylactic and therapeutic applications. Several studies have documented a reduction, or prevention, of GI diseases by probiotic bacteria. Since the activities of probiotic bacteria are closely linked with conditions in the host's GI-tract (GIT) and changes in the population of enteric microorganisms, a deeper understanding of gut-microbial interactions is required in the selection of the most suitable probiotic. This necessitates a deeper understanding of the molecular capabilities of probiotic bacteria. In this review, we explore how probiotic microorganisms interact with enteric pathogens in the GIT. The significance of probiotic colonization and persistence in the GIT is also addressed.

The Biology of the Mesothelium during Peritoneal Dialysis

Substantial derangements of mesothelial biology are observed during experimental simulations of dialysis conditions, inferred from the content of human dialysis effluent and visualized by microscopy of human mesothelial biopsies. Canosmotically active solutions be made biocompatible with the osmoregulatory system of the mesothelium? Can the contributions of the mesothelium to host defenses against inflammation and/or infection be supported during CAPD? Do underlying metabolic derangements present in various kidney diseases and end-stage renal disease, regardless of cause, require customized CAPD protocols and solutions? Use of dialysis solutions less directly toxic to the mesothelium is a necessary step toward some day manipulating peritoneal biology by pharmacological and therapeutic modalities.

Real-Time Imaging of Bacteria/Osteoblast Dynamic Coculture on Bone Implant Material in an in Vitro Postoperative Contamination Model

Biomedical implants are an important part of evolving modern medicine but have a potential drawback in the form of postoperative pathogenic infection. Accordingly, the "race for surface" combat between invasive bacteria and host cells determines the fate of implants. Hence, proper in vitro systems are required to assess effective strategies to avoid infection. In this study, we developed a real time observation model, mimicking postoperative contamination, designed to follow E. coli proliferation on a titanium surface occupied by human osteoblastic progenitor cells (STRO). This model allowed us to monitor E. coli invasion of human cells on titanium surfaces coated and uncoated with fibronectin. We showed that the surface colonization of bacteria is significantly enhanced on fibronectin coated surfaces irrespective of whether areas were uncovered or covered with human cells. We further revealed that bacterial colonization of the titanium surfaces is enhanced in coculture with STRO cells. Finally, this coculture system provides a comprehensive system to describe in vitro and in situ bacterial and human cells and their localization but also to target biological mechanisms involved in adhesion as well as in interactions with surfaces, thanks to fluorescent labeling. This system is thus an efficient method for studies related to the design and function of new biomaterials.

Evaluation of protective effect of Lactobacillus acidophilus La-5 on toxicity and colonization of Clostridium difficile in human epithelial cells in vitro

Clostridium difficile infection is a range of toxin - mediated intestinal diseases that is often acquired in hospitals and small communities in developed countries. The main virulence factors of C. difficile are two exotoxins, toxin A and toxin B, which damage epithelial cells and manifest as colonic inflammation and mild to severe diarrhea. Inhibiting C. difficile adherence, colonization, and reducing its toxin production could substantially minimize its pathogenicity and lead to faster recovery from the disease. This study investigated the efficacy of probiotic secreted bioactive molecules from Lactobacillus acidophilus La-5, in decreasing C. difficile attachment and cytotoxicity in human epithelial cells in vitro. L. acidophilus La-5 cell-free supernatant (La-5 CFS) was used to treat the hypervirulent C. difficile ribotype 027 culture with subsequent monitoring of cytotoxicity and adhesion. In addition, the effect of pretreating cell lines with La-5 CFS in protecting cells from the cytotoxicity of C. difficile culture filtrate or bacterial cell attachment was examined. La-5 CFS substantially reduced the cytotoxicity and cytopathic effect of C. difficile culture filtrate on HT-29 and Caco-2 cells. Furthermore, La-5 CFS significantly reduced attachment of the C. difficile bacterial cells on both cell lines. It was also found that pretreatment of cell lines with La-5 CFS effectively protected cell lines from cytotoxicity and adherence of C. difficile. Our study suggests that La-5 CFS could potentially be used to prevent and cure C. difficile infection and relapses.

Epigenetic Influence of Dam Methylation on Gene Expression and Attachment in Uropathogenic Escherichia coli

Urinary tract infections (UTI) are among the most frequently encountered infections in clinical practice globally. Predominantly a burden among female adults and infants, UTIs primarily caused by uropathogenic Escherichia coli (UPEC) results in high morbidity and fiscal health strains. During pathogenesis, colonization of the urinary tract via fimbrial adhesion to mucosal cells is the most critical point in infection and has been linked to DNA methylation. Furthermore, with continuous exposure to antibiotics as the standard therapeutic strategy, UPEC has evolved to become highly adaptable in circumventing the effect of antimicrobial agents and host defenses. Hence, the need for alternative treatment strategies arises. Since differential DNA methylation is observed as a critical precursor to virulence in various pathogenic bacteria, this body of work sought to assess the influence of the DNA adenine methylase (dam) gene on gene expression and cellular adhesion in UPEC and its potential as a therapeutic target. To monitor the influence of dam on attachment and FQ resistance, selected UPEC dam mutants created via one-step allelic exchange were transformed with cloned qnrA and dam complement plasmid for comparative analysis of growth rate, antimicrobial susceptibility, biofilm formation, gene expression, and mammalian cell attachment. The absence of DNA methylation among dam mutants was apparent. Varying deficiencies in cell growth, antimicrobial resistance and biofilm formation, alongside low-level increases in gene expression (recA and papI), and adherence to HEK-293 and HTB-9 mammalian cells were also detected as a factor of SOS induction to result in increased mutability. Phenotypic characteristics of parental strains were restored in dam complement strains. Dam's vital role in DNA methylation and gene expression in local UPEC isolates was confirmed. Similarly to dam-deficient Enterohemorrhagic E. coli (EHEC), these findings suggest unsuccessful therapeutic use of Dam inhibitors against UPEC or dam-deficient UPEC strains as attenuated live vaccines. However, further investigations are necessary to determine the post-transcriptional influence of dam on the regulatory network of virulence genes central to pathogenesis.

Tea and soybean extracts in combination with milk fermentation inhibit growth and enterocyte adherence of selected foodborne pathogens

This study examined the antibacterial and anti-adhesive properties of pure plant extracts (PPEs) of green tea (GT), black tea (BT) and soybean individually or in combination with milk. Fermented phenolic enriched-milk (fPEM) was prepared by combining PPEs with milk and fermented with lactic acid bacteria. Antimicrobial activity of extracts was evaluated by broth-dilution and agar diffusion assay. Anti-adhesive property of extracts was evaluated in Caco-2 cell model. Results from antibacterial tests showed that PPEs exhibited a dose-dependent growth inhibitory effect. Tea extracts were more effective in inhibiting Gram-positive bacteria while soybean extract exhibited similar effects against all pathogens tested. For fPEM, although total phenolic contents decreased compared with those in PPEs, growth inhibitory effect of fPEM containing tea extracts was greatly enhanced. All extracts showed significant inhibition against pathogen adhesion to Caco-2 cells. In particular, adhesion inhibition against Staphylococcus aureus and Listeria monocytogenes was >89% when fPEM extracts were applied.

Complement protective epitopes and CD55-microtubule complexes facilitate the invasion and intracellular persistence of uropathogenic Escherichia coli

BACKGROUND

 Escherichia coli-bearing Dr-adhesins (Dr+ E. coli) cause chronic pyelonephritis in pregnant women and animal models. This chronic renal infection correlates with the capacity of bacteria to invade epithelial cells expressing CD55. The mechanism of infection remains unknown.

METHODS

 CD55 amino acids in the vicinity of binding pocket-Ser155 for Dr-adhesin were mutated to alanine and subjected to temporal gentamicin-invasion/gentamicin-survival assay in Chinese hamster ovary cells. CD55/microtubule (MT) responses were studied using confocal/electron microscopy, and 3-dimensional structure analysis.

RESULTS

 Mutant analysis revealed that complement-protective CD55-Ser165 and CD55-Phe154 epitopes control E. coli invasion by coregulating CD55-MT complex expression. Single-point CD55 mutations changed E. coli to either a minimally invasive (Ser165Ala) or a hypervirulent pathogen (Phe154Ala). Thus, single amino acid modifications with no impact on CD55 structure and bacterial attachment can have a profound impact on E. coli virulence. While CD55-Ser165Ala decreased E. coli invasion and led to dormant intracellular persistence, intracellular E. coli in CD55-Phe154Ala developed elongated forms (multiplying within vacuoles), upregulated CD55-MT complexes, acquired CD55 coat, and escaped phagolysosomal fusion.

CONCLUSIONS

 E. coli target complement-protective CD55 epitopes for invasion and exploit CD55-MT complexes to escape phagolysosomal fusion, leading to a nondestructive parasitism that allows bacteria to persist intracellularly.

Normal to cancer microbiome transformation and its implication in cancer diagnosis

Microbial communities coexisting with humans are collectively known as microbiome. It influences almost every aspect of an individual's body function. Microbiome is idiosyncratic for body condition and its alteration is indicative for several abnormalities. This article discusses about recent ideas for developing microbiology based cancer indicators using alterations in microbiome. It is noteworthy that large exploratory studies are required to identify cancer indicator microorganisms from complex and diverse microbiome constituents. This complexity also warrants that these markers should be used in conjunction with other routine cancer indicators. The present article concludes that such studies can spur development of novel microbiome based cancer diagnostics.

Treponema denticola interactions with host proteins

Oral Treponema species, most notably T. denticola, are implicated in the destructive effects of human periodontal disease. Progress in the molecular analysis of interactions between T. denticola and host proteins is reviewed here, with particular emphasis on the characterization of surface-expressed and secreted proteins of T. denticola involved in interactions with host cells, extracellular matrix components, and components of the innate immune system.

Induction of Chitin-Binding Proteins during the Specific Attachment of the Marine Bacterium Vibrio harveyi to Chitin

Previous work has shown that attachment of Vibrio harveyi to chitin is specific and involves at least two chitin-binding peptides. However, the roles and regulation of these chitin-binding peptides in attachment are still unclear. Here we show that preincubation with the oligomeric sugars composing chitin stimulated chitinase activity, cellular attachment to chitin, and production of chitin-binding peptides. One of these peptides, a 53-kDa peptide, is produced constitutively and appears to mediate initial attachment to chitin. Synthesis of another peptide, a 150-kDa chitin-binding peptide, is induced by chitin and thus may be involved in time-dependent attachment. Coordinated regulation of attachment and degradation of chitin may give bacteria like V. harveyi a selective advantage over other bacteria in nutrient-poor aquatic environments.

Brucella melitensis VjbR and C12-HSL regulons: contributions of the N-dodecanoyl homoserine lactone signaling molecule and LuxR homologue VjbR to gene expression

Background

Quorum sensing is a communication system that regulates gene expression in response to population density and often regulates virulence determinants. Deletion of the luxR homologue vjbR highly attenuates intracellular survival of Brucella melitensis and has been interpreted to be an indication of a role for QS in Brucella infection. Confirmation for such a role was suggested, but not confirmed, by the demonstrated in vitro synthesis of an auto-inducer (AI) by Brucella cultures. In an effort to further delineate the role of VjbR to virulence and survival, gene expression under the control of VjbR and AI was characterized using microarray analysis.

Results

Analyses of wildtype B. melitensis and isogenic ΔvjbR transciptomes, grown in the presence and absence of exogenous N-dodecanoyl homoserine lactone (C₁₂-HSL), revealed a temporal pattern of gene regulation with variances detected at exponential and stationary growth phases. Comparison of VjbR and C₁₂-HSL transcriptomes indicated the shared regulation of 127 genes with all but 3 genes inversely regulated, suggesting that C₁₂-HSL functions via VjbR in this case to reverse gene expression at these loci. Additional analysis using a ΔvjbR mutant revealed that AHL also altered gene expression in the absence of VjbR, up-regulating expression of 48 genes and a luxR homologue blxR 93-fold at stationary growth phase. Gene expression alterations include previously un-described adhesins, proteases, antibiotic and toxin resistance genes, stress survival aids, transporters, membrane biogenesis genes, amino acid metabolism and transport, transcriptional regulators, energy production genes, and the previously reported fliF and virB operons.

Conclusions

VjbR and C₁₂-HSL regulate expression of a large and diverse number of genes. Many genes identified as virulence factors in other bacterial pathogens were found to be differently expressed, suggesting an important contribution to intracellular survival of Brucella. From these data, we conclude that VjbR and C₁₂-HSL contribute to virulence and survival by regulating expression of virulence mechanisms and thus controlling the ability of the bacteria to survive within the host cell. A likely scenario occurs via QS, however, operation of such a mechanism remains to be demonstrated.

Should yoghurt cultures be considered probiotic?

Probiotics are live micro-organisms that when administered in adequate amounts confer a health benefit on the host. Consumption of yoghurt has been shown to induce measurable health benefits linked to the presence of live bacteria. A number of human studies have clearly demonstrated that yoghurt containing viable bacteria (Streptococcus thermophilusandLactobacillus delbrueckiisp.bulgaricus) improves lactose digestion and eliminates symptoms of lactose intolerance. Thus, these cultures clearly fulfil the current concept of probiotics.

Variability of Clostridium difficile surface proteins and specific serum antibody response in patients with Clostridium difficile-associated disease

Pathogen attachment is a crucial early step in mucosal infections. This step is mediated by important virulence factors, such as surface proteins. Clostridium difficile surface proteins have been identified as (i) adhesins (the flagellar cap protein FliD; the flagellin FliC; and the cell wall protein Cwp 66 with a two domain-structure [Cw 66 N-terminal and Cwp 66 C-terminal domains]) and (ii) protease (the Cwp 84 protein). To address the roles of these proteins in the pathogenesis of Clostridium difficile and to identify vaccine antigen candidates, we analyzed the variability of the proteins and their immunogenicities in 17 patients with C. difficile-associated disease. PCR-restriction fragment length polymorphism analysis of amplified gene products revealed interstrain homogeneity with fliC and fliD, in contrast to cwp 66 genes. Immunoblot analysis showed that FliC and FliD were detected in the majority of isolates. The N-terminal domain of Cwp 66 and Cwp 84 were present in all strains tested, in contrast to the Cwp 66 C-terminal domain, the expression of which was heterogeneous. The 17 sera from the corresponding patients were analyzed by enzyme-linked immunosorbent assay to detect antibodies directed against these proteins. Many patients developed antibodies to FliC, FliD, Cwp 84, and the Cwp 66 C-terminal domain, but not to the Cwp 66 N-terminal domain. In conclusion, this study confirms the expression of these surface proteins of C. difficile during the course of the disease. In addition, the FliC, FliD, and Cwp 84 proteins appeared to be good potential vaccine candidates.

Dra/AfaE adhesin of uropathogenic Dr/Afa+ Escherichia coli mediates mortality in pregnant rats

Escherichia coli bearing adhesins of the Dr/Afa family frequently causes urogenital infections during pregnancy in humans and has been associated with mortality in pregnant rats. Two components of the adhesin, Dra/AfaE and Dra/AfaD, considered virulence factors, are responsible for bacterial binding and internalization. We hypothesize that gestational mortality caused by Dr/Afa+ E. coli is mediated by one of these two proteins, Dra/AfaE or Dra/AfaD. In this study, using afaE and/or afaD mutants, we investigated the role of the afaE and afaD genes in the mortality of pregnant rats from intrauterine infection. Sprague-Dawley rats, on the 17th day of pregnancy, were infected with the E. coli afaE+ afaD and afaE afaD+ mutants. The clinical E. coli strain (afaE+ afaD+) and the afaE afaD double mutant were used as positive and negative controls, respectively. The mortality rate was evaluated 24 h after infection. The highest maternal mortality was observed in the group infected with the afaE+ afaD+ strain, followed by the group infected with the afaE+ afaD strain. The mortality was dose dependent. The afaE afaD double mutant did not cause maternal mortality, even with the highest infection dose. The in vivo studies corresponded with the invasion assay, where the afaE+ strains were the most invasive (afaE+ afaD strain > afaE+ afaD+ strain), while the afaE mutant strains (afaE afaD+ and afaE afaD strains) seemed to be noninvasive. This study shows for the first time that the afaE gene coding for the AfaE subunit of Dr/Afa adhesin is involved in the lethal outcome of gestational infection in rats. This lethal effect associated with AfaE correlates with the invasiveness of afaE+ E. coli strains in vitro.

Surface morphology of pocket epithelium

The pocket epithelium in periodontitis differs from the clinically healthy epithelium in its increase in sulcular depth. However, closer surface morphological distinctions have not been described. To study the surface characteristics of pocket gingiva, the authors analyzed pocket and sulcular epithelium biopsies by scanning and transmission electron microscopy using cytochemical staining for visualization of bacterial adhesion. The clinically healthy and the marginal pocket epithelium were characterized by squamous epithelial cells joined by tight junctions and an inconspicuous surface lacking a distinctive papillary formation. The large quantity of bacteria that adhered to the clinically healthy and marginal pocket epithelium did not appear to elicit any significant defense response. The deeper part of the pocket epithelium revealed a wrinkled papillary relief, increased exfoliation of epithelial cells, leukocyte transmigration, and bacterial internalization, as well as internalization-induced epithelial apoptosis. The alteration of the deep pocket epithelium surface might be either genuine or due to environmental changes of the crevice, or both. Therefore, the periodontitis recovery after removing the deep pocket epithelium might now be related to the pathological alterations of the deep pocket epithelium.

Adherence of Actinobacillus pleuropneumoniae to primary cultures of porcine lung epithelial cells

To study adherence of Actinobacillus pleuropneumoniae to porcine lower respiratory epithelium, a cell culture model was developed using primary cultures of porcine lung epithelial cells (LEC). Adherence assays were performed and results were compared with data obtained with swine kidney cells (SK6). A. pleuropneumoniae efficiently adhered to LEC with up to 62 bacteria per cell after 2h of incubation. Reference strain of serotype 3 (R3) adhered better to LEC than reference strains of serotypes 1 (R1), 7 (R7) and 8 (R8). Overall the adherence to LEC was more rapid and up to 30-fold more efficient than adherence to SK6 cells. In search for the mechanism involved in the adherence event, we tested the effect of LPS which has previously been demonstrated to cause adherence of the pathogen to upper respiratory epithelium. Adherence assays with LPS transposon mutants demonstrated unaltered (mutant with modification in core/lipid A moiety) or even three-fold more adherence (mutants lacking O antigen) compared to the parent micro-organisms. Purified LPS of strains R1, R3, R7 and R8 did not inhibit adherence of R8 to LEC either, suggesting that LPS and particularly the O-antigen are not essential for adherence of A. pleuropneumoniae to LEC. The efficient, LPS-independent adherence of A. pleuropneumoniae to LEC cells indicates that A. pleuropneumoniae may carry different, cell type-specific adhesins and that primary cultures of lower respiratory epithelium are valuable infection models in studying A. pleuropneumoniae pathogenesis.

Role of adhesin release for mucosal colonization by a bacterial pathogen

Pathogen attachment is a crucial early step in mucosal infections. This step is mediated by important virulence factors called adhesins. To exert these functions, adhesins are typically surface-exposed, although, surprisingly, some are also released into the extracellular milieu, the relevance of which has previously not been studied. To address the role of adhesin release in pathogenesis, we used Bordetella pertussis as a model, since its major adhesin, filamentous hemagglutinin (FHA), partitions between the bacterial surface and the extracellular milieu. FHA release depends on its maturation by the specific B. pertussis protease SphB1. We constructed SphB1-deficient mutants and found that they were strongly affected in their ability to colonize the mouse respiratory tract, although they adhered even better to host cells in vitro than their wild-type parent strain. The defect in colonization could be overcome by prior nasal instillation of purified FHA or by coinfection with FHA-releasing B. pertussis strains, but not with SphB1-producing FHA-deficient strains, ruling out a nonspecific effect of SphB1. These results indicate that the release of FHA is important for colonization, as it may facilitate the dispersal of bacteria from microcolonies and the binding to new sites in the respiratory tract.

Fibronectin bound to the surface of Staphylococcus aureus induces association of very late antigen 5 and intracellular signaling factors with macrophage cytoskeleton

Staphylococcus aureus Cowan I and a clinically isolated coagulase-negative Staphylococcus strain, S. saprophyticus 10312, were found to have two fibronectin binding proteins, FnBPA and FnBPB. While both staphylococci bound to serum fibronectin to a similar extent, fibronectin binding significantly increased the phagocytic activity of macrophages against S. aureus (by ca. 150%) but not against S. saprophyticus. This enhancing effect of fibronectin was inhibited by an RGD sequence-containing peptide and also by anti-very late antigen 5 antibody. This suggests that the effect is mediated by very late antigen 5 expressed on macrophages. In macrophages ingesting fibronectin-bound Cowan I, alpha(5) and beta(1) chains were associated with the cytoskeleton. Cytosolic signaling factors such as paxillin, c-Src, and c-Csk were also associated with the cytoskeleton. On the contrary, beta(3) integrin transiently disappeared from the cytoskeleton when macrophages ingested the fibronectin-treated S. aureus Cowan I. Furthermore, the Src kinase family tyrosine kinase Lyn dissociated from the cytoskeleton. These cellular components did not respond in a fibronectin-dependent manner when macrophages phagocytosed S. saprophyticus. This means that only fibronectin-treated S. aureus Cowan I induces the accumulation of very late antigen 5, which in turn induces the association of paxillin and tyrosine kinases. It is thought that the phagocytic activity of macrophages against fibronectin-treated S. aureus was increased by signaling via the activation of very late antigen 5.

Helicobacter pylori interactions with host serum and extracellular matrix proteins: potential role in the infectious process

Helicobacter pylori, a gram-negative spiral-shaped bacterium, specifically colonizes the stomachs of humans. Once established in this harsh ecological niche, it remains there virtually for the entire life of the host. To date, numerous virulence factors responsible for gastric colonization, survival, and tissue damage have been described for this bacterium. Nevertheless, a critical feature of H. pylori is its ability to establish a long-lasting infection. In fact, although good humoral (against many bacterial proteins) and cellular responses are observed, most infected persons are unable to eradicate the infection. A large body of evidence has shown that the interaction between H. pylori and the host is very complex. In addition to the effect of virulence factors on colonization and persistence, binding of specialized bacterial proteins, known as receptins, to certain host molecules (ligands) could explain the success of H. pylori as a chronically persisting pathogen. Some of the reported interactions are of high affinity, as revealed by their calculated dissociation constant. This review examines the binding of host proteins (serum and extracellular matrix proteins) to H. pylori and considers the significance of these interactions in the infectious process. A more thorough understanding of the kinetics of these receptin interactions could provide a new approach to preventing deeper tissue invasion in H. pylori infections and could represent an alternative to antibiotic treatment.

Bacterial adhesion to sulcular epithelium in periodontitis

The purpose of this study was to investigate, by electron microscopy, the type of bacterial attachment to the sulcular epithelium in periodontitis. Gingiva biopsies were observed in a transmission electron microscope using cytochemical staining with ruthenium red for glycocalyx visualisation. In addition, subgingival plaque samples and biopsies from the sulcular epithelium in periodontitis from the patients were estimated microbiologically. Aerobic bacteria only were estimated in the subgingival plaque and both aerobic and anaerobic bacteria in the gingival biopsies. No bacterial internalisation could be observed. Fimbria-mediated adhesion as the only type of bacterial attachment and a large diversity of bacterial glycocalyces were detected. As the fimbrial adhesins of putative periodontal pathogens are able in vitro to induce inflammation and bone resorption via stimulation of the proinflammatory cytokine production, the demonstrated fimbrial adhesins suggest the significant role of bacterial adhesion to sulcular epithelium in periodontitis.

Isolation of an Escherichia coil strain mutant unable to form biofilm on polystyrene and to adhere to human pneumocyte cells: involvement of tryptophanase

Escherichia coli adherence to biotic and abiotic surfaces constitutes the first step of infection by promoting colonization and biofilm formation. The aim of this study was to gain a better understanding of the relationship between E. coli adherence to different biotic surfaces and biofilm formation on abiotic surfaces. We isolated mutants defective in A549 pneumocyte cells adherence, fibronectin adherence, and biofilm formation by random transposition mutagenesis and sequential passages over A549 cell monolayers. Among the 97 mutants tested, 80 were decreased in biofilm formation, 8 were decreased in A549 cells adherence, 7 were decreased in their adherence to fibronectin, and 17 had no perturbations in either of the three phenotypes. We observed a correlation between adherence to fibronectin or A549 cells and biofilm formation, indicating that biotic adhesive factors are involved in biofilm formation by E. coli. Molecular analysis of the mutants revealed that a transposon insertion in the tnaA gene encoding for tryptophanase was associated with a decrease in both A549 cells adherence and biofilm formation by E. coli. The complementation of the tnaA mutant with plasmid-located wild-type tnaA restored the tryptophanase activity, epithelial cells adherence, and biofilm formation on polystyrene. The possible mechanism of tryptophanase involvement in E. coli adherence and biofilm formation is discussed.

Fimbria-mediated bacterial adhesion to human oral epithelium

Oral mucosa biopsies and saliva samples from 12 individuals were processed for transmission (TEM) and scanning (SEM) electron microscopy with and without ruthenium red staining. Additionally performed microbiological estimations indicated in all bacteriological samples a facultative pathogenic flora. SEM and TEM investigation showed a diverse bacterial flora attached to the mucosal surface. Fimbriae comprising the glycocalyx and enabling bacterial attachment to the epithelial cells could be clearly visualised by ruthenium red. The only mode of bacterial attachment to the oral mucosa detected in the present investigation was fimbria-mediated adhesion and co-adhesion. The fimbria-mediated adhesion enables the bacterial persistence in the oral cavity and is the first step in the bacterial colonisation process.

Mucosal immunity in the lung and upper airway

The mucosal surfaces of the lungs and upper airways are common sites for infection. Extensive studies of the mechanisms associated with immune responses in the respiratory tract have found that understanding the system is challenging and involves many complex interactions to prevent and eliminate infection. Immune protection against diseases transmitted through the respiratory tract requires an understanding of the important aspects associated with beneficial, detrimental or ineffective immune responses. Two critical aspects of an immune response against a pathogen are that of the inductive stage, either induced by vaccination or primary infection, and the effector stage, the ability to recognise, respond to and eliminate the infection without detriment to the host. An immunisation strategy must not only have a measure of the induced antigen specific response, but this response must also be protective.

Probiotics: determinants of survival and growth in the gut

Bifidobacteria and lactobacilli are purportedly beneficial to human health and are called probiotics. Their survival during passage through the human gut, when administered in fermented milk products, has been investigated intensely in recent years. Well-controlled, small-scale studies on diarrhea in both adults and infants have shown that probiotics are beneficial and that they survive in sufficient numbers to affect gut microbial metabolism. Survival rates have been estimated at 20-40% for selected strains, the main obstacles to survival being gastric acidity and the action of bile salts. Although it is believed that the maximum probiotic effect can be achieved if the organisms adhere to intestinal mucosal cells, there is no evidence that exogenously administered probiotics do adhere to the mucosal cells. Instead, they seem to pass into the feces without having adhered or multiplied. Thus, to obtain a continuous exogenous probiotic effect, the probiotic culture must be ingested continually. Certain exogenously administered substances enhance the action of both exogenous and endogenous probiotics. Human milk contains many substances that stimulate the growth of bifidobacteria in vitro and also in the small intestine of infants; however, it is unlikely that they function in the colon. However, lactulose and certain fructose-containing compounds, called prebiotics, are not digested in the small intestine but pass into the cecum unchanged, where they are selectively utilized by probiotics. Beneficial effects may thus accrue from exogenously administered probiotics, often administered with prebiotics, or by endogenous bifidobacteria and lactobacilli, whose metabolic activity and growth may also be enhanced by the administration of prebiotics.

Attachment of Fusobacterium nucleatum PK1594 to mammalian cells and its coaggregation with periodontopathogenic bacteria are mediated by the same galactose-binding adhesin

It has been shown that Fusobacterium nucleatum PK1594 coaggregates with Prophyromonas gingivalis PK1924 through a galactose-binding adhesin. In the present study, attachment of F. nucleatum PK1594 to a variety of mammalian cells was characterized. F. nucleatum PK1594 attached to all eukaryotic cells tested, including human buccal epithelial cells, gingival and periodontal ligament fibroblasts, HeLa cells and murine lymphocytes, macrophages, and polymorphonuclear leukocytes. These attachments were (i) inhibited by galactose, lactose and N-acetylgalactosamine and (ii) inhibited by monoclonal antibody specific for the galactose-binding adhesin of F. nucleatum PK1594. In addition, a coaggregation-defective mutant of F. nucleatum PK1594 (PK2172), which does not exhibit galactose binding activity, did not attach to the mammalian cells. Coaggregation of F. nucleatum PK1594 with P. gingivalis PK 1924 and Actinobacillus actinomycetemcomitans JP2, but not with other bacteria, showed a similar pattern with sugars, monoclonal antibody, and the adhesin-deficient mutant. The results suggest that the attachment of F. nucleatum PK1594 to mammalian cells and its coaggregation with periodontal pathogens are mediated by the same galactose-binding adhesin.

Production and secretion of collagen-binding proteins from Aeromonas veronii

Collagen-binding protein (CNBP) synthesized by Aeromonas veronii is located conserved within the subcellular fraction. The results of this study show that 98% of the total CNBP produced by Aer. veronii is present in the extracellular medium, and that the remaining CNBP is distributed either on the cell surface, within the periplasm or anchored on the outer membrane. CNBP is specifically secreted from Aer. veronii into the culture medium, because all the beta-lactamase activity was located in the cells and could be released by polymixin B extraction of periplasmic proteins. CNBP was produced at growth temperatures from 12 degrees C to 42 degrees C, but not at 4 degrees C. The findings indicate that the level of CNBP in the medium increases during the exponential growth phase and reaches a maximum during the early stationary phase. There was less CNBP production in poor nutrient MMB medium than in the rich LB nutrient medium. CNBP secretion, in contrast to aerolysin secretion, was unaffected by the exeA mutation of Aer. hydrophila. It is concluded that CNBP secretion from Aer. veronii must be achieved by a mechanism different from that reported for aerolysin secretion.

Aggregation substance promotes adherence, phagocytosis, and intracellular survival of Enterococcus faecalis within human macrophages and suppresses respiratory burst

The aggregation substance (AS) of Enterococcus faecalis, encoded on sex pheromone plasmids, is a surface-bound glycoprotein that mediates aggregation between bacteria thereby facilitating plasmid transfer. Sequencing of the pAD1-encoded Asa1 revealed that this surface protein contains two RGD motifs which are known to ligate integrins. Therefore, we investigated the influence of AS on the interaction of E. faecalis with human monocyte-derived macrophages which constitutively express beta(2) integrins (e.g., CD18). AS was found to cause a greater-than-fivefold increase in enterococcal adherence to macrophages and a greater-than-sevenfold increase in phagocytosis. Adherence was mediated by an interaction between the RGD motif and the integrin CD11b/CD18 (complement receptor type 3) as demonstrated by inhibition studies with monoclonal antibodies and RGD peptide. AS-bearing enterococci were significantly more resistant to macrophage killing during the first 3 h postinfection, probably due to inhibition of the respiratory burst as indicated by reduced concentrations of superoxide anion.

Identification of type 4 fimbriae in Actinobacillus pleuropneumoniae

Type 4 fimbriae have been identified on the cell surface of Actinobacillus pleuropneumoniae by electron microscopy and N-terminal sequencing analysis. A. pleuropneumoniae type 4 fimbrial subunit protein, purified from cell cultures and from outer membrane preparations, reacted with polyclonal antibody raised against type 4 fimbriae of Moraxella bovis on Western blots. N-terminal sequence analysis of the purified 17 kDa type 4 fimbrial subunit protein, named ApfA, revealed the first 12 amino acids to be identical to those of other type 4 fimbrial subunit proteins.

Host cell invasion and intracellular residence by Aeromonas salmonicida: role of the S-layer

Virulent strains of the fish pathogen Aeromonas salmonicida, which have surface S-layers (S+), efficiently adhere to, enter, and survive within macrophages. Here we report that S+ bacteria were 10- to 20-fold more adherent to non-phagocytic fish cell lines than S-layer-negative (S-) mutants. When reconstituted with exogenous S-layers, these S- mutants regained adherence. As well, latex beads coated with purified S-layers were more adherent to fish cell lines than uncoated beads, or beads coated with disorganized S-layers, suggesting that purified S-layers were sufficient to mediate high levels of adherence, and that this process relied on S-layer structure. Gentamicin protection assays and electron microscopy indicated that both S+ and S- A. salmonicida invaded non-phagocytic fish cells. In addition, these fish cells were unable to internalize S-layer-coated beads, clearly suggesting that the S-layer is not an invasion factor. Lipopolysaccharide (which is partially exposed in S+ bacteria) appeared to mediate invasion. Surprisingly, A. salmonicida did not show net growth inside fish cells cultured in the presence of gentamicin, as determined by viable bacterial cell counts. On the contrary, bacterial viability sharply decreased after cell infection. We thus concluded that the S-layer is an adhesin that promotes but does not mediate invasion of non-phagocytic fish cell lines. These cell lines should prove useful in studies aimed at characterizing the invasion mechanisms of A. salmonicida, but of limited value in studying the intracellular residence and replication of this invasive bacterium in vitro.

How does Mycobacterium leprae target the peripheral nervous system?

Mycobacterium leprae has the capacity to invade the peripheral nervous system and cause neuropathy. The molecular mechanisms responsible have remained unknown until recently. Identification of the endoneurial laminin-2 isoform and its receptor alpha-dystroglycan as neural targets of M. leprae has not only opened up a new area of scientific inquiry into the pathogenesis of neurological damage in leprosy, but has also revealed unexpected biological properties of these important host molecules.

Distribution and antigenicity of fibronectin binding proteins (SfbI and SfbII) of Streptococcus pyogenes clinical isolates from the northern territory, Australia

Fibronectin binding proteins play an important role in the adherence and invasion of group A streptococci (GAS). Genotypically distinct GAS isolates were screened for the presence and expression of two streptococcal fibronectin binding protein genes, sfbI and sfbII. Of the tested strains, 64 and 36% were shown to harbor and express the sfbI and sfbII genes, respectively. All sfbII-positive strains tested were also positive for sfbI, but only 28% of the sfbII-negative strains were positive for sfbI. High levels of immunoglobulin G antibodies to both SfbI and SfbII were found in sera from 80 subjects with defined streptococcal infections.

SIgA- and IgG-coated Streptococcus pyogenes on the tonsillar surfaces during acute tonsillitis

Bacterial swabs were collected from the tonsillar surfaces of eight patients with current acute tonsillitis, culture-positive for Streptococcus pyogenes. Using gold-labelled antiserum to S. pyogenes, these micro-organisms could be localized in the samples by transmission electron microscopy. S. pyogenes pathogens were further characterized with gold-labelled antiserum to human IgG and SIgA antibodies. Roughly 90% of the pathogens were found coated with IgG antibodies, irrespective of the duration of the disease, whereas the proportion of SIgA-coated pathogens increased with disease duration. Insufficient IgA coating of pathogens might well be a contributory cause of the induction of tonsillar infection, probably due to inadequate prevention of the attachment of the S. pyogenes bacteria to the tonsillar surface epithelium.

Enterococcus faecalis bearing aggregation substance is resistant to killing by human neutrophils despite phagocytosis and neutrophil activation

Enterococcus faecalis aggregation substance (AS) mediates efficient bacterium-bacterium contact to facilitate plasmid exchange as part of a bacterial sex pheromone system. We have previously determined that AS promotes direct, opsonin-independent binding of E. faecalis to human neutrophils (PMNs) via complement receptor type 3 and other receptors on the PMN surface. We have now examined the functional consequences of this bacterium-host cell interaction. AS-bearing E. faecalis was phagocytosed and internalized by PMNs, as determined by deconvolution fluorescence microscopy. However, these bacteria were not killed by PMNs, and internalized bacteria excluded propidium iodide, indicating intact bacterial membranes. Resistance to killing occurred despite activation of PMNs, as indicated by an increase in both functional and total surface Mac-1 expression, shedding of L-selectin, and an increase in PMN extracellular superoxide and phagosomal oxidant production. Deconvolution fluorescence microscopy also revealed that phagosomes containing AS-bearing bacteria were markedly larger than phagosomes containing opsonized E. faecalis, suggesting that some modification of phagosomal maturation may be involved in AS-induced resistance to killing. PMN phagosomal pH was significantly higher after ingestion of nonopsonized AS-bearing E. faecalis than after that of opsonized bacteria. The novel ability of AS to promote intracellular survival of E. faecalis inside PMNs suggests that AS may be a virulence factor used by strains of E. faecalis.

Where are the receptors for Streptococcus pyogenes located on the tonsillar surface epithelium?

Streptococcus pyogenes is the most frequent causative agent of acute pharyngotonsillitis (AT). The first events in the etiopathogenesis of an AT infection caused by these bacterial pathogens are their penetration through the mucus film covering the oropharyngeal mucosa, and their attachment to the surface epithelium. Adherence of S. pyogenes to tonsillar epithelial cells is a precondition for bacterial colonisation, for triggering off cell activation, internalising of bacteria into the epithelial cells and cytokine release from the epithelial cells with subsequent induction of an inflammatory reaction in underlying tissues. Scanning and transmission electron microscopic studies revealed that the surface epithelium of the human palatine tonsils consisted of a weakly keratinized, stratified squamous epithelium built up of pentangular cells where the apical cell surface formed an irregular pattern of microridges. The distance between two adjacent microridges was roughly one-third of the diameter of a S. pyogenes bacterium. By using gold-labelled antiserum to S. pyogenes, we showed that the target region for these pathogens on the epithelial cells during an on-going AT infection was located on the crests of the microridges where bacterial pili made adhesin-receptor contact with the tonsillar surface epithelium.

Enterococcus faecalis aggregation substance promotes opsonin-independent binding to human neutrophils via a complement receptor type 3-mediated mechanism

Enterococcus faecalis aggregation substance (AS) mediates efficient adhesion between bacteria, thereby facilitating plasmid exchange as an integral part of a bacterial sex pheromone system. We examined the interaction of AS-bearing E. faecalis with human neutrophils (PMNs), an important component of the host defense system. AS promoted a markedly increased opsonin-independent bacterial binding to PMNs. Adhesion was dependent on the expression of the enterococcal Asc10 protein, which contains two Arg-Gly-Asp (RGD) sequences, and addition of exogenous RGD-containing peptides inhibited AS-mediated binding by 66%. AS-mediated adhesion was inhibited by 85% by anti-human complement receptor type 3 (CR3) monoclonal antibodies or by use of PMNs from a patient with leukocyte adhesion deficiency. However, AS-bearing E. faecalis cells were unable to bind to CHO-Mac-1 cells, expressing functionally active CR3, suggesting the potential need for additional PMN surface receptors for bacterial adhesion. Monoclonal antibodies against integrin-associated protein (CD47) and L-selectin, both of which may interact with CR3 and bind to ligands on E. faecalis, also inhibited AS-dependent binding. The non-opsonic binding of E. faecalis to PMNs may play an important role in this organism's pathogenesis.

Porins and lipopolysaccharide (LPS) from Salmonella typhimurium induce leucocyte transmigration through human endothelial cells in vitro

Bacteria or bacterial products may constitute important inducers of surface molecule expression on endothelial cells and leucocytes. This study was undertaken to determine the effects of the Salmonella typhimurium porins, LPS-S and LPS-R on the transendothelial migration of leucocytes through human umbilical vein endothelial cells (HUVEC). Treatment of the HUVEC with either porins or LPS-S or LPS-R increased the transmigration of different leucocyte populations, in particular that of neutrophils. The maximal increase occurred using LPS-S treatment, whereas porin stimulation fell between LPS-S and LPS-R. The transmigration increase was dose-dependent and reached its maximum at about 100-1000 ng/ml of stimulus. Optimal endothelial activation occurred after 2-4 h and 4-6 h using LPS and porin, respectively. Stimulation of leucocytes with either porins or LPS slightly increased their transmigration through non-activated endothelial cells. Transmigration increased remarkably during the simultaneous stimulation of endothelial cells by IL-1ss together with either porins or LPS. To assess participation of E-selectin, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and leucocyte adhesion complex (CD11/18) in porin- or LPS-mediated leucocyte migration, blocking MoAbs were used. Each blocking MoAb partially and selectively decreased leucocyte transmigration. The obtained results contribute to clarify some aspects of the inflammatory process at sites of infection.

Type IV pili of pathogenic Neisseriae elicit cortical plaque formation in epithelial cells

The pathogenic Neisseriae Neisseria meningitidis and Neisseria gonorrhoeae, initiate colonization by attaching to host cells using type IV pili. Subsequent adhesive interactions are mediated through the binding of other bacterial adhesins, in particular the Opa family of outer membrane proteins. Here, we have shown that pilus-mediated adhesion to host cells by either meningococci or gonococci triggers the rapid, localized formation of dramatic cortical plaques in host epithelial cells. Cortical plaques are enriched in both components of the cortical cytoskeleton and a subset of integral membrane proteins. These include: CD44v3, a heparan sulphate proteoglycan that may serve as an Opa receptor; EGFR, a receptor tyrosine kinase; CD44 and ICAM-1, adhesion molecules known to mediate inflammatory responses; f-actin; and ezrin, a component that tethers membrane components to the actin cytoskeleton. Genetic analyses reveal that cortical plaque formation is highly adhesin specific. Both pilE and pilC null mutants fail to induce cortical plaques, indicating that neisserial type IV pili are required for cortical plaque induction. Mutations in pilT, a gene required for pilus-mediated twitching motility, confer a partial defect in cortical plaque formation. In contrast to type IV pili, many other neisserial surface structures are not involved in cortical plaque induction, including Opa, Opc, glycolipid GgO4-binding adhesins, polysialic acid capsule or a particular lipooligosaccharide variant. Furthermore, it is shown that type IV pili allow gonococci to overcome the inhibitory effect of heparin, a soluble receptor analogue, on gonococcal invasion of Chang and A431 epithelial cells. These and other observations strongly suggest that type IV pili play an active role in initiating neisserial infection of the mucosal surface in vivo. The functions of type IV pili and other neisserial adhesins are discussed in the specific context of the mucosal microenvironment, and a multistep model for neisserial colonization of mucosal epithelia is proposed.

Isolation of a laminin-binding protein from the protozoan parasite Leishmania donovani that may mediate cell adhesion

Extracellular matrix (ECM)-binding proteins on the surface of Leishmania are thought to play a crucial role in the onset of leishmaniasis, as these parasites invade mononuclear phagocytes in various organs after migrating through the ECM. In a previous report, we presented several lines of evidence suggesting that Leishmania has a specific receptor for laminin, a major ECM protein, with a Kd in the nanomolar range. Here we describe the identification, purification and biochemical characterization of the Leishmania laminin receptor. When the outer membrane proteins of L. donovani were blotted on to nitrocellulose paper and probed with laminin, a prominent laminin-binding protein of 67 kDa was identified. The purified protein was isolated by a three-step process involving DEAE-cellulose, Con A (concanavalin A)-Sepharose and laminin-Sepharose affinity chromatography and was used to raise a monospecific antibody. The same protein was obtained when parasite membrane extracts were adsorbed to antibody affinity matrix and eluted with glycine. The affinity-purified protein bound to laminin in a detergent-solubilized form as well as after integration into artificial bilayers, and was subsequently characterized as an integral membrane protein. Metaperiodate oxidation and metabolic inhibition of glycosylation studies indicate the binding protein to be glycoprotein in nature and that N-linked oligosaccharides play a part in the interaction of laminin with the binding protein. Surface-labelled parasites attached to microtitre wells coated with laminin and the 67 kDa protein blocked the adhesion to laminin substrate. We propose that the 67 kDa protein is an adhesin involved in the attachment of Leishmania to host tissues.

Adhesins as targets for vaccine development

Blocking the primary stages of infection, namely bacterial attachment to host cell receptors and colonization of the mucosal surface, may be the most effective strategy to prevent bacterial infections. Bacterial attachment usually involves an interaction between a bacterial surface protein called an adhesin and the host cell receptor. Recent preclinical vaccine studies with the FimH adhesin (derived from uropathogenic Escherichia coli) have confirmed that antibodies elicited against an adhesin can impede colonization, block infection, and prevent disease. The studies indicate that prophylactic vaccination with adhesins can block bacterial infections. With recent advances in the identification, characterization, and isolation of other adhesins, similar approaches are being explored to prevent infections, from otitis media and dental caries to pneumonia and sepsis.

Interaction of the Fungal Pathogen Candida albicans with Integrin CD11b/CD18: Recognition by the I Domain Is Modulated by the Lectin-Like Domain and the CD18 Subunit

Interactions of microorganisms with integrins are central to the host defense mechanisms. The leukocyte integrin CD11b/CD18 is the principal adhesion receptor on leukocytes for Candida albicans, a major opportunistic pathogen. In this study we have investigated the roles of three regions within the receptor, the inserted (I) and lectin-like domains within the CD11b subunit, and the CD18 subunit, in CD11b/CD18-C. albicans interactions. We report four major findings. 1) A mutation in CD18 exerts a dominant negative effect on the function of the CD11b/CD18 complex. This interpretation is based on the observation that in the absence of CD18, the CD11b subunit alone binds C. albicans well, but a single point mutation at Ser138 of CD18 abolishes CD11b/CD18 binding of the fungus. 2) The lectin-like domain is not sufficient for CD11b/CD18-C. albicans interactions. Rather, the lectin-like domain appears to influence CD11b/CD18 binding activity by modulating the function of the I domain. 3) The I domain is the primary binding site for C. albicans in the receptor and is sufficient to support an efficient interaction. 4) We have identified specific amino acid sequences within the I domain that engage the microorganism. Compared with other ligands of CD11b/CD18, C. albicans has some unique as well as common contact sites within the I domain of the receptor. Such unique contact sites may underlie the ability of C. albicans to modulate CD11b/CD18 function and raise the possibility for selective interference of the microorganism-host leukocyte interactions.

Oligosaccharide receptors for bacteria: a view to a kill

Oligosaccharide recognition is a major means of bacterial-host cell attachment. Bacterial-host receptor binding can subvert host signaling pathways to cause pathology. In addition, pathogenic bacteria can utilize more than one recognition system to bind host cells. Recent studies of Helicobacter pylori illustrate both these points. Together with this redundancy in recognition, the importance of multivalent sugar binding has become apparent. Multivalent sugar receptor analogs have been used to both prevent and detach adherent bacteria. Several new chemical technologies for the generation of bioactive glycopolymers have been developed and may be successfully adapted to address both these issues.

Haemophilus ducreyi secretes a filamentous hemagglutinin-like protein

We have identified two extremely large open reading frames (ORFs) in Haemophilus ducreyi 35000, lspA1 and lspA2, each of which encodes a predicted protein product whose N-terminal half is approximately 43% similar to the N-terminal half of Bordetella pertussis filamentous hemagglutinin (FhaB). To the best of our knowledge, lspA1 (12,500 nucleotides [nt]) and lspA2 (14,800 nt) are among the largest prokaryotic ORFs identified to date. The predicted proteins, LspA1 and LspA2, are 86% identical overall to each other and also have limited amino acid sequence similarity at their N termini to other secreted bacterial proteins, including certain hemolysins. Southern blot analysis indicated that lspA1 and lspA2 sequences were present in 15 other geographically diverse H. ducreyi strains. Reverse transcriptase PCR analysis of total RNA isolated from H. ducreyi 35000 grown in liquid medium, grown on solid agar medium, and isolated from lesions of H. ducreyi-infected rabbits indicated that lspA1 and lspA2 were transcribed both in vitro and in vivo. A 260-kDa protein present in culture supernatant from eight virulent H. ducreyi strains reacted with both polyclonal serum from rabbits infected with H. ducreyi 35000 and a monoclonal antibody predicted to bind both LspA1 and LspA2. This 260-kDa protein in H. ducreyi 35000 culture supernatant was shown to be the protein product of the lspA1 ORF based on its reactivity with a monoclonal antibody specific for LspA1. Four H. ducreyi strains, previously shown to be avirulent in the temperature-dependent rabbit model for chancroid, did not produce either LspA1 or LspA2 in vitro. This finding raised the possibility that LspA1, LspA2, or both may be involved in the ability of H. ducreyi to cause lesions in this animal model.

In vitro inhibition of epithelial cell invasion by Aeromonashydrophila Vibrio species by fish Aeromonas hydrophila major adhesin

A virulent strain of Aeromonas hydrophila (PPD 134/91) was obtained from the Primary Production Department, Singapore. Its major adhesin was isolated and purified by potassium thiocyanate extraction and Bio-Gel P-100 gel filtration. The ability of the protein in peak 1, termed major adhesin, to inhibit bacteria from adhering to and invading host cells was studied in vitro using epithelioma papillosum cells of carp (EPC). Results showed that a concentration of 10 μg ml^-1 of this major adhesin could competitively inhibit 28% of A. hydrophila PPD 134/91 from invading EPC cells in vitro. When the concentration was increased to 40 μg ml^-1 , the major adhesin significantly cross-inhibited nine other virulent or weakly virulent strains of A. hydrophila. In addition, the major adhesin significantly inhibited not only another bacterial strain from the same family, Aeromonas sobria, but also strains of Vibrio spp. tested. Therefore, we suggest that the major adhesin of this virulent A. hydrophila strain has the potential to be used as a vaccine against the heterogeneous Aeromonas and Vibrio species.

Surface ultrastructure of intact and in situ chlorhexidine-treated human buccal cells. A method for scanning electron microscopy

Air-dried and ethanol-fixed buccal epithelial cell smears from five subjects were observed by scanning electron microscopy. The mucous pellicle was precipitated as a smooth haze covering the cells, and outlines of bacteria were found embedded within it. Rinsing the preparations under running water gradually diminished the mucous pellicle but not the cell-adherent bacteria. A more complete dissolution of the pellicle was accomplished by washing the buccal epithelial cells before smearing. After a chlorhexidine mouthrinse the buccal cells appeared distorted, with only a few adherent bacteria. Three days after the rinsing, the denatured appearance still persisted on many cells, however, simultaneously with the emergence of undenatured epithelial cells with adherent bacteria. The method introduced in this study is useful to investigate the bacteria-mucus-epithelial cell interactions. A possible mode of antibacterial activity of chlorhexidine in vivo may be that it destroys bacterial adhesins. The substantivity of chlorhexidine in the oral cavity may be linked to the turnover rate of the oral epithelial cells.

Attachment of piliated, Opa- and Opc- gonococci and meningococci to epithelial cells elicits cortical actin rearrangements and clustering of tyrosine-phosphorylated proteins

Attachment of piliated Neisseria gonorrhoeae or Neisseria meningitidis cells to A431, Chang, HEC-1-B, or polarized T(84) cells triggers rearrangements of cortical microfilaments and the accumulation of phosphotyrosine-containing proteins at sites of bacterial contact. Actin stress fibers and the microtubule network remain unaltered in infected cells. The rearrangements reported here are triggered by piliated, Opa- and Opc- strains and also by nonpiliated gonococci (GC) that produce the invasion-associated OpaA protein. Thus, neisserial adhesion via either of at least two different adhesins can trigger cortical rearrangements. In contrast, these rearrangements are not triggered by nonadherent GC or meningococcal strains, by heat-killed or chloramphenicol-treated GC strains, or by Escherichia coli recombinants that adhere to cells via GC OpaA or Opal fusion proteins, suggesting that additional neisserial components are involved. Immunoblotting experiments did not detect consistent increases in the phosphorylation of specific proteins. Possible biological implications of these Neisseria-induced cortical rearrangements are discussed.