Role of de-N-acetylase PgaB from Aggregatibacter actinomycetemcomitans in exopolysaccharide export in biofilm mode of growth

Aggregatibacter actinomycetemcomitans, a Gram-negative bacterium, is the causative agent of localized aggressive periodontitis. Attachment to a biotic surface is a critical first step in the A. actinomycetemcomitans infection process for which exopolysaccharides have been shown to be essential. In addition, the pga operon, containing genes encoding for biosynthetic proteins for poly-N-acetyl glucosamine (PNAG), plays a key role in A. actinomycetemcomitans virulence, as a mutant strain lacking the pga operon induces significantly less bone resorption. Among the genes in the pga operon, pgaB codes for a de-N-acetylase that is responsible for the deacetylation of the PNAG exopolysaccharide. Here we report the role of PgaB in regulation of virulence genes using a markerless, scarless deletion mutant targeting the coding region of the N-terminal catalytic domain of PgaB. The results demonstrate that the N-terminal, catalytic domain of PgaB is crucial for exopolysaccharide export.

Theranostic body fluid cleansing: rationally designed magnetic particles enable capturing and detection of bacterial pathogens

We show theoretical and experimental considerations on bacteria capturing and enrichment via magnetic separation enabling integrated diagnosis and treatment of blood stream infections.

Pleiotropic effects of the lpxM mutation in Yersinia pestis resulting in modification of the biosynthesis of major immunoreactive antigens

Deletion mutants in the lpxM gene in two Yersinia pestis strains, the live Russian vaccine strain EV NIIEG and a fully virulent strain, 231, synthesise a less toxic penta-acylated lipopolysaccharide (LPS). Analysis of these mutants revealed they possessed marked reductions in expression and immunoreactivity of numerous major proteins and carbohydrate antigens, including F1, Pla, Ymt, V antigen, LPS, and ECA. Moreover, both mutants demonstrated altered epitope specificities of the antigens as determined in immunodot-ELISAs and immunoblotting analyses using a panel of monoclonal antibodies. The strains also differed in their susceptibility to the diagnostic plague bacteriophage L-413C. These findings indicate that the effects of the lpxM mutation on reduced virulence and enhanced immunity of the Y. pestis EV DeltalpxM is also associated with these pleiotropic changes and not just to changes in the lipid A acylation.

Protection from Staphylococcus aureus mastitis associated with poly-N-acetyl beta-1,6 glucosamine specific antibody production using biofilm-embedded bacteria

Staphylococcus aureus vaccines based on bacterins surrounded by slime, surface polysaccharides coupled to protein carriers and polysaccharides embedded in liposomes administered together with non-biofilm bacterins confer protection against mastitis. However, it remains unknown whether protective antibodies are directed to slime-associated known exopolysaccharides and could be produced in the absence of bacterin immunizations. Here, a sheep mastitis vaccination study was carried out using bacterins, crude bacterial extracts or a purified exopolysaccharide from biofilm bacteria delivered in different vehicles. This polysaccharide reacted specifically with antibodies to poly-N-acetyl-beta-1,6-glucosamine (PNAG) and not with antibodies to other capsular antigens or bacterial components. Following intra-mammary challenge with biofilm-producing bacteria, antibody production against the polysaccharide, milk bacterial counts and mastitis lesions were determined. Bacterins from strong biofilm-producing bacteria triggered the highest production of antibodies to PNAG and conferred the highest protection against infection and mastitis, compared with weak biofilm-producing bacteria and non-cellular inocula. Thus, bacterins from strong biofilm bacteria, rather than purified polysaccharide, are proposed as a cost-efficient vaccination against S. aureus ruminant mastitis.

A Yersinia pestis lpxM-mutant live vaccine induces enhanced immunity against bubonic plague in mice and guinea pigs

The lpxM mutant of the live vaccine Yersinia pestis EV NIIEG strain synthesising a less toxic penta-acylated lipopolysaccharide was found to be avirulent in mice and guinea pigs, notably showing no measurable virulence in Balb/c mice which do retain some susceptibility to the parental strain itself. Twenty-one days after a single injection of the lpxM-mutant, 85-100% protection was achieved in outbred mice and guinea pigs, whereas a 43% protection rate was achieved in Balb/c mice given single low doses (10(3) to 2.5 x 10(4) CFU) of this vaccine. A subcutaneous challenge with 2000 median lethal doses (equal to 20,000 CFU) of fully virulent Y. pestis 231 strain, is a 6-10-fold higher dose than that which the EV NIIEG itself can protect against.

The study of the reaction of terminated oligomerization in the synthesis of oligo-(β1-6)-glucosamines

The applicability of terminated oligomerization to the synthesis of oligo-(beta1-6)-glycosamines, fragments of the intercellular polysaccharide adhesin of staphylococci, was studied. The reactions of terminated oligomerization were carried out with mono-, di-, and trisaccharide monomers and N-protected aminopropanol; and spacered mono- and disaccharides as terminating molecules were also attempted. The primary formation of cyclic products of monomer intramolecular glycosylation was observed in almost all the reactions. Only the experiments with the monomer based on the disaccharide bromide under the conditions of the Helferich reaction led to reduced yields (30%) of the cyclic products. However, even in this case, the desired terminated oligosaccharides were generated in approximately 10% yield and mainly were the products of single glycosylation of the terminator by the monomer. These experiments allow the conclusion that, under the examined conditions, the reaction of terminated oligomerization could not result in the synthesis of oligoglucosamines with a high molecular mass.

Full structure of the lipopolysaccharide of Pseudomonas aeruginosa immunotype 5

The lipopolysaccharide (LPS) of the opportunistic human pathogen Pseudomonas aeruginosa immunotype 5 was delipidated by mild acid hydrolysis, and the products were separated by high-performance anion-exchange chromatography and analyzed by ESI MS and NMR spectroscopy. LPS species of three types were found, including those with an unsubstituted core and the core substituted with one O-polysaccharide repeating unit or with an O-polysaccharide of a variable number of repeating units. The core region is highly phosphorylated, the major species containing two monophosphate groups and one ethanolamine diphosphate group. Based on these and published data on the O-polysaccharide structure, the full structure of the LPS of P. aeruginosa immunotype 5 was established.

Elucidation of the structure of the lipopolysaccharide core and the linkage between the core and the O-antigen in Pseudomonas aeruginosa immunotype 5 using strong alkaline degradation of the lipopolysaccharide

The products of the strong alkaline degradation of the lipopolysaccharide (LPS) of Pseudomonas aeruginosa immunotype 5 were separated by anion-exchange HPLC and studied by electrospray ionization mass spectrometry and NMR spectroscopy. It was found that two major products have the same inner core region and lipid A carbohydrate backbone (A) but different outer core regions (B and C). The difference is in the position of a rhamnose residue, which is substituted with either an additional glucose residue (B) or a disaccharide remainder of the degraded O-polysaccharide (C). The site and the configuration of the linkage between the O-polysaccharide and the core were determined and, together with published data, the structure of the so-called biological repeating unit of the O-antigen was defined (D). The glycosidic linkage of the quinovosamine residue is beta when it links the O-polysaccharide to the core (C) and alpha when it connects the interior repeating units of the O-polysaccharide to each other (D) [Formula: see text]. In the structures shown Rha stands for rhamnose, Kdo for 3-deoxy-D-manno-oct-2-ulosonic acid, Hep for L-glycero-D-manno-heptose, GalNAcA for 2-acetamido-2-deoxygalacturonic acid, QuiN for 2-amino-2,6-dideoxyglucose (quinovosamine), DeltaHexNA for 2-amino-2-deoxy-D-threo-hex-4-enuronic acid; all monosaccharides are in the pyranose form and have the D configuration, except for Rha and GalNAcA that have the L configuration. In C, the remainder of the degraded O-polysaccharide is shown in bold type.

Epithelial cell contact-induced alterations in Salmonella enterica serovar Typhi lipopolysaccharide are critical for bacterial internalization

The invasion of Pseudomonas aeruginosa and Salmonella enterica serovar Typhi into epithelial cells depends on the cystic fibrosis transmembrane conductance regulator (CFTR) protein as an epithelial receptor. In the case of P. aeruginosa, the bacterial ligand for CFTR is the outer core oligosaccharide portion of the lipopolysaccharide (LPS). To determine whether serovar Typhi LPS is also a bacterial ligand mediating internalization, we used both P. aeruginosa and serovar Typhi LPS as a competitive inhibitor of serovar Typhi invasion into the epithelial cell line T84. P. aeruginosa LPS containing a complete core efficiently inhibited serovar Typhi invasion. However, neither killed wild-type Typhi cells nor purified LPS were effective inhibitors. LPS from mutant Typhi strains defective in O side-chain synthesis, but with an apparently normal core, was capable of inhibiting invasion, but LPS obtained from a deeper rough mutant strain with alterations in fast-migrating core oligosaccharide failed to inhibit invasion. Lastly, exposure of wild-type serovar Typhi to T84 cultures before heat killing resulted in a structural alteration in its LPS that allowed the heat-killed cells to inhibit invasion of wild-type serovar Typhi. These data indicate that the serovar Typhi LPS core, like the P. aeruginosa LPS core, is a ligand mediating internalization of bacteria by epithelial cells, and that exposure of this ligand on wild-type Typhi is induced by the bacteria's interaction with host cells.

Structural analysis of the lipopolysaccharide core of a rough, cystic fibrosis isolate of Pseudomonas aeruginosa

Lipopolysaccharide (LPS) expressed by isolates of Pseudomonas aeruginosa from cystic fibrosis patients lacks the O-polysaccharide chain but the degree to which the rest of the molecule changes has not been determined. We analyzed, for the first time, the core structure of an LPS from a rough, cystic fibrosis isolate of P. aeruginosa. The products of mild acid hydrolysis and strong alkaline degradation of the LPS were studied by ESI MS, MALDI MS, and NMR spectroscopy. The following structure was determined for the highest-phosphorylated core-lipid A backbone oligosaccharide isolated after alkaline deacylation of the LPS: [structure: see text] where Kdo and Hep are 3-deoxy-D-manno-octulosonic acid and L-glycero-D-manno-heptose, respectively; all sugars are in the pyranose form and have the D configuration unless stated otherwise. The outer core region occurs as two isomeric glycoforms differing in the position of rhamnose (Rha). The inner core region carries four phosphorylation sites at two Hep residues, HepI being predominantly bisphosphorylated and HepII monophosphorylated. In the intact LPS, both Hep residues carry monophosphate and diphosphate groups in nonstoichiometric quantities, GalN is N-acylated by an L-alanyl group, HepII is 7-O-carbamoylated, and the outer core region is nonstoichiometrically O-acetylated at four sites. Therefore, the switch to the LPS-rough phenotype in cystic fibrosis isolates of P. aeruginosa is not accompanied by losses of core monosaccharide, phosphate or acyl components. The exact positions of the O-acetyl groups and the role of the previously undescribed O-acetylation in the LPS core of P. aeruginosa remain to be determined.

Transgenic cystic fibrosis mice exhibit reduced early clearance of Pseudomonas aeruginosa from the respiratory tract

The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) has been proposed to be an epithelial cell receptor for Pseudomonas aeruginosa involved in bacterial internalization and clearance from the lung. We evaluated the role of CFTR in clearing P. aeruginosa from the respiratory tract using transgenic CF mice that carried either the DeltaF508 Cftr allele or an allele with a Cftr stop codon (S489X). Intranasal application achieved P. aeruginosa lung infection in inbred C57BL/6 DeltaF508 Cftr mice, whereas DeltaF508 Cftr and S489X Cftr outbred mice required tracheal application of the inoculum to establish lung infection. CF mice showed significantly less ingestion of LPS-smooth P. aeruginosa by lung cells and significantly greater bacterial lung burdens 4.5 h postinfection than C57BL/6 wild-type mice. Microscopy of infected mouse and rhesus monkey tracheas clearly demonstrated ingestion of P. aeruginosa by epithelial cells in wild-type animals, mostly around injured areas of the epithelium. Desquamating cells loaded with P. aeruginosa could also be seen in these tissues. No difference was found between CF and wild-type mice challenged with an LPS-rough mucoid isolate of P. aeruginosa lacking the CFTR ligand. Thus, transgenic CF mice exhibit decreased clearance of P. aeruginosa and increased bacterial burdens in the lung, substantiating a key role for CFTR-mediated bacterial ingestion in lung clearance of P. aeruginosa.

Exploitation of syndecan-1 shedding by Pseudomonas aeruginosa enhances virulence

Cell-surface heparan sulphate proteoglycans (HSPGs) are ubiquitous and abundant receptors/co-receptors of extracellular ligands, including many microbes. Their role in microbial infections is poorly defined, however, because no cell-surface HSPG has been clearly connected to the pathogenesis of a particular microbe. We have previously shown that Pseudomonas aeruginosa, through its virulence factor LasA, enhances the in vitro shedding of syndecan-1-the predominant cell-surface HSPG of epithelia. Here we show that shedding of syndecan-1 is also activated by P. aeruginosa in vivo, and that the resulting syndecan-1 ectodomains enhance bacterial virulence in newborn mice. Newborn mice deficient in syndecan-1 resist P. aeruginosa lung infection but become susceptible when given purified syndecan-1 ectodomains or heparin, but not when given ectodomain core protein, indicating that the ectodomain's heparan sulphate chains are the effectors. In wild-type newborn mice, inhibition of syndecan-1 shedding or inactivation of the shed ectodomain's heparan sulphate chains prevents lung infection. Our findings uncover a pathogenetic mechanism in which a host response to tissue injury-syndecan-1 shedding-is exploited to enhance microbial virulence apparently by modulating host defences.

Role of alginate O acetylation in resistance of mucoid Pseudomonas aeruginosa to opsonic phagocytosis

Establishment and maintenance of chronic lung infections with mucoid Pseudomonas aeruginosa in patients with cystic fibrosis (CF) require that the bacteria avoid host defenses. Elaboration of the extracellular, O-acetylated mucoid exopolysaccharide, or alginate, is a major microbial factor in resistance to immune effectors. Here we show that O acetylation of alginate maximizes the resistance of mucoid P. aeruginosa to antibody-independent opsonic killing and is the molecular basis for the resistance of mucoid P. aeruginosa to normally nonopsonic but alginate-specific antibodies found in normal human sera and sera of infected CF patients. O acetylation of alginate appears to be critical for P. aeruginosa resistance to host immune effectors in CF patients.

Lack of adherence of clinical isolates of Pseudomonas aeruginosa to asialo-GM(1) on epithelial cells

Numerous studies have reported that asialo-GM(1), gangliotetraosylceramide, or moieties serve as epithelial cell receptors for Pseudomonas aeruginosa. Usually this interaction is confirmed with antibodies to asialo-GM(1). However, few, if any, of these reports have evaluated the binding of fresh clinical isolates of P. aeruginosa to asialo-GM(1) or the specificity of the antibodies for the asialo-GM(1) antigen. We confirmed that asialo-GM(1) dissolved in dimethyl sulfoxide could be added to the apical membrane of Madin-Darby canine kidney cells growing as a polarized epithelium on Transwell membranes (J. C. Comolli, L. L. Waite, K. E. Mostov, and J. N. Engel, Infect. Immun. 67:3207-3214, 1999) and that such treatment enhanced the binding of P. aeruginosa strain PA103. However, no other P. aeruginosa strain, including eight different clinical isolates, exhibited enhanced binding to asialo-GM(1)-treated cells. Studies with commercially available antibodies to asialo-GM(1) showed that these preparations had high titers of antibody to P. aeruginosa antigens, including whole cells, purified lipopolysaccharide (LPS), and pili. Inhibition studies showed that adsorption of an antiserum to asialo-GM(1) with P. aeruginosa cells could remove the reactivity of antibodies to asialo-GM(1), and adsorption of this serum with asialo-GM(1) removed antibody binding to P. aeruginosa LPS. Antibodies in sera raised to asialo-GM(1) were observed to bind to P. aeruginosa cells by immunoelectron microscopy. Antibodies to asialo-GM(1) inhibited formation of a biofilm by P. aeruginosa in the absence of mammalian cells, indicating a direct inhibition of bacterial cell-cell interactions. These findings demonstrate that asialo-GM(1) is not a major cellular receptor for clinical isolates of P. aeruginosa and that commercially available antibodies raised to this antigen contain high titers of antibody to multiple P. aeruginosa antigens, which do not interfere with the binding of P. aeruginosa to mammalian cells but possibly interfere with the binding of P. aeruginosa cells to each other.

The role of the CFTR in susceptibility to Pseudomonas aeruginosa infections in cystic fibrosis

Recent molecular and cellular studies have shed new light on the basis for the susceptibility of cystic fibrosis (CF) patients to Pseudomonas aeruginosa infection. Changes in airway liquid composition and/or viscosity, enhanced bacterial binding to mucin and epithelial cell receptors, increased innate inflammation owing to disruptions in lipid metabolism and a role for the CFTR protein in bacterial ingestion and clearance have all been postulated. The high P. aeruginosa infection rate in CF patients can potentially be explained by the specificity of the interaction between the CFTR and P. aeruginosa.

Vaccine potential of poly-1-6 beta-D-N-succinylglucosamine, an immunoprotective surface polysaccharide of Staphylococcus aureus and Staphylococcus epidermidis

Staphylococcus aureus and S. epidermidis are among the most common causes of nosocomial infection, and S. aureus is also of major concern to human health due to its occurrence in community-acquired infections. These staphylococcal species are also major pathogens for domesticated animals. We have previously identified poly-N-succinyl beta-1-6 glucosamine (PNSG) as the chemical form of the S. epidermidis capsular polysaccharide/adhesin (PS/A) which mediates adherence of coagulase-negative staphylococci (CoNS) to biomaterials, serves as the capsule for strains of CoNS that express PS/A, and is a target for protective antibodies. We have recently found that PNSG is made by S. aureus as well, where it is an environmentally regulated, in vivo-expressed surface polysaccharide and similarly serves as a target for protective immunity. Only a minority of fresh human clinical isolates of S. aureus elaborate PNSG in vitro but most could be induced to do so under specific in vitro growth conditions. However, by immunofluorescence microscopy, S. aureus cells in infected human sputa and lung elaborated PNSG. The ica genes, previously shown to encode proteins in CoNS that synthesize PNSG, were found by PCR in all S. aureus strains examined, and immunogenic and protective PNSG could be isolated from S. aureus. Active and passive immunization of mice with PNSG protected them against metastatic kidney infections after intravenous inoculation with eight phenotypically PNSG-negative S. aureus. Isolates recovered from kidneys expressed PNSG, but expression was lost with in vitro culture. Strong antibody responses to PNSG were elicited in S. aureus infected mice, and a PNSG-capsule was observed by electron microscopy on isolates directly plated from infected kidneys. PNSG represents a previously unidentified surface polysaccharide of S. aureus that is elaborated during human and animal infection and is a prominent target for protective antibodies.

Prophylactic and therapeutic efficacy of antibodies to a capsular polysaccharide shared among vancomycin-sensitive and -resistant enterococci

Enterococci are important nosocomial pathogens that are increasingly difficult to treat due to intrinsic and acquired resistance to antibiotics, including vancomycin. A recently described capsular polysaccharide (CP) isolated from Enterococcus faecalis 12030 was used to evaluate the potential efficacy of active or passive immunotherapy regimens as adjunctive treatments. Evaluation of protective efficacy was carried out in immunocompetent mice challenged intravenously (i.v.) with live enterococci. In nonimmune mice, i.v. inoculations resulted in high levels of bacteria in kidneys, spleens, and livers 5 days after challenge. Mice immunized with four 10-microg doses of CP antigen/mouse were protected against challenge with the homologous E. faecalis strain. High-titer opsonic immunoglobulin G was also induced by immunizing rabbits with the purified CP, and passive transfer of this antiserum to mice produced significantly lower bacterial counts in organs than did normal rabbit serum or sterile saline. Antibodies to the polysaccharide isolated from E. faecalis 12030 were protective against Enterococcus faecalis OG1RF and against two serologically related, vancomycin-resistant Enterococcus faecium clinical isolates. Antibodies to this CP antigen were also effective as a therapeutic reagent in mice when passive therapy was initiated 48 h after live bacterial challenge. These data indicate that CP antigens from enterococci are potential targets of protective antibodies and that these antibodies may be useful for prophylaxis and treatment of enterococcal infections.

Role of the cystic fibrosis transmembrane conductance regulator in innate immunity to Pseudomonas aeruginosa infections

Chronic Pseudomonas aeruginosa infection occurs in 75-90% of patients with cystic fibrosis (CF). It is the foremost factor in pulmonary function decline and early mortality. A connection has been made between mutant or missing CF transmembrane conductance regulator (CFTR) in lung epithelial cell membranes and a failure in innate immunity leading to initiation of P. aeruginosa infection. Epithelial cells use CFTR as a receptor for internalization of P. aeruginosa via endocytosis and subsequent removal of bacteria from the airway. In the absence of functional CFTR, this interaction does not occur, allowing for increased bacterial loads in the lungs. Binding occurs between the outer core of the bacterial lipopolysaccharide and amino acids 108-117 in the first predicted extracellular domain of CFTR. In experimentally infected mice, inhibiting CFTR-mediated endocytosis of P. aeruginosa by inclusion in the bacterial inoculum of either free bacterial lipopolysaccharide or CFTR peptide 108-117 resulted in increased bacterial counts in the lungs. CFTR is also a receptor on gastrointestinal epithelial cells for Salmonella enterica serovar Typhi, the etiologic agent of typhoid fever. There was a significant decrease in translocation of this organism to the gastrointestinal submucosa in transgenic mice that are heterozygous carriers of a mutant DeltaF508 CFTR allele, suggesting heterozygous CFTR carriers may have increased resistance to typhoid fever. The identification of CFTR as a receptor for bacterial pathogens could underlie the biology of CF lung disease and be the basis for the heterozygote advantage for carriers of mutant alleles of CFTR.

Establishment of Pseudomonas aeruginosa infection: lessons from a versatile opportunist

Pseudomonas aeruginosa is an ubiquitous pathogen capable of infecting virtually all tissues. A large variety of virulence factors contribute to its importance in burn wounds, lung infection and eye infection. Prominent factors include pili, flagella, lipopolysaccharide, proteases, quorum sensing, exotoxin A and exoenzymes secreted by the type III secretion system.

Acquisition of expression of the Pseudomonas aeruginosa ExoU cytotoxin leads to increased bacterial virulence in a murine model of acute pneumonia and systemic spread

Pseudomonas aeruginosa is the nosocomial bacterial pathogen most commonly isolated from the respiratory tract. Animal models of this infection are extremely valuable for studies of virulence and immunity. We thus evaluated the utility of a simple model of acute pneumonia for analyzing P. aeruginosa virulence by characterizing the course of bacterial infection in BALB/c mice following application of bacteria to the nares of anesthetized animals. Bacterial aspiration into the lungs was rapid, and 67 to 100% of the inoculum could be recovered within minutes from the lungs, with 0.1 to 1% of the inoculum found intracellularly shortly after infection. At later time points up to 10% of the bacteria were intracellular, as revealed by gentamicin exclusion assays on single-cell suspensions of infected lungs. Expression of exoenzyme U (ExoU) by P. aeruginosa is associated with a cytotoxic effect on epithelial cells in vitro and virulence in animal models. Insertional mutations in the exoU gene confer a noncytotoxic phenotype on mutant strains and decrease virulence for animals. We used the model of acute pneumonia to determine whether introduction of the exoU gene into noncytotoxic strains of P. aeruginosa lacking this gene affected virulence. Seven phenotypically noncytotoxic P. aeruginosa strains were transformed with pUCP19exoUspcU which carries the exoU gene and its associated chaperone. Three of these strains became cytotoxic to cultured epithelial cells in vitro. These strains all secreted ExoU, as confirmed by detection of the ExoU protein with specific antisera. The 50% lethal dose of exoU-expressing strains was significantly lower for all three P. aeruginosa isolates carrying plasmid pUCP19exoUspcU than for the isogenic exoU-negative strains. mRNA specific for ExoU was readily detected in the lungs of animals infected with the transformed P. aeruginosa strains. Introduction of the exoU gene confers a cytotoxic phenotype on some, but not all, otherwise-noncytotoxic P. aeruginosa strains and, for recombinant strains that could express ExoU, there was markedly increased virulence in a murine model of acute pneumonia and systemic spread.

Syndecan-1 shedding is enhanced by LasA, a secreted virulence factor of Pseudomonas aeruginosa

Microbial pathogens frequently take advantage of host systems for their pathogenesis. Shedding of cell surface molecules as soluble extracellular domains (ectodomains) is one of the host responses activated during tissue injury. In this study, we examined whether pathogenic bacteria can modulate shedding of syndecan-1, the predominant syndecan of host epithelia. Our studies found that overnight culture supernatants of Pseudomonas aeruginosa and Staphylococcus aureus enhanced the shedding of syndecan-1 ectodomains, whereas culture supernatants of several other Gram-negative and Gram-positive bacteria had only low levels of activity. Because supernatants from all tested strains of P. aeruginosa (n = 9) enhanced syndecan-1 shedding by more than 4-fold above control levels, we focused our attention on this Gram-negative bacterium. Culture supernatants of P. aeruginosa increased shedding of syndecan-1 in both a concentration- and time-dependent manner, and augmented shedding by various host cells. A 20-kDa shedding enhancer was partially purified from the supernatant through ammonium sulfate precipitation and gel chromatography, and identified by N-terminal sequencing as LasA, a known P. aeruginosa virulence factor. LasA was subsequently determined to be a syndecan-1 shedding enhancer from the findings that (i) immunodepletion of LasA from the partially purified sample resulted in abrogation of its activity to enhance shedding and (ii) purified LasA increased shedding in a concentration-dependent manner. Our results also indicated that LasA enhances syndecan-1 shedding by activation of the host cell's shedding mechanism and not by direct interaction with syndecan-1 ectodomains. Enhanced syndecan-1 shedding may be a means by which pathogenic bacteria take advantage of a host mechanism to promote their pathogenesis.

Impact of heterogeneity within cultured cells on bacterial invasion: analysis of Pseudomonas aeruginosa and Salmonella enterica serovar typhi entry into MDCK cells by using a green fluorescent protein-labelled cystic fibrosis transmembrane conductance regulator receptor

The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride ion channel that also serves as a receptor for entry of Pseudomonas aeruginosa and Salmonella enterica serovar Typhi into epithelial cells. To evaluate heterogeneity in CFTR protein expression in cultured cells and the effect of heterogeneity on internalization of different P. aeruginosa and serovar Typhi strains, we used two-color flow cytometry and confocal laser microscopy to study bacterial uptake by Madin-Darby canine kidney (MDCK) type I epithelial cells stably expressing a green fluorescent protein (GFP)-CFTR fusion construct (MDCK-GFP-CFTR cells). We found a strong correlation between cell size and GFP-CFTR protein expression, with 60 to 70% of cells expressing low levels of GFP-CFTR protein, 20 to 30% expressing intermediate levels, and <10% expressing high levels. The cells were sorted into low-, intermediate-, or high-level producers of CFTR protein; in vitro growth of each sorted population yielded the same distribution of CFTR protein expression as that in the original population. Cells expressing either low or high levels of CFTR protein internalized bacteria poorly; maximal bacterial uptake occurred in the cells expressing intermediate levels of CFTR protein. Treatment of MDCK cells with sodium butyrate markedly enhanced the production of CFTR protein without increasing cell size; butyrate treatment also increased the proportion of cells with internalized bacteria. However, there were fewer bacteria per butyrate-treated cell and, for P. aeruginosa, there was an overall decrease in the total level of bacterial uptake. The most highly ingested bacterial strains were internalized by fewer total MDCK-GFP-CFTR cells, indicating preferential bacterial uptake by a minority of epithelial cells within a given culture. Confocal fluorescence microscopy showed that P. aeruginosa and serovar Typhi induced cytoplasmic accumulation of CFTR protein close to the plasma membrane where the bacteria were adherent. These results show that within a population of MDCK-GFP-CFTR cells, there are cells with markedly different abilities to ingest bacteria via CFTR, the majority of the P. aeruginosa and serovar Typhi cells are ingested by the one-fourth to one-third of the cells that exhibit an intermediate size and level of CFTR protein expression, and overexpression of the CFTR receptor does not increase total bacterial uptake but rather allows more epithelial cells to ingest fewer total bacteria.

Pulmonary outcome in cystic fibrosis is influenced primarily by mucoid Pseudomonas aeruginosa infection and immune status and only modestly by genotype

Whether allelic variants of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) independently contribute to pulmonary outcome in CF patients has not been resolved. We used both cross-sectional and mixed-model longitudinal analyses of data from CF patients that were at least 12 years old to determine the influence on pulmonary function (percent predicted forced expiratory volume [FEV(1)]) of the CFTR gene genotype, gender, mucoid Pseudomonas aeruginosa (MPA) infection status, presence of total opsonic antibody to MPA, and, separately, the opsonic antibody activity specific to the mucoid exopolysaccharide (MEP) surface antigen. Two different factors were independently associated with the lack of MPA infection: a high level of MEP-specific opsonic activity (MSOA), implicating an immunologically based mechanism of resistance to infection, and a lack of any type of opsonic antibody to MPA, indicative of no significant exposure or infection. This latter phenotype was found in a subset of CF patients who carried at least one uncommon CFTR gene allele suggestive of a genetic basis for resistance to infection in this group of older CF patients. For CF patients in whom both CFTR gene alleles were identified by screening for the 12 most common variants (75% of alleles), cross-sectional analysis showed that MPA infection was best correlated with lower percent predicted FEV(1), while genotype (two versus one DeltaF508 CFTR gene allele) and a low level of MSOA were associated with increased risk of infection. A mixed-model analysis of longitudinal spirometric measurements that considered multiple risk factors to derive regression equations was used to determine which clinical parameters had the greatest effect on the annual rate of decline in percent predicted FEV(1). This analysis showed that the CFTR gene genotype only modestly modified the constant (y intercept) of the derived equations, while gender and MPA infection status had the largest effects on annual rates of decline in percent predicted FEV(1). These results indicate that the CFTR genotype is usually not a primary determinant of pulmonary function in most CF patients, but gender and MPA infection status are. Infection status is potentially influenced by both immunologic (a high level of MSOA) and genetic factors, such as carriage of a CFTR gene allele that leads to a diagnosis of CF but still confers resistance to infection that is comparable to that of the wild-type CFTR gene.

Characterization of the serogroup O11 O-antigen locus of Pseudomonas aeruginosa PA103

We previously cloned a genomic DNA fragment from the serogroup O11 Pseudomonas aeruginosa strain PA103 that contained all genes necessary for O-antigen synthesis and directed the expression of serogroup O11 antigen on recombinant Escherichia coli and Salmonella. To elucidate the pathway of serogroup O11 antigen synthesis, the nucleotide sequence of the biosynthetic genes was determined. Eleven open reading frames likely to be involved in serogroup O11 O-antigen biosynthesis were identified and are designated in order as wzzPaO111 (wzz from P. aeruginosa serogroup O11), wzxPaO11, wbjA, wzyPaO11, wbjB to wbjF, wbpLO11 and wbpMO11 (wbpL and wbpM from serogroup O11). Consistent with previous descriptions of O-antigen biosynthetic gene loci, the entire region with the exception of wbpMO11 has a markedly reduced G+C content relative to the chromosomal average. WzyPaO11 shows no significant similarity at the protein or DNA sequence level to any database sequence and is very hydrophobic, with 10 to 12 putative transmembrane domains, both typical characteristics of O-antigen polymerases. A nonpolar chromosomal insertion mutation in wzyPaO11 in P. aeruginosa PA103 confirmed the identity of this gene. There is striking similarity between WbjBCDE and Cap(5/8)EFGL, involved in type 5 and type 8 capsule biosynthesis in Staphylococcus aureus. There is nearly total identity between wbpMO11 and wbpMO5, previously shown by others to be present in all 20 P. aeruginosa serogroups. Using similarity searches, we have assigned functions to the proteins encoded by the PA103 O-antigen locus and present the potential steps in the pathway for the biosynthesis of P. aeruginosa serogroup O11 O antigen.

Broadly protective vaccine for Staphylococcus aureus based on an in vivo-expressed antigen

Vaccines based on preferential expression of bacterial antigens during human infection have not been described. Staphylococcus aureus synthesized poly-N-succinyl beta-1-6 glucosamine (PNSG) as a surface polysaccharide during human and animal infection, but few strains expressed PNSG in vitro. All S. aureus strains examined carried genes for PNSG synthesis. Immunization protected mice against kidney infections and death from strains that produced little PNSG in vitro. Nonimmune infected animals made antibody to PNSG, but serial in vitro cultures of kidney isolates yielded mostly cells that did not produce PNSG. PNSG is a candidate for use in a vaccine to protect against S. aureus infection.

Structure of an antigenic teichoic acid shared by clinical isolates of Enterococcus faecalis and vancomycin-resistant Enterococcus faecium

A shared antigenic teichoic acid, previously found to be a surface capsule-like polysaccharide, was isolated from clinical isolates of Enterococcus faecalis and vancomycin-resistant E. faecium. It was composed of glucose, glycerol, and phosphate as determined by chemical and GC-MS analysis. The repeating-unit structure was elucidated by a series of 1H, 13C, and 31P NMR spectroscopy to be the following: [formula: see text]

Isolation and chemical characterization of a capsular polysaccharide antigen shared by clinical isolates of Enterococcus faecalis and vancomycin-resistant Enterococcus faecium

Enterococci are a common cause of serious infections, especially in newborns, severely immunocompromised patients, and patients requiring intensive care. To characterize enterococcal surface antigens that are targets of opsonic antibodies, rabbits were immunized with various gentamicin-killed Enterococcus faecalis strains, and immune sera were tested in an opsonophagocytic assay against a selection of clinical isolates. Serum raised against one strain killed the homologous strain (12030) at a dilution of 1:5,120 and mediated opsonic killing of 33% of all strains tested. In addition, this serum killed two (28%) of seven vancomycin-resistant Enterococcus faecium strains. Adsorption of sera with the homologous strain eliminated killing activity. The adsorbing antigens were resistant to treatment with proteinase K and to boiling for 1 h, but were susceptible to treatment with sodium periodate, indicating that the antigen inducing opsonic activity is a polysaccharide. Antibodies in immune rabbit sera reacted with a capsule-like structure visualized by electron microscopy both on the homologous E. faecalis strain and on a vancomycin-resistant E. faecium strain. The capsular polysaccharides from E. faecalis 12030 and E. faecium 838970 were purified, and chemical and structural analyses indicated they were identical glycerol teichoic acid-like molecules with a carbohydrate backbone structure of 6-alpha-D-glucose-1-2 glycerol-3-PO4 with substitution on carbon 2 of the glucose with an alpha-2-1-D-glucose residue. The purified antigen adsorbed opsonic killing activity from immune rabbit sera and elicited high titers of antibodies (when used to immunize rabbits) that both mediated opsonic killing of bacteria and bound to a capsule-like structure visualized by electron microscopy. These results indicate that approximately one-third of a sample of 15 E. faecalis strains and 7 vancomycin-resistant E. faecium strains possess shared capsular polysaccharides that are targets of opsonophagocytic antibodies and therefore are potential vaccine candidates.

Cystic fibrosis transmembrane conductance regulator-mediated corneal epithelial cell ingestion of Pseudomonas aeruginosa is a key component in the pathogenesis of experimental murine keratitis

Previous findings indicate that the cystic fibrosis transmembrane conductance regulator (CFTR) is a ligand for Pseudomonas aeruginosa ingestion into respiratory epithelial cells. In experimental murine keratitis, P. aeruginosa enters corneal epithelial cells. We determined the importance of CFTR-mediated uptake of P. aeruginosa by corneal cells in experimental eye infections. Entry of noncytotoxic (exoU) P. aeruginosa into human and rabbit corneal cell cultures was inhibited with monoclonal antibodies and peptides specific to CFTR amino acids 108 to 117. Immunofluorescence microscopy and flow cytometry demonstrated CFTR in the intact murine corneal epithelium, and electron microscopy showed that CFTR binds to P. aeruginosa following corneal cell ingestion. In experimental murine eye infections, multiple additions of 5 nM CFTR peptide 103-117 to inocula of either cytotoxic (exoU+) or noncytotoxic P. aeruginosa resulted in large reductions in bacteria in the eye and markedly lessened eye pathology. Compared with wild-type C57BL/6 mice, heterozygous DeltaF508 Cftr mice infected with P. aeruginosa had an approximately 10-fold reduction in bacterial levels in the eye and consequent reductions in eye pathology. Homozygous DeltaF508 Cftr mice were nearly completely resistant to P. aeruginosa corneal infection. CFTR-mediated internalization of P. aeruginosa by buried corneal epithelial cells is critical to the pathogenesis of experimental eye infection, while in the lung, P. aeruginosa uptake by surface epithelial cells enhances P. aeruginosa clearance from this tissue.

The ica locus of Staphylococcus epidermidis encodes production of the capsular polysaccharide/adhesin

Clinical isolates of coagulase-negative staphylococci often elaborate a biofilm involved in adherence to medical devices and resistance to host defenses. The biofilm contains the capsular polysaccharide/adhesin (PS/A), which mediates cell adherence to biomaterials, and another antigen, termed polysaccharide intercellular adhesin (PIA), which is thought to mediate bacterial accumulation into cellular aggregates. PIA is a polymer of beta-1, 6-linked N-acetyl glucosamine residues with a molecular mass of <30, 000 kDa. We found that recombinant Staphylococcus carnosus and Staphylococcus aureus carrying a plasmid with genes of the ica locus, which was reported to encode the biosynthetic proteins for production of PIA, were also able to synthesize PS/A. PS/A and a chemically and immunologically identical polysaccharide isolated from S. carnosus carrying the ica genes on plasmid pCN27 were found to be high-molecular-mass (>250,000 kDa), acid-stable polymers of beta-1,6-linked glucosamine substituted on the amino group primarily with succinate, although some preparations also contained acetate. Moreover, all recombinant staphylococcal strains with the ica genes had the biologic properties previously attributed to PS/A. ica-positive strains readily formed an in vitro biofilm on plastic, adhered 3- to 10-fold more to catheters during a 30-min assay compared with control strains carrying only the cloning vector, adsorbed out antibodies to PS/A from immune serum, and elaborated a capsule visualized by immunoelectron microscopy with antisera to PS/A. These properties were also seen with PS/A-producing strains of Staphylococcus epidermidis, but not with transposon mutants lacking PS/A. An antiserum raised to PIA contained high-titer antibody to PS/A that was readily adsorbed out by PS/A-positive strains of S. epidermidis and recombinant strains of staphylococci carrying the ica genes. We conclude that the ica locus encodes production of PS/A and that the properties of S. epidermidis associated with initial bacterial adherence, biofilm formation, and intercellular adhesion can be correlated with elaboration of PS/A.

Production and characterization of a set of mouse-human chimeric immunoglobulin G (IgG) subclass and IgA monoclonal antibodies with identical variable regions specific for Pseudomonas aeruginosa serogroup O6 lipopolysaccharide

The heavy- and light-chain variable regions from a murine monoclonal antibody that recognize Pseudomonas aeruginosa serogroup O6 lipopolysaccharide (LPS) were used to generate a series of chimeric mouse-human monoclonal antibodies with identical variable regions. The murine variable-region gene segments were cloned into an immunoglobulin (Ig) cDNA expression vector that contained the human kappa light-chain and IgG1 constant regions. The IgG1 heavy-chain constant region was then replaced with the human IgG2, IgG3, IgG4, or IgA1 heavy-chain constant region. The five different expression vectors were transfected into Chinese hamster ovary cells for antibody production. The chimeric antibodies exhibited immunoreactivity and affinity similar to that of the parental murine IgG antibody toward whole cells of a serogroup O6 strain. In vitro complement deposition assays demonstrated that the chimeric IgG4 and IgA antibodies did not mediate the deposition of complement component C3 onto the surface of either purified LPS or whole bacteria. The chimeric IgG1 and IgG3 antibodies were similar in their ability to deposit C3 onto the surface of both bacteria and LPS, while IgG2 antibody was more effective at depositing C3 onto the surface of bacteria than onto purified LPS. The pattern of opsonophagocytic activity of the chimeric monoclonal antibodies was similar to that of complement deposition onto bacterial cells in that the chimeric IgG1 and IgG3 had the highest opsonic activity. Although IgG2 deposited more C3 onto the bacterial surface than did IgG4 or IgA, all three of these isotypes had low opsonic activity against the serogroup O6 target strain. This series of related antibodies will help reveal functional differences in efficacy among protective antibodies to P. aeruginosa and will be critical for defining the optimal formulation of either a vaccine for active immunization or a polyclonal intravenous IgG or monoclonal antibody cocktail for passive immunotherapy.

Complex serology and immune response of mice to variant high-molecular-weight O polysaccharides isolated from Pseudomonas aeruginosa serogroup O2 strains

The O antigen of the Pseudomonas aeruginosa lipopolysaccharide is the optimal target for protective antibodies, but the unusual and complex nature of their sugar substituents has made it difficult to define the range of these structures needed in an effective vaccine. Most clinical isolates of P. aeruginosa can be classified into 10 O-antigen serogroups, but slight chemical differences among O polysaccharides within a serogroup give rise to subtype epitopes. These epitopes could impact the reactivity of O-antigen-specific antibodies, as well as the susceptibility of a target strain to protective, opsonic antibodies. To define parameters of serogroup and subtype-epitope immunogenicity, antigenicity, and surface expression on P. aeruginosa cells, we prepared high-molecular-weight O-polysaccharide vaccines from strains of P. aeruginosa serogroup O2, for which eight structurally variant O antigens expressing six defined subtype epitopes (O2a to O2f) have been identified. A complex pattern of immune responses to these antigens was observed following vaccination of mice. The high-molecular-weight O polysaccharides were generally more immunogenic at low doses (1 and 10 microg) than at a high dose (50 microg) and usually elicited antibodies that opsonized the homologous strain for phagocytic killing. Some of the individual polysaccharides elicited cross-opsonic antibodies to a variable number of strains that express all of the defined serogroup O2 subtype epitopes. Combination into one vaccine of two antigens that individually elicited cross-reactive opsonic antibodies to most members of the O2 serogroup inhibited, instead of enhanced, the production of antibodies broadly reactive with most serogroup O2 subtype strains. Thus, immune responses to P. aeruginosa O antigens may be restricted to a limited range of epitopes on structurally complex O antigens, and combining multiple related antigens into a single vaccine formulation may inhibit the production of those antibodies best able to protect against most P. aeruginosa strains within a given O-antigen serogroup.

Salmonella typhi uses CFTR to enter intestinal epithelial cells

Homozygous mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis (CF). In the heterozygous state, increased resistance to infectious diseases may maintain mutant CFTR alleles at high levels in selected populations. Here we investigate whether typhoid fever could be one such disease. The disease is initiated when Salmonella typhi enters gastrointestinal epithelial cells for submucosal translocation. We found that S. typhi, but not the related murine pathogen S. typhimurium, uses CFTR for entry into epithelial cells. Cells expressing wild-type CFTR internalized more S. typhi than isogenic cells expressing the most common CFTR mutation, a phenylalanine deleted at residue 508 (delta508). Monoclonal antibodies and synthetic peptides containing a sequence corresponding to the first predicted extracellular domain of CFTR inhibited uptake of S. typhi. Heterozygous deltaF508 Cftr mice translocated 86% fewer S. typhi into the gastrointestinal submucosa than wild-type Cftr mice; no translocation occurred in deltaF508 Cftr homozygous mice. The Cftr genotype had no effect on the translocation of S. typhimurium. Immunoelectron microscopy revealed that more CFTR bound to S. typhi in the submucosa of Cftr wild-type mice than in deltaF508 heterozygous mice. We conclude that diminished levels of CFTR in heterozygotes may decrease susceptibility to typhoid fever.

Cystic fibrosis transmembrane conductance regulator is an epithelial cell receptor for clearance of Pseudomonas aeruginosa from the lung

The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride ion channel, but its relationship to the primary clinical manifestation of CF, chronic Pseudomonas aeruginosa pulmonary infection, is unclear. We report that CFTR is a cellular receptor for binding, endocytosing, and clearing P. aeruginosa from the normal lung. Murine cells expressing recombinant human wild-type CFTR ingested 30-100 times as many P. aeruginosa as cells lacking CFTR or expressing mutant DeltaF508 CFTR protein. Purified CFTR inhibited ingestion of P. aeruginosa by human airway epithelial cells. The first extracellular domain of CFTR specifically bound to P. aeruginosa and a synthetic peptide of this region inhibited P. aeruginosa internalization in vivo, leading to increased bacterial lung burdens. CFTR clears P. aeruginosa from the lung, indicating a direct connection between mutations in CFTR and the clinical consequences of CF.

Contribution of proteases and LasR to the virulence of Pseudomonas aeruginosa during corneal infections

The roles of the Pseudomonas aeruginosa proteases LasB (elastase) and LasA and the transcriptional activator LasR, which regulates the expression of these proteases, were evaluated in a murine model of P. aeruginosa corneal infection. In scarified corneas, P. aeruginosa PAO-A1 (LasA negative) or PAO-B1A1 (LasB and LasA negative) at a dose of 10(8) CFU per eye caused very mild or no disease following infection; however, the defect in PAO-A1 could not be complemented by supplying a functional copy of lasA either on a plasmid or inserted into the chromosome. In contrast, PAO-B1 (LasB negative) colonized the cornea and caused disease equal in severity to disease caused by the parental strain, PAO1-I. Although LasR is a known regulator of lasA expression, PAO-R1, a lasR-negative derivative of PAO1-I, was as virulent as the parental strain during corneal infection. When transcriptional fusion plasmids were used to quantify the expression of the lasB and lasA genes in P. aeruginosa PAO1-I and PAO-R1, the lasB::lacZ fusion in PAO-R1 showed only 3.5% as much activity as it did in PAO1-I, while the activity of the lasA::lacZ fusion in PAO-R1 was 27.8% of that in PAO1-I. Coadministration of 5 microg of purified LasA protease with PAO-A1 did not reconstitute a wild-type infection. This treatment produced an acute toxic reaction leading to prolonged eyelid closure without inflammatory destruction of the cornea that was similar to that observed when LasA was administered alone. These results indicate that insertional inactivation of lasA renders P. aeruginosa avirulent in a murine model of keratitis and that neither LasR nor elastase production is required for the establishment and maintenance of corneal infection. However, the lack of virulence of the LasA-deficient strains cannot be ascribed with certainty to the deficiency of LasA from the available data.

Prophylactic and therapeutic efficacy of immunoglobulin G antibodies to Pseudomonas aeruginosa lipopolysaccharide against murine experimental corneal infection

PURPOSE

To evaluate the efficacy of lipopolysaccharide (LPS)-specific antibodies administered prophylactically or therapeutically to protect against corneal challenge with Pseudomonas aeruginosa.

METHODS

The prophylactic efficacy of active immunization with purified P. aeruginosa LPS was evaluated in a murine corneal-scratch model of P. aeruginosa keratitis. The same model was used to evaluate both the prophylactic and the therapeutic efficacy of systemic passive transfer of variable region-identical, isotype-switched, LPS-specific, murine immunoglobulin M (IgM) and immunoglobulin G (IgG) monoclonal antibodies (mAbs). The mAbs were injected intraperitoneally at various times either before or after corneal challenge and the corneal response was monitored macroscopically. In addition, immune rabbit sera were used to evaluate the efficacy of treatment.

RESULTS

Active immunization with homologous, but not heterologous, LPS before challenge reduced the severity of corneal disease and protected challenged mice against permanent corneal damage. Passive transfer of the LPS-specific IgM mAb 1F6 before challenge did not prevent corneal damage at any dose tested and had no effect on the course of disease. However, results of dose-response studies of the passive transfer of a variable region-identical IgG2b mAb, 2H3, before challenge indicated a 50% protective dose of 11.8 micrograms. When mAb 2H3 was administered at a dose of 50 micrograms before challenge and the challenge inoculum was increased, all mice were protected from corneal damage up to a challenge inoculum of 2.2 x 10(8) CFU/eye. When given 2 or 4 hours after corneal challenge with P. aeruginosa strain 6294 (which invades corneal epithelial cells during infection) but not when given at 8 or 24 hours, 50 micrograms of mAb 2H3 conferred significant protection (P < 0.05). The maximal interval after challenge during which this antibody could be administered and still protect 50% of mice was calculated by probit analysis to be 9.4 hours. Administration of homologous LPS-specific rabbit antiserum to mice at various times after challenge with P. aeruginosa strain 6206 (which is cytotoxic to corneal epithelial cells and does not remain in these cells during infection) resulted in significant protection when administered 4 or 8 hours after infection. Although probit analysis could not be performed with the available data, 50% of mice were completely protected when the antiserum was given up to 24 hours after challenge.

CONCLUSIONS

In an experimental model of P. aeruginosa keratitis, systematically delivered IgG antibodies directed against the O-side-chain antigens of P. aeruginosa, LPS conferred protection against severe corneal damage when administered both prophylactically and therapeutically.

Inhibition of bacterial adherence to host tissue does not markedly affect disease in the murine model of Pseudomonas aeruginosa corneal infection

The prevention of bacterial infections by the inhibition of binding to host tissues is an oft-touted approach, but few studies with appropriate models of infection have tested its feasibility. Pseudomonas aeruginosa causes severe corneal infections in mice after inoculations with low doses, and infection is thought to depend upon an initial adherence of the bacteria to corneal cells. In vitro, adherence to corneal cells is mediated to a large degree by the complete-outer-core oligosaccharide of the bacterial lipopolysaccharide (LPS). However, bacteria adhering to tissues in vivo are difficult to differentiate from nonadherent bacteria. Since a direct correlate of P. aeruginosa adherence to corneal epithelial cells is the degree to which these cells internalize P. aeruginosa, the level of adherence in vivo can be approximated by measuring P. aeruginosa ingestion by cells by using gentamicin exclusion assays. To determine the degree to which inhibition of the corneal cell adherence affects the course of infection and disease in the murine model, we evaluated the ability of LPS-outer-core oligosaccharide to inhibit bacterial association and entry into corneal cells and to modulate the development of disease. Mice were anesthetized, and their corneas were scratched and inoculated with virulent P. aeruginosa 6294 or PAO1, along with either 50 microg of oligosaccharide derived from LPS from P. aeruginosa PAC557 (complete outer core but no O side chains) or oligosaccharide derived from LPS of P. aeruginosa PAC1RalgC::tet (incomplete-core oligosaccharide). After 4 h, there were no differences between groups in the counts of infecting and internalized bacteria. At 24 h, the complete-core oligosaccharide decreased the levels of bacteria per eye by 70 to 99.7% compared with the levels achieved by including the incomplete-core oligosaccharide in the infectious inoculum. Epithelial cell ingestion of bacteria was comparably affected. However, the effect on disease was modest and only evident at lower challenge doses that elicited mild disease in controls and when the bacterial association and ingestion were inhibited by >99%. Overall, it appears that in the murine model of P. aeruginosa corneal infection at challenge doses of bacteria 10-fold or greater than the minimal amount needed to cause disease, the absolute level of inhibition of bacterial adherence is insufficient to reduce the bacterial counts below that which elicits disease.

Rationale for development of immunotherapies that target mucoid Pseudomonas aeruginosa infection in cystic fibrosis patients

Despite a complex sputum bacteriology, the progressive decline in pulmonary function that is the hallmark of the genetic disease cystic fibrosis (CF) is attributable to a single infecting pathogen, mucoid Pseudomonas aeruginosa. Therefore, active and passive immunotherapies that target this particular variant of the bacterium should be of value in attenuating infection and interfering with the decline in pulmonary function. The major surface antigen of mucoid P. aeruginosa is referred to as either mucoid exopolysaccharide (MEP) or alginate, a random polymer of D-mannuronic and L-guluronic acid residues linked beta 1-4. During chronic infection CF patients make antibodies to MEP that fail to mediate opsonic killing of bacteria in vitro. These antibodies can be elicited by vaccination in 35-40% of plasma donors given a preparation of MEP comprised of only the highest molecular-weight polymers; inclusion in human vaccines of smaller polymers normally produced by the bacterium fails to elicit opsonic antibodies, just like in infected CF patients. Opsonic, but not non-opsonic, antibodies to MEP protect animals against chronic endobronchial infection. CF patients do produce opsonic antibodies to mucoid P. aeruginosa that are in a planktonic or suspended state, but these antibodies are not directed at the MEP antigen and they fail to kill P. aeruginosa growing in a biofilm. This is the state that the bacteria grow in the lung. Therefore immunoglobulin G preparations with opsonic antibodies to MEP could provide CF patients with antibodies that they normally do not produce during chronic lung infection and may improve their clinical course.

How mutant CFTR may contribute to Pseudomonas aeruginosa infection in cystic fibrosis

Patients with cystic fibrosis (CF) have a pronounced hypersusceptibility (80 to 90%) to Pseudomonas aeruginosa infection. We hypothesized that airway epithelial cell ingestion of bacteria followed by cellular desquamation may protect the lung from infection, and epithelial cells expressing mutant forms of the cystic fibrosis transmembrane conductance regulator (CFTR) may be defective in this function. We found that transformed human airway epithelial cells homozygous for the delta F508 allele of CFTR were significantly defective in uptake of P. aeruginosa compared with the same cell line complemented with the wild-type allele of CFTR. Partial membrane expression of the delta F508 CFTR protein occurs in cells grown at 26 degrees C, and under these conditions uptake of P. aeruginosa occurred at levels comparable to cells with a wild-type allele of CFTR. Epithelial cell ingestion assays using isogenic bacterial strains differing in lipopolysaccharide (LPS) phenotype, along with inhibition studies, identified the LPS-core oligosaccharide as the bacterial ligand for epithelial cell invasion. Inhibition of epithelial cell ingestion of P. aeruginosa in a neonatal mouse lung infection model led to increased levels of bacteria in the lungs 24 and 48 h after infection. Defective epithelial cell internalization of P. aeruginosa may be a critical factor in hypersusceptibility of CF patients to chronic lung infections.

Factors affecting Staphylococcus epidermidis adhesion to contact lenses

BACKGROUND

Staphylococcus epidermidis is a major causative agent of infectious keratitis associated with contact lens wear. Adhesion of this bacterium to contact lenses may contribute to the pathogenesis of infection and could be influenced by lens surface properties, packaging/storage solutions, and vary among different strains according to the level or type of adhesins expressed.

METHODS

Adhesion of six clinical isolates of S. epidermidis to three different contact lens materials was tested. Adhesion assays were performed on lenses immediately after removal from their packages, and also after lenses were soaked in sterile phosphate buffered saline (PBS) for 7 days to dilute the packaging solution.

RESULTS

For lenses tested immediately upon removal from their packaging, adhesion to polymacon (in PBS with 0.1% polyvinyl alcohol) was significantly greater than to etafilcon A (in borate buffered saline) and vifilcon A (in PBS). After soaking, adhesion to polymacon lenses was significantly less than to the other lens materials. This pattern was consistent for all strains, although major differences in baseline adhesion levels existed between strains, with exopolysaccharide (slime)-positive bacteria being more adherent to lenses.

CONCLUSIONS

Properties of contact lens materials were not the sole determinant of viable S. epidermidis adhesion to lenses. Strain variability, including levels of exopolysaccharide expression, and the solution used for lens immersion also influenced adhesion.

Relationship between cytotoxicity and corneal epithelial cell invasion by clinical isolates of Pseudomonas aeruginosa

We have reported that some strains of Pseudomonas aeruginosa can enter corneal epithelial cells during experimental murine eye infection and when the cells are cultured in vitro. Following invasion, both the host cell and the intracellular bacteria can remain viable for up to 24 h. Others have reported that toxin-mediated damage of epithelial cells contributes to the pathogenesis of P. aeruginosa keratitis. To clarify the relationship between cell invasion and cytotoxicity, fourteen P. aeruginosa isolates were compared for their capacity to enter epithelial cells and for their ability to induce cytotoxicity. Bacterial invasion was quantified by gentamicin survival assays both in vivo and in vitro. Cytotoxicity was examined qualitatively by trypan blue exclusion assays and quantitatively by chromium release assays in vitro. A significant inverse correlation was found between the ability to induce cytotoxicity and epithelial cell invasion as measured by gentamicin survival assays. Both cytotoxic and noncytotoxic strains were identified among corneal and noncorneal isolates; all isolates that were not cytotoxic were capable of epithelial cell invasion. Efficient host cell invasion could not be demonstrated for cytotoxic strains; however, the gentamicin survival assay relies upon host cells retaining viability in order to yield useful results, and this may limit the effectiveness of this assay for testing epithelial cell invasion by cytotoxic strains. Since all of the corneal isolates that were tested were virulent in vivo, the results show that there are at least two different types of P. aeruginosa-induced disease, one caused by strains that are cytotoxic and the other involving bacteria that can enter epithelial cells and survive intracellularly without killing the host cell.

Lipopolysaccharide outer core is a ligand for corneal cell binding and ingestion of Pseudomonas aeruginosa

PURPOSE

Pseudomonas aeruginosa has been observed to be adherent to and inside epithelial cells during experimental corneal infection. The authors identified bacterial ligands involved in adherence and entry of P. aeruginosa into corneal epithelial cells.

METHODS

In vitro gentamicin survival assays were used to determine the intracellular survival of a panel of P. aeruginosa mutants. Strains (10(6) to 10(7) colony-forming units) were added to primary cultures of rabbit corneal epithelial cells (approximately 10(5)/well) for 3 hours, nonadherent bacteria were washed away, and extracellular bacteria were killed with gentamicin. The antibiotic was then washed away, and epithelial cells were lysed with 0.5% Triton X-100 to release internalized bacteria. Bacterial association (sum of bound and internalized bacteria) was measured by the omission of gentamicin. Similar assays were carried out with whole mouse eyes in situ.

RESULTS

A lipopolysaccharide core with an exposed terminal glucose residue was found to be necessary for maximal association and entry of P. aeruginosa into corneal cells. Bacterial pili and flagella were not involved. Mutants of P. aeruginosa strains that do not produce an LPS core with a terminal glucose residue had a significantly lower level of association with (approximately 50%) and ingestion by ( > 90%, P < 0.01) corneal cells than did strains with this characteristic. Complementation of the LPS productions defect by plasmid-borne DNA returned association and ingestion to near parental levels. Lipopolysaccharides and delipidated oligosaccharides with a terminal glucose residue in the core inhibited bacterial association and entry into corneal cells. Experiments using P. aeruginosa LPS mutants and corneal cells on whole mouse eyes confirmed the role of the LPS core in cellular entry.

CONCLUSIONS

Corneal epithelial cells bind and internalized P. aeruginosa by the exposed LPS core.

Role of mutant CFTR in hypersusceptibility of cystic fibrosis patients to lung infections

Cystic fibrosis (CF) patients are hypersusceptible to chronic Pseudomonas aeruginosa lung infections. Cultured human airway epithelial cells expressing the delta F508 allele of the cystic fibrosis transmembrane conductance regulator (CFTR) were defective in uptake of P. aeruginosa compared with cells expressing the wild-type allele. Pseudomonas aeruginosa lipopolysaccharide (LPS)-core oligosaccharide was identified as the bacterial ligand for epithelial cell ingestion; exogenous oligosaccharide inhibited bacterial ingestion in a neonatal mouse model, resulting in increased amounts of bacteria in the lungs. CFTR may contribute to a host-defense mechanism that is important for clearance of P. aeruginosa from the respiratory tract.

The pathogenic role of Staphylococcus epidermidis capsular polysaccharide/adhesin in a low-inoculum rabbit model of prosthetic valve endocarditis

BACKGROUND

The capsular polysaccharide/adhesin (PS/A) antigen of Staphylococcus epidermidis was required to produce endocarditis in a rabbit model in which infection resulted from hematogenous spread of bacteria from a contaminated catheter in the jugular vein. However, many prosthetic valve endocarditis (PVE) infections probably result from direct contamination of the valve with small numbers of bacteria during surgery. The role of PS/A in this situation was evaluated by modifying a rabbit model of endocarditis to partially mimic PVE.

METHODS AND RESULTS

A Teflon catheter was contaminated with graded inocula of either PS/A-positive S epidermidis strain M187sp11 or the PS/A-negative, isogenic strain M187sn3 and inserted into the left ventricle through the aortic valve. The PS/A-positive strain had a 50% infectious dose of 1.1 x 10(2) cfu (95% CI, 3.3 to 3.7 x 10(3)) compared with 8.5 x 10(4) cfu of the PS/A-negative strain (95% CI, 8.6 x 10(3) to 8.5 x 10(5)). The odds for developing endocarditis were estimated to be 42 times higher for any given inoculum level of the PS/A-positive strain (P = .1). When the PS/A-positive strain was adherent to a catheter surface it survived in rabbit blood, whereas under the same conditions the PS/A-negative strain was killed approximately 90% in 1 hour.

CONCLUSIONS

Direct contamination of an intraventricular foreign body by low levels of PS/A-positive S epidermidis results in endocarditis in rabbits, but at suitably high doses PS/A-negative strains have sufficient virulence to infect cardiac vegetations. PS/A enhances but is not absolutely required for bacterial virulence in a rabbit model of PVE.