Role of anti-pilus antibodies in host defense against gonococcal infection studied with monoclonal anti-pilus antibodies

Meningococcal surface fibril (Msf) binds to activated vitronectin and inhibits the terminal complement pathway to increase serum resistance

Complement evasion is an important survival strategy of Neisseria meningitidis (Nm) during colonization and infection. Previously, we have shown that Nm Opc binds to serum vitronectin to inhibit complement-mediated killing. In this study, we demonstrate meningococcal interactions with vitronectin via a novel adhesin, Msf (meningococcal surface fibril, previously NhhA or Hsf). As with Opc, Msf binds preferentially to activated vitronectin (aVn), engaging at its N-terminal region but the C-terminal heparin binding domain may also participate. However, unlike Opc, the latter binding is not heparin-mediated. By binding to aVn, Msf or Opc can impart serum resistance, which is further increased in coexpressers, a phenomenon dependent on serum aVn concentrations. The survival fitness of aVn-binding derivatives was evident from mixed population studies, in which msf/opc mutants were preferentially depleted. In addition, using vitronectin peptides to block Msf-aVn interactions, aVn-induced inhibition of lytic C5b-9 formation and of serum killing could be reversed. As Msf-encoding gene is ubiquitous in the meningococcal strains examined and is expressed in vivo, serum resistance via Msf may be of significance to meningococcal pathogenesis. The data imply that vitronectin binding may be an important strategy for the in vivo survival of Nm for which the bacterium has evolved redundant mechanisms.

Testing the vaccine potential of PilV, PilX and ComP, minor subunits of Neisseria meningitidis type IV pili

Because meningitis and septicaemia caused by Neisseria meningitidis are major public health problems worldwide, the design of a broadly protective vaccine remains a priority. Type IV pili (Tfp) are surface-exposed filaments playing a key role in pathogenesis in a variety of bacterial species, including N. meningitidis, that have demonstrated vaccine potential. Unfortunately, in the meningococcus, the major pilus subunit PilE usually undergoes extensive antigenic variation and is therefore not suitable as a vaccine component. However, we have recently shown that N. meningitidis Tfp contain low abundance subunits PilX, PilV and ComP, collectively called minor pilins, that are highly conserved and modulate Tfp-linked functions key to pathogenesis. This prompted us to examine the vaccine potential of these proteins by assessing whether sera directed against them have bactericidal properties and/or are able to interfere with Tfp-linked functions. Here we show that minor pilin proteins are recognized by sera of patients convalescent from meningococcal disease and that antibodies directed against some of them can selectively interfere with Tfp-linked functions. This shows that, despite their apparent inability to elicit bactericidal antibodies, minor pilins might have vaccine potential.

New concepts in immunity to Neisseria gonorrhoeae: innate responses and suppression of adaptive immunity favor the pathogen, not the host

It is well-known that gonorrhea can be acquired repeatedly with no apparent development of protective immunity arising from previous episodes of infection. Symptomatic infection is characterized by a purulent exudate, but the host response mechanisms are poorly understood. While the remarkable antigenic variability displayed by Neisseria gonorrhoeae and its capacity to inhibit complement activation allow it to evade destruction by the host's immune defenses, we propose that it also has the capacity to avoid inducing specific immune responses. In a mouse model of vaginal gonococcal infection, N. gonorrhoeae elicits Th17-driven inflammatory–immune responses, which recruit innate defense mechanisms including an influx of neutrophils. Concomitantly, N. gonorrhoeae suppresses Th1- and Th2-dependent adaptive immunity, including specific antibody responses, through a mechanism involving TGF-β and regulatory T cells. Blockade of TGF-β alleviates the suppression of specific anti-gonococcal responses and allows Th1 and Th2 responses to emerge with the generation of immune memory and protective immunity. Genital tract tissues are naturally rich in TGF-β, which fosters an immunosuppressive environment that is important in reproduction. In exploiting this niche, N. gonorrhoeae exemplifies a well-adapted pathogen that proactively elicits from its host innate responses that it can survive and concomitantly suppresses adaptive immunity. Comprehension of these mechanisms of gonococcal pathogenesis should allow the development of novel approaches to therapy and facilitate the development of an effective vaccine.

Why do we need quality-assured diagnostic tests for sexually transmitted infections?

The bacterial sexually transmitted infections (STIs) syphilis, gonorrhoea and chlamydia can all be cured with a single dose of antibiotic. Unfortunately, however, these infections often remain undiagnosed as many infected individuals have few if any symptoms. Diagnostic tests with high sensitivity and specificity are available for all three infections but, owing to their expense and the lack of laboratory capacity, most people in developing countries do not have access to these tests. There is a great need for simple, cheap diagnostic tests for STIs that can be performed at the point of care, enabling treatment to be given immediately. It is hoped that recent advances in our understanding of the pathogenesis of these infections, and the availability of the complete genome sequences for each causative organism, will lead to the development of improved point-of-care tests that will reduce the burden of these diseases in developing countries.

Why do we need quality-assured diagnostic tests for sexually transmitted infections?

The bacterial sexually transmitted infections (STIs) syphilis, gonorrhoea and chlamydia can all be cured with a single dose of antibiotic. Unfortunately, however, these infections often remain undiagnosed as many infected individuals have few if any symptoms. Diagnostic tests with high sensitivity and specificity are available for all three infections but, owing to their expense and the lack of laboratory capacity, most people in developing countries do not have access to these tests. There is a great need for simple, cheap diagnostic tests for STIs that can be performed at the point of care, enabling treatment to be given immediately. It is hoped that recent advances in our understanding of the pathogenesis of these infections, and the availability of the complete genome sequences for each causative organism, will lead to the development of improved point-of-care tests that will reduce the burden of these diseases in developing countries.

Co-ordinate action of bacterial adhesins and human carcinoembryonic antigen receptors in enhanced cellular invasion by capsulate serum resistant Neisseria meningitidis

Neisseria meningitidis (Nm) is a human specific opportunistic pathogen that occasionally penetrates mucosal barriers via the action of adhesins and invasins and evades host immune mechanisms during further dissemination via capsule expression. From in vitro studies, the primary adhesion of capsulate bacteria is believed to be mediated by polymeric pili, followed by invasion via outer membrane adhesins such as Opa proteins. As the latter requires the surface capsule to be down-modulated, invading bacteria would be serum sensitive and thus avirulent. However, there is recent evidence that capsulate bacteria may interact via Opa proteins when host cells express high levels of carcinoembryonic antigen-related cell adhesion molecules (CEACAMs), their target receptors. Such a situation may arise following increased circulation of inflammatory cytokines that upregulate certain adhesion molecules on host cells. In this study, using a tetracycline controlled expression system, we have developed cell lines with inducible CEACAM expression to mimic post-inflammation state of target tissues and analysed the interplay between the three surface components capsule, pili and Opa proteins in cellular interactions. With two distinct cell lines, not only the level but also the rate of adhesion of capsulate Opa-expressing Nm increased concurrently with CEACAM density. Moreover, when threshold levels of receptor were reached, cellular invasion ensued in an Opa-dependent manner. In studies with cell lines intrinsically expressing pilus receptors, notable synergism in cellular interactions between pili and Opa of several meningococcal strains was observed and was independent of capsule type. A number of internalized bacteria were shown to express capsule and when directly isolated from host cells, these bacteria were as serum resistant as the inoculated phenotype. Furthermore, we observed that agents that block Opa-CEACAM binding substantially reduced cellular invasion, while maintaining a low level of cellular adhesion. These studies highlight some of the factors that may determine increased host susceptibility to infection by serum resistant phenotypes; and demonstrate the potential of selective inhibition of key interactions in preventing target tissue penetration while maintaining a level of colonization.

Bacteria targeted by human natural antibodies using alpha-Gal conjugated receptor-specific glycopolymers

Synthesis of polymerizable beta-lactosyl, Galalpha1-->3Gal and alpha-mannosyl acrylamide derivatives with either a hydrophobic aromatic spacer or a hydrophilic biocompatible oligoethoxyl spacer was accomplished. Radical terpolymerizations of beta-lactosyl monomer. alpha-mannosyl monomer, and acrylamide were conducted in aqueous media with ammonium persulfate and N,N,N',N'-tetramethylethylenediamine as initiators. The resulting water soluble glycopolymers were further transformed efficiently by a recombinant alpha1-->3 galactosyltransferase to afford mediators bearing Galalpha1-->3Gal termini as xenoactive antigens and alpha-mannosyl termini as specific ligands for bacterial cells. The binding of the resulting multivalent glycopolymer to bacteria was tested by its ability to inhibit agglutination of yeast to E. coli. The binding of human natural anti-Gal antibodies to the alpha-Gal containing glycopolymers and a monovalent alpha-Gal-Man glycoconjugate was demonstrated by an ELISA inhibition assay.

Cloning and nucleotide sequence analysis of gyrB of Bacillus cereus, B. thuringiensis, B. mycoides, and B. anthracis and their application to the detection of B. cereus in rice

As 16S rRNA sequence analysis has proven inadequate for the differentiation of Bacillus cereus from closely related species, we employed the gyrase B gene (gyrB) as a molecular diagnostic marker. The gyrB genes of B. cereus JCM 2152(T), Bacillus thuringiensis IAM 12077(T), Bacillus mycoides ATCC 6462(T), and Bacillus anthracis Pasteur #2H were cloned and sequenced. Oligonucleotide PCR primer sets were designed from within gyrB sequences of the respective bacteria for the specific amplification and differentiation of B. cereus, B. thuringiensis, and B. anthracis. The results from the amplification of gyrB sequences correlated well with results obtained with the 16S rDNA-based hybridization study but not with the results of their phenotypic characterization. Some of the reference strains of both B. cereus (three serovars) and B. thuringiensis (two serovars) were not positive in PCR amplification assays with gyrB primers. However, complete sequencing of 1.2-kb gyrB fragments of these reference strains showed that these serovars had, in fact, lower homology than their originally designated species. We developed and tested a procedure for the specific detection of the target organism in boiled rice that entailed 15 h of preenrichment followed by PCR amplification of the B. cereus-specific fragment. This method enabled us to detect an initial inoculum of 0.24 CFU of B. cereus cells per g of boiled rice food homogenate without extracting DNA. However, a simple two-step filtration step is required to remove PCR inhibitory substances.

Cloning and nucleotide sequence of the gyrB gene of Vibrio parahaemolyticus and its application in detection of this pathogen in shrimp

Because biochemical testing and 16S rRNA sequence analysis have proven inadequate for the differentiation of Vibrio parahaemolyticus from closely related species, we employed the gyrase B gene (gyrB) as a molecular diagnostic probe. The gyrB genes of V. parahaemolyticus and closely related Vibrio alginolyticus were cloned and sequenced. Oligonucleotide PCR primers were designed for the amplification of a 285-bp fragment from within gyrB specific for V. parahaemolyticus. These primers recognized 117 of 117 reference and wild-type V. parahaemolyticus strains, whereas amplification did not occur when 90 strains of 37 other Vibrio species or 60 strains representing 34 different nonvibrio species were tested. In 100-microliter PCR mixtures, the lower detection limits were 5 CFU for live cells and 4 pg for purified DNA. The possible application of gyrB primers for the routine identification of V. parahaemolyticus in food was examined. We developed and tested a procedure for the specific detection of the target organism in shrimp consisting of an 18-h preenrichment followed by PCR amplification of the 285-bp V. parahaemolyticus-specific fragment. This method enabled us to detect an initial inoculum of 1.5 CFU of V. parahaemolyticus cells per g of shrimp homogenate. By this approach, we were able to detect V. parahaemolyticus in all of 27 shrimp samples artificially inoculated with this bacterium. We present here a rapid, reliable, and sensitive protocol for the detection of V. parahaemolyticus in shrimp.

Vaccines for bacterial sexually transmitted infections: a realistic goal?

Bacterial infections of the genital tract (gonorrhea, chlamydia, chancroid, syphilis) are common and cause significant morbidity. Their importance is heightened by recent appreciation of their roles in facilitation of transmission of the human immunodeficiency virus (HIV). Each is capable of causing repeated infections, suggesting lack of permanent broadly effective immunity. An effective vaccine has yet to be developed for any of these diseases. Rapid progress in understanding the molecular basis for pathogenesis of infection, including mechanisms for escape from otherwise effective immune surveillance and mechanisms for causing injury to host cells, has stimulated renewed efforts to make vaccines for some of these infections. Progress has been greatest for Neisseria gonorrhoeae and Chlamydia trachomatis. Present emphasis is on the major or principal outer membrane proteins of N. gonorrhoeae and C. trachomatis, based on evidence for neutralizing antibodies directed against surface-exposed variable domains of each of these proteins. Other surface-exposed proteins, including the iron-repressible transferrin receptor in gonococci and certain heat-shock proteins in chlamydia, also may be targets for vaccines. Although much remains to be learned, cautious optimism is warranted.

Meningococcal Opa and Opc proteins: their role in colonization and invasion of human epithelial and endothelial cells

Neisseria meningitidis (Nm) isolates from disease or during carriage express, on their outer membranes, one or more of a family of closely related proteins designated Opa proteins. In this study, we have examined the potential roles of Nm Opa proteins in bacterial attachment and invasion of endothelial as well as epithelial cells and compared the influence of Opa proteins with that of Opc protein, which has been previously shown to increase bacterial interactions with eukaryotic cells. Several variants expressing different Opa proteins (A, B, D) or Opc were selected from a culture of capsule-deficient non-piliated bacteria of strain C751. Although the Opa proteins increased bacterial attachment and invasion of endothelial cells, Opc was the most effective protein in increasing bacterial interactions with these cells. In contrast, attachment to several human epithelial cells was facilitated at least as much by OpaB as Opc protein. OpaA was largely without effect whereas OpaD conferred intermediate attachment. OpaB also increased invasion of epithelial cells; more bacteria were internalized by Chang conjunctival cells compared with Hep-2 larynx carcinoma or A549 lung carcinoma cells. Monoclonal antibody reacting with OpaB inhibited bacterial interactions with the host cells. Opa-mediated interactions were also eliminated or significantly reduced in variants expressing capsule or those with sialylated lipopolysaccharide. These data are consistent with the notion that environmental factors controlling capsule and lipopolysaccharide phenotype may modulate bacterial interactions mediated by these OM proteins. In permissive microenvironments, some Opa proteins may be important in bacterial colonization and translocation in addition to Opc. The data also support the notion that Nm Opa may confer tissue tropism.

Expression of the Opc protein correlates with invasion of epithelial and endothelial cells by Neisseria meningitidis

Whereas capsulate strains of Neisseria meningitidis are dependent on pili for adhesion to human endothelial and epithelial cells, strains which lacked assembled pili and were partially capsule-deficient adhered to and invaded human endothelial and epithelial cells if they expressed the Opc protein. Bacteria expressing low or undetectable levels of Opc protein failed to adhere to or invade eukaryotic cells. In addition, the presence of OpaAC751 protein on the surface of bacteria did not increase bacterial interactions with host cells. Association of Opc-expressing bacteria was inhibited by antibodies against Opc. Invasion was dependent on the host-cell cytoskeletal activity and was inhibited by cytochalasin D. In some cells, infected at the apical surface, bacteria emerging from basal surface were detected by electron microscopy. Opc is found in diverse meningococci and may represent a common virulence factor which facilitates adherence and invasion by these bacteria.

Detection of Staphylococcus aureus by polymerase chain reaction amplification of the nuc gene

Synthetic oligonucleotide primers of 21 and 24 bases, respectively, were used in the polymerase chain reaction (PCR) to amplify a sequence of the nuc gene, which encodes the thermostable nuclease of Staphylococcus aureus. A DNA fragment of approximately 270 bp was amplified from lysed S. aureus cells or isolated DNA. The PCR product was detected by agarose gel electrophoresis or Southern blot analysis by using a 33-mer internal nuc gene hybridization probe. With S. aureus cells the lower detection limit was less than 10 CFU, and with the isolated target the lower detection limit was 0.69 pg of DNA. The primers recognized 90 of 90 reference or clinical S. aureus strains. Amplification was not recorded when 80 strains representing 16 other staphylococcal species were tested or when 20 strains representing 9 different nonstaphylococcal species were tested. Some of the non-S. aureus staphylococci produced thermostable nucleases but were PCR negative. The PCR product was generated when in vitro-cultured S. aureus was used to prepare simulated clinical specimens of blood, urine, cerebrospinal fluid, or synovial fluid. No PCR product was generated when the sterile body fluids were tested. However, the sensitivity of the PCR was reduced when S. aureus in blood or urine was tested in comparison with that when bacteria in saline were tested. With the bacteria in blood, the detection limit of the PCR was 10(3) CFU. A positive PCR result was recorded when a limited number of clinical samples from wounds verified to be infected with S. aureus were tested, while the PCR product was not detected in materials from infections caused by other bacteria. Generation of PCR products was not affected by exposure of S. aureus to bactericidal agents, including cloxacillin and gentamicin, prior to testing, but was affected by exposure to UV radiation. The PCR for amplification of the nuc gene has potential for the rapid diagnosis of S. aureus infections by direct testing of clinical specimens, including specimens from patients with ongoing antimicrobial therapy.

Vaccination against gonorrhoea: the potential protective effect of immunization with a synthetic peptide containing a conserved epitope of gonococcal outer membrane protein IB

Monoclonal antibody SM24 recognizes a protective, highly conserved but non-immunogenic epitope on outer membrane protein PIB of Neisseria gonorrhoeae. A series of overlapping synthetic peptides, spanning the deduced amino acid sequence of PIB from strain R10, have been synthesized on solid phase supports. Monoclonal antibody SM24 reacted with two adjacent decapeptides corresponding to residues 191-200 and 196-205, containing the common sequence TYSIP. Following localization of the epitope recognized, a peptide was synthesized corresponding to residues 193-204. The peptide was coupled to a carrier protein (KLH) and both the free peptide and peptide-KLH conjugate were used for immunization of rabbits. The resulting antisera reacted with the immunizing peptide, with denatured PIB on Western blots and, in addition, with native PIB in outer membranes of both the homologous and a heterologous strain. In the presence of human complement the sera were bactericidal for both the homologous and the heterologous strain. Thus synthetic peptides may be used to induce a protective polyclonal immune response against epitopes on gonococcal PI which are normally only weakly or non-immunogenic.

Competition between Neisseria gonorrhoeae and Staphylococcus epidermidis during iron-limited or replete continuous culture

Neisseria gonorrhoeae strain P9-2 was grown in iron-limited or replete continuous culture at a dilution rate of 0.05 h-1, in the presence and absence of Staphylococcus epidermidis. Gonococci maintained expression of pili (P+) and the transparent colony phenotype in pure culture during transitions of iron- and cystine-limited growth. They competed well with staphylococci during iron-limited co-culture and comprised greater than 95% of the population. Transition to cystine-limited growth allowed the staphylococcus to predominate but the gonococcus did not wash out. Furthermore, the gonococcal opaque colony phenotype (O+), indicating synthesis of outer membrane proteins II, was now expressed. Restoration of iron limitation returned the co-culture to its original composition but with P+O+ gonococci dominating. These results suggest that environments might exist in Man where gonococci can compete successfully with normal indigenous bacteria during infection.

The role of Bacteroides gingivalis in periodontal disease

The microbial flora in adult advanced periodontitis lesions is comprised of Gram-negative rods, with Bacteroides gingivalis as one of the major representatives. This review deals with biological properties of surface antigens, hemagglutinin (attachment factor), and capsular structure of B. gingivalis. Sera containing high IgG antibody levels to B. gingivalis enhanced the complement-mediated bactericidal activity in vitro, although the susceptibility to complement-mediated lysis differed among B. gingivalis strains. The protective effect of immunization against B. gingival is infection was examined in hamsters in which cotton threads had been tied to the gingival margins of the mandibular first molar. Repeated oral topical application of hyper-immune sera against B. gingivalis resulted in effective elimination of the organisms from the periodontal lesions in the experimental animals.

Vaccination against infectious bovine keratoconjunctivitis: protective efficacy and antibody response induced by pili of homologous and heterologous strains of Moraxella bovis

The protective effect of 2 Moraxella bovis pili vaccines against infectious bovine keratoconjunctivitis (IBK) experimentally induced by homologous or heterologous strain challenge with virulent, haemolytic M. bovis strain, Dal 2d, was measured in trials using weaned calves aged 3 to 7 months. Purified pili vaccines were prepared from haemolytic strain Dal 2d, (pilus serogroup IV), and haemolytic strain Epp 63, (pilus serogroup III). Calves were challenged by conjunctival instillation of 1 x 10(9) colony forming units of virulent M. bovis strain Dal 2d 14 days after the second of 2 subcutaneous doses of vaccine. Each consisted of 200 micrograms of pili in alum-oil adjuvant administered at an interval of 21 days. In trial 1 the level of protection against challenge with the homologous strain was 46.7% (p less than 0.01). Small, rapidly resolving lesions of IBK occurred in some vaccinates compared with a larger proportion of severe lesions that required treatment in non-vaccinated calves (p less than 0.025). In trial 2, the level of protection against IBK after exposure of vaccinates to the homologous Dal 2d strain was 72.7%, but no significant level of protection or reduction in the size and duration of lesions was apparent in similarly challenged calves vaccinated with Epp 63 pili when contrasted with susceptible, non-vaccinated controls. No marked reduction in the duration of infection with M. bovis Dal 2d following challenge resulted from vaccination with pili of either of the serogroups III or IV. Rising homologous serum IgG antibody titres to serogroups III and IV pili were recorded in response to vaccination with each antigen.(ABSTRACT TRUNCATED AT 250 WORDS)

Protective efficacy of active and passive immunizations against experimental infection with Bacteroides gingivalis in ligated hamsters

The protective efficacy of immunization against Bacteroides gingivalis infection was examined in hamsters. Whole cells or extracted hemagglutinin of B. gingivalis 381 was injected with incomplete Freund adjuvant into the inguinal regions of hamsters. Two weeks after the rats received a booster injection, cotton threads were tied coronally to the gingival margins of the mandibular first molars, and then a streptomycin-resistant B. gingivalis 381R' strain was inoculated into the rats' oral cavities. The subcutaneous immunizations resulted in slight reductions in the numbers of B. gingivalis on the ligature threads compared with the sham-immunized group. Peroral administration of whole cells of B. gingivalis to hamsters elicited salivary immunoglobulin responses, but no reduction of B. gingivalis 381R' colonization was found in this group. Repeated passive immunizations with rabbit antiserum to B. gingivalis into the oral cavities of the hamsters resulted in a reduction in the number of organisms in the periodontal region.

Antigenic and immunogenic properties of cyanogen bromide peptides from gonococcal outer membrane protein IB. Evidence for the existence of a surface-exposed conserved epitope

Two distinct species of gonococcal porin proteins exist that differ with regard to surface exposure. Protein IB, expressed by strains of the WII/III serogroup, has both termini buried in the outer membrane, leaving a central region of the molecule exposed at the cell surface. We have attempted to define this region of protein IB in detail by studying the antigenic and immunogenic properties of peptides derived from protein IB. Treatment of gonococcal protein IB (serotype 5) with cyanogen bromide resulted in cleavage of protein IB into three major fragments of Mr of 15,000, 13,000, and 8,000. The location of these peptides in the intact protein was determined by analysis of partial cleavage products. The 8,000 Mr peptide (CB2) was found to be located in the central region of the protein. Chymotrypsin cleavage of protein IB revealed a cleavage site near one of the cyanogen bromide cleavage sites. Trypsin was found to cleave the protein, either in outer membranes complexes (OMC) or in detergent micelles, in the central CB2 fragment. These results suggest that CB2 is a part of the surface-exposed region of protein IB. Immunization of mice with purified protein IB (serotype 5) induced antibodies against all three CB-peptides. Absorption of the sera with homologous OMC resulted in a complete removal of antibodies against CB2, supplying further evidence for its surface-exposed nature. Antibodies against the 13,000 Mr peptide (CB1) could not be absorbed with intact OMC, suggesting that this peptide is buried within the outer membrane. Antisera raised against CB2 of serotype 5 demonstrated a considerable cross-reactivity with heterologous outer membranes. On the contrary, intact OMC induced mainly type-specific antibodies. These data demonstrate the presence of conserved epitopes on the surface-exposed CB2 peptide. These conserved epitopes are generally not very immunogenic when present in intact OMC.

Immunobiology of gonococcal outer membrane protein I

Monoclonal antibodies have been obtained which react with gonococcal outer membrane protein I. One antibody recognised the majority of strains expressing P.IA and another recognised the majority of strains expressing P.IB. In in vitro tests both antibodies were bactericidal in the presence of complement, opsonic for phagocytosis by human PMN and protected epithelial cells against gonococcal invasion. Thus conserved epitopes on P.I. are potentially effective targets for immunoprophylaxis.