Attachment role of gonococcal pili. Optimum conditions and quantitation of adherence of isolated pili to human cells in vitro

Neisseria gonorrhoeae physiology and pathogenesis

Neisseria gonorrhoeae is an obligate human pathogen that is the cause of the sexually transmitted disease gonorrhoea. Recently, there has been a surge in gonorrhoea cases that has been exacerbated by the rapid rise in gonococcal multidrug resistance to all useful antimicrobials resulting in this organism becoming a significant public health burden. Therefore, there is a clear and present need to understand the organism's biology through its physiology and pathogenesis to help develop new intervention strategies. The gonococcus initially colonises and adheres to host mucosal surfaces utilising a type IV pilus that helps with microcolony formation. Other adhesion strategies include the porin, PorB, and the phase variable outer membrane protein Opa. The gonococcus is able to subvert complement mediated killing and opsonisation by sialylation of its lipooligosaccharide and deploys a series of anti-phagocytic mechanisms. N. gonorrhoeae is a fastidious organism that is able to grow on a limited number of primary carbon sources such as glucose and lactate. The utilization of lactate by the gonococcus has been implicated in a number of pathogenicity mechanisms. The bacterium lives mainly in microaerobic environments and can grow both aerobically and anaerobically with the aid of nitrite. The gonococcus does not produce siderophores for scavenging iron but can utilize some produced by other bacteria, and it is able to successful chelate iron from host haem, transferrin and lactoferrin. The gonococcus is an incredibly versatile human pathogen; in the following chapter, we detail the intricate mechanisms used by the bacterium to invade and survive within the host.

Epithelial Haven and Autophagy Breakout in Gonococci Infection

The World Health Organization (WHO) has estimated that in 2016, there were 87 million new cases of gonorrhea. Gonorrhea is caused by the sexually transmitted human-exclusive agent Neisseria gonorrhoeae, a Gram-negative diplococcus that causes cervicitis in females and urethritis in males and may lead to more severe complications. Currently, there is no vaccine against N. gonorrhoeae. Its resistance to antibiotics has been increasing in the past few years, reducing the range of treatment options. N. gonorrhoeae requires a surface protein/receptor (Opa proteins, porin, Type IV pili, LOS) to adhere to and invade epithelial cells. During invasion and transcytosis, N. gonorrhoeae is targeted by the autophagy pathway, a cellular maintenance process which balances sources of energy at critical times by degrading damaged organelles and macromolecules in the lysosome. Autophagy is an important host defense mechanism which targets invading pathogens. Based on transmission electron microscopy (TEM) analysis, the intracellular bacteria occupy the autophagosome, a double-membraned vesicle that is formed around molecules or microorganisms during macroautophagy and fuses with lysosomes for degradation. Most of the gonococci end up in autolysosomes for degradation, but a subpopulation of the intracellular bacteria inhibits the maturation of the autophagosome and its fusion with lysosomes by activating mTORC1 (a known suppressor of the autophagy signaling), thus escaping autophagic elimination. This mini review focuses on the cellular features of N. gonorrhoeae during epithelial cell invasion, with a particular focus on how N. gonorrhoeae evades the autophagy pathway.

Neisseria gonorrhoeae host adaptation and pathogenesis

The host-adapted human pathogen Neisseria gonorrhoeae is the causative agent of gonorrhoea. Consistent with its proposed evolution from an ancestral commensal bacterium, N. gonorrhoeae has retained features that are common in commensals, but it has also developed unique features that are crucial to its pathogenesis. The continued worldwide incidence of gonorrhoeal infection, coupled with the rising resistance to antimicrobials and the difficulties in controlling the disease in developing countries, highlights the need to better understand the molecular basis of N. gonorrhoeae infection. This knowledge will facilitate disease prevention, surveillance and control, improve diagnostics and may help to facilitate the development of effective vaccines or new therapeutics. In this Review, we discuss sex-related symptomatic gonorrhoeal disease and provide an overview of the bacterial factors that are important for the different stages of pathogenesis, including transmission, colonization and immune evasion, and we discuss the problem of antibiotic resistance.

Identification and Characterization of Serotype-Specific Variation in Group A Streptococcus Pilus Expression

Isolates of a given bacterial pathogen often display phenotypic variation, and this can negatively impact public health, for example, by reducing the efficacy of preventative measures. Here, we identify that the human pathogen group A Streptococcus (GAS; Streptococcus pyogenes) expresses pili on its cell surface in a serotype-specific manner. Specifically, we show that serotype M3 GAS isolates, which are nonrandomly associated with causing particularly severe and lethal invasive infections, produce negligible amounts of pili relative to serotype M1 and M49 isolates. Performance of an interserotype transcriptome comparison (serotype M1 versus serotype M3) was instrumental in this discovery. We also identified that the transcriptional regulator Nra positively regulates pilus expression in M3 GAS isolates and that the low level of pilus expression of these isolates correlates with a low level of nra transcription. Finally, we discovered that the phenotypic consequences of low levels of pilus expression by M3 GAS isolates are a reduced ability to adhere to host cells and an increased ability to survive and proliferate in human blood. We propose that an enhanced ability to survive in human blood, in part due to reduced pilus expression, is a contributing factor in the association of serotype M3 isolates with highly invasive infections. In conclusion, our data show that GAS isolates express pili in a serotype-dependent manner and may inform vaccine development, given that pilus proteins are being discussed as possible GAS vaccine antigens.

Molecular and Morphometric Characterization of Acanthamoeba spp. from Different Water Sources of Northwest Iran as a Neglected Focus, Co-Bordered With the Country of Iraq

Background

Acanthamoeba spp. is a free-living opportunistic protozoan parasites, which can be found in tap, fresh and bottled mineral waters, contact lens solutions, soil etc.

Objectives

The present study is aimed to determine the Acanthamoeba spp. on the basis of their morpho-molecular aspects in different water sources of the West Azerbaijan province, Northwest of Iran.

Methods

In this cross-sectional study, 60 water samples were collected from rivers and tap waters during June to September 2015. The water samples were filtered through a cellulose nitrate filter and cultured on non-nutrient agar medium. The extracted DNAs were amplified and some ampliqons were sequenced using partial 18S rRNA for genotyping and phylogenetic analyses.

Results

Twenty-seven (45%) out of 60 water samples were positive to Acanthamoeba spp. using both culture and morphological examinations. In addition, 24 (40%) out of 27 positive samples in culture method were confirmed by PCR to be Acanthamoeba spp.

Conclusions

A relatively high prevalence of Acanthamoeba spp. in rivers reflects a risk alert for threatening human health in the region. However, well hygienic status of the tap waters considering Acanthamoeba spp. cannot be ignored in western co-border regions of Iran-Iraq. This study can also serve as a platform for further explorations of water sources in Iran and neighboring countries.

Gonorrhea - an evolving disease of the new millennium

Etiology, transmission and protection: Neisseria gonorrhoeae (the gonococcus) is the etiological agent for the strictly human sexually transmitted disease gonorrhea. Infections lead to limited immunity, therefore individuals can become repeatedly infected. Pathology/symptomatology: Gonorrhea is generally a non-complicated mucosal infection with a pustular discharge. More severe sequellae include salpingitis and pelvic inflammatory disease which may lead to sterility and/or ectopic pregnancy. Occasionally, the organism can disseminate as a bloodstream infection. Epidemiology, incidence and prevalence: Gonorrhea is a global disease infecting approximately 60 million people annually. In the United States there are approximately 300, 000 cases each year, with an incidence of approximately 100 cases per 100,000 population. Treatment and curability: Gonorrhea is susceptible to an array of antibiotics. Antibiotic resistance is becoming a major problem and there are fears that the gonococcus will become the next "superbug" as the antibiotic arsenal diminishes. Currently, third generation extended-spectrum cephalosporins are being prescribed. Molecular mechanisms of infection: Gonococci elaborate numerous strategies to thwart the immune system. The organism engages in extensive phase (on/off switching) and antigenic variation of several surface antigens. The organism expresses IgA protease which cleaves mucosal antibody. The organism can become serum resistant due to its ability to sialylate lipooligosaccharide in conjunction with its ability to subvert complement activation. The gonococcus can survive within neutrophils as well as in several other lymphocytic cells. The organism manipulates the immune response such that no immune memory is generated which leads to a lack of protective immunity.

Neisseria gonorrhoeae pilus attenuates cytokine response of human fallopian tube explants

Background. A role for pilus during attachment of Neisseria gonorrhoeae to epithelia of the female reproductive tract is currently assumed. However, Pil⁻ gonococci have been observed during infection of the reproductive tract, which prompted us to examine the effect of pili on the dynamics of infection and the inflammatory responses of mucosal explants of the human Fallopian tube. Methods. Mucosal explants were infected in vitro with Opa negative Pil⁻ and Pil⁺N. gonorrhoeae strains. Results. Piliation enhanced gonococcal adherence to the epithelium within 3 h of infection (P < 0.05) but thereafter did not offer advantage to gonococci to colonize the epithelial cell surface (P > 0.05). No differences were found between the strains in numbers of gonococci inside epithelial cells. Pil⁻ bacteria induced higher levels (P < 0.05) of IL-1β, TNF-α, GM-CSF, MCP-1, and MIP-1β than Pil⁺ bacteria. There were no differences between both strains in LOS pattern, and Pil expression did not change after coincubation with mucosal strips. Conclusions. Results show that gonococcal invasion of the human Fallopian tube can occur independently of pilus or Opa expression, and suggest that pilus, by inhibition of several key elements of the initial inflammatory response, facilitates sustained infection of this organ.

Current concepts in bacterial sexually transmitted diseases

Sexually transmitted diseases (STDs) are the most common infectious diseases worldwide, with over 350 million new cases occurring each year, and have far-reaching health, social, and economic consequences. Failure to diagnose and treat STDs at an early stage may result in serious complications and sequelae. STDs are passed from person to person primarily by sexual contact and are classified into varied groups. Some cause mild, acute symptoms and some are life-threatening. They are caused by many different infectious organisms and are treated in different ways. Syphilis and gonorrhea are ancient afflictions. Now, however, Chlamydia is prevalent and has become the most common bacterial STD. Antimicrobial resistance of several sexually transmitted pathogens is increasing, rendering some regimens ineffective, adding to therapeutic problems. A standardized treatment protocol for STDs is recommended to ensure that all patients receive adequate treatment. Appropriate treatment of STDs is an important public health measure.

Factors that influence the rate of epithelial maturation in the cervix in healthy young women

PURPOSE

To examine the longitudinal changes in the epithelial topography of the cervix in healthy young women; and to determine the sociodemographic, behavioral, and biological factors associated with the rate of cervical epithelial maturation.

METHODS

Healthy young women were enrolled from October 2000 to September 2002 as part of a larger study of human papillomavirus (HPV). At interval visits, interviews, infection testing, and colpophotography (3% acetic acid; 10x, 16x magnifications) were performed. Areas of total cervical face and cervical immaturity, defined as columnar and early squamous metaplasia, were quantitatively measured using computerized planimetry. Cervical immaturity was expressed as percentage of total cervical face. This analysis includes the first consecutive 145 women with greater than 10% immaturity at baseline. The rate of cervical maturation was defined as change in percent-immaturity. Predictors included sociodemographics, sexual behaviors, and infections. Data analyses included multivariate generalized linear models with repeated measures.

RESULTS

The baseline mean age was 17.8 years. Colpophotographs were available from 815 total visits, representing 2.7 years mean follow-up per woman and 5.9-month mean intervals. Women began the study with a median of 39% immaturity and ended with 8% immaturity. After adjusting for time and baseline percent-immaturity, an increased rate of cervical maturation was associated with oral contraceptive pill use (parameter estimate -.023, p =.04) and smoking (-.039, p =.01).

CONCLUSIONS

Cervical maturation was documented during relatively short time periods for the vast majority of these women. Oral contraceptive pills and smoking may accelerate the maturational process, representing increased cell proliferation and thus a possible greater vulnerability to HPV.

Adhesion of Neisseria gonorrhoeae and disease

Adhesion of gonococci to mucosal epithelial cells appear to be a critical step in the pathogenesis of gonococcal infection. Parameters affecting adhesion, the antigens involved in adhesion and the human antibody response that blocks adhesion have been studied. Gonococci adhere to a variety of human cells grown either in tissue culture or organ culture or scraped from mucosal surfaces. They adhere in greatest number to mucosal cells derived from sites of natural infection but buccal mucosal cells were used for most of these studies because of the ease of obtaining them, the homogeneous population obtained, and the similarity of the results of antibody studies with all cell types. The ability of a given strain of gonococci to attach to buccal cells (receptors) varied with the individual from whom the cells were obtained, and the capacity to support adhesion of a given strain fluctuated from day to day. The principal antigens mediating attachment are pili (filamentous protein appendages extending from the bacterial cell wall) which are antigenically heterogeneous. Lipopolysaccharide also blocks attachment but it is less efficient than pili and is not species-specific. Other antigens, probably proteins, also block attachment. Human antibody (both local and humoral) blocked the adhesion of gonococci. The antibody was directed against pili and the antigens in naturally occurring disease and could be induced by immunizing subjects with purified pili. The results of these studies suggest two new approaches to the prevention of gonorrhoea: (1) (competitive) inhibition of the adhesion with specific antigens, i.e. pili; and (2) immunization with purified attachment antigens to produce shielding antibodies.

The cytotoxic fimbrial structural subunit of Xenorhabdus nematophila is a pore-forming toxin

We have purified a fimbrial shaft protein (MrxA) of Xenorhabdus nematophila. The soluble monomeric protein lysed larval hemocytes of Helicoverpa armigera. Osmotic protection of the cells with polyethylene glycol suggested that the 17-kDa MrxA subunit makes pores in the target cell membrane. The internal diameter of the pores was estimated to be >2.9 nm. Electron microscopy confirmed the formation of pores by the fimbrial subunit. MrxA protein oligomerized in the presence of liposomes. Electrophysiological studies demonstrated that MrxA formed large, voltage-gated passive-diffusion channels in lipid bilayers.

Insecticidal pilin subunit from the insect pathogen Xenorhabdus nematophila

Xenorhabdus nematophila is an insect pathogen and produces protein toxins which kill the larval host. Previously, we characterized an orally toxic, large, outer membrane-associated protein complex from the culture medium of X. nematophila. Here, we describe the cloning, expression, and characterization of a 17-kDa pilin subunit of X. nematophila isolated from that protein complex. The gene was amplified by PCR, cloned, and expressed in Escherichia coli. The recombinant protein was refolded in vitro in the absence of its cognate chaperone by using a urea gradient. The protein oligomerized during in vitro refolding, forming multimers. Point mutations in the conserved N-terminal residues of the pilin protein greatly destabilized its oligomeric organization, demonstrating the importance of the N terminus in refolding and oligomerization of the pilin subunit by donor strand complementation. The recombinant protein was cytotoxic to cultured Helicoverpa armigera larval hemocytes, causing agglutination and subsequent release of the cytoplasmic enzyme lactate dehydrogenase. The agglutination of larval cells by the 17-kDa protein was inhibited by several sugar derivatives. The biological activity of the purified recombinant protein indicated that it has a conformation similar to that of the native protein. The 17-kDa pilin subunit was found to be orally toxic to fourth- or fifth-instar larvae of an important crop pest, H. armigera, causing extensive damage to the midgut epithelial membrane. To our knowledge, this is first report describing an insecticidal pilin subunit of a bacterium.

Acid stress upregulated outer membrane proteins in clinical isolates ofNeisseria gonorrhoeae, but not most commensalNeisseria

Human immune serum recognition of outer membrane components from commensal and pathogenic Neisseria cultured under neutral and acidic conditions was investigated. Acid stress caused no detectable alterations in lipooligosaccharide migration and (or) staining, in outer membrane protein profiles, or in immune serum recognition of outer membrane components from Neisseria mucosa or Neisseria sicca. There was also no difference in the lipoologosaccharide electrophoretic pattern of acid- and neutral-grown Neisseria lactamica, but there were differences in outer membrane protein expression. The outer membrane protein alterations induced by acid stress in N. lactamica were not the same as those seen in isolates from patients with uncomplicated gonococcal infection, pelvic inflammatory disease, and disseminated gonococcal infection. Many differences were detected in the immune serum recognition of outer membrane components from acid- and neutral-cultured N. lactamica and from the clinical isolates of Neisseria gonorrhoeae, and these should be considered in vaccine design.Key words: Neisseria gonorrhoeae, commensal Neisseria, acid stress, outer membrane proteins.

Interactions of pathogenic neisseriae with epithelial cell membranes

The closely related bacterial pathogens Neisseria gonorrhoeae (gonococci, GC) and N. meningitidis (meningococci, MC) initiate infection at human mucosal epithelia. Colonization begins at apical epithelial surfaces with a multistep adhesion cascade, followed by invasion of the host cell, intracellular persistence, transcytosis, and exit. These activities are modulated by the interaction of a panoply of virulence factors with their cognate host cell receptors, and signals are sent from pathogen to host and host to pathogen at multiple stages of the adhesion cascade. Recent advances place us on the verge of understanding the colonization process at a molecular level of detail. In this review we describe the Neisseria virulence factors in the context of epithelial cell biology, placing special emphasis on the signaling functions of type IV pili, pilus-based twitching motility, and the Opa and Opc outermembrane adhesin/invasin proteins. We also summarize what is known about bacterial intracellular trafficking and growth. With the accelerated integration of tools from cell biology, biochemistry, biophysics, and genomics, experimentation in the next few years should bring unprecedented insights into the interactions of Neisseriae with their host.

An Immunodominant Conserved Region Within the Variable Domain of VlsE, the Variable Surface Antigen of Borrelia burgdorferi

Antigenic variation is an effective strategy evolved by pathogenic microbes to avoid immune destruction. Variable Ags such as the variable major protein of Borrelia hermsii, the variant surface glycoprotein of African trypanosomes, and the pilin of Neisseria gonorrhoeae include an immunodominant variable domain and one or more invariable domains that are not antigenic. Short, nonantigenic, invariable regions also may be present within the variable domain. VlsE (variable major protein-like sequence, expressed), the variable surface Ag of Borrelia burgdorferi, the Lyme disease spirochete, also contains both variable and invariable domains. In addition, interspersed within the VlsE variable domain there are six invariable regions (IR1–6) that together amount to half of this portion’s primary structure. We show here that these IRs are conserved among strains and genospecies of the B. burgdorferi sensu lato complex. Surprisingly, unlike the invariable regions of variable major protein, variant surface glycoprotein, and pilin, which are not antigenic in natural infections, the most conserved of the IRs, IR6, is immunodominant in Lyme disease patients and in monkeys infected with B. burgdorferi. IR6 is exposed on the surface of VlsE, as assessed by immunoprecipitation experiments, but is inaccessible to Ab on the spirochete’s outer membrane, as demonstrated by immunofluorescence and in vitro killing assays. VlsE thus significantly departs from the antigenic variation paradigm, whereby immunodominance is only manifest in variable portions. We submit that IR6 may act as a decoy epitope(s) and contribute to divert the Ab response from other, perhaps protective regions of VlsE.

Transferrin increases adherence of iron-deprived Neisseria gonorrhoeae to human endometrial cells

OBJECTIVE

Our purpose was to study the effects of iron deprivation with and without human transferrin supplementation on the adherence and invasion of Neisseria gonorrhoeae to human endometrial cells.

STUDY DESIGN

N. gonorrhoeae grown with our without iron was placed in media alone or media containing 2.5 mg/ml saturated human transferrin or unsaturated transferrin. N. gonorrhoeae was inoculated onto polarized human endometrial carcinoma cell (HEC 1-B) monolayers, and at various intervals monolayers were washed and incubated with media containing gentamicin or media alone. Colony-forming units per milliliter of N. gonorrhoeae associated with HEC 1-B cells were then determined. N. gonorrhoeae strains tested included both a transferrin receptor-positive (wild-type) and a transferrin receptor-negative mutant. Differences in percent of original inoculum remaining at varying time points were analyzed by the Mann-Whitney U test. Transmission electron microscopy using a primary endometrial cell line was used to verify findings.

RESULTS

Iron-negative N. gonorrhoeae exhibited less adherence than did iron-positive N. gonorrhoeae. No difference in HEC 1-B adherence was seen when either saturated transferrin or unsaturated transferrin was added to the iron-positive N. gonorrhoeae. With iron-negative N. gonorrhoeae addition of either saturated transferrin or unsaturated transferrin significantly increased N. gonorrhoeae adherence although unsaturated transferrin did not permit growth of iron-negative N. gonorrhoeae in tissue culture media alone. Transmission electron microscopy confirmed increased adherence of iron-negative N. gonorrhoeae supplemented with unsaturated transferrin. An iron-negative N. gonorrhoeae mutant lacking the transferrin receptor exhibited no adherence regardless of addition of saturated transferrin or unsaturated transferrin. Invasion could not be quantitated reliably because of persistence of gentamicin effect.

CONCLUSION

Iron and transferrin increased attachment of N. gonorrhoeae to human endometrial cells.

Sequence changes in the pilus subunit lead to tropism variation of Neisseria gonorrhoeae to human tissue

Pili of Neisseria gonorrhoeae are correlated with increased bacterial attachment to epithelial cells and undergo both phase and antigenic variation. Phase variation of gonococcal pili can be brought about by recombination events in the pilin structural gene, pilE, or by the on/off switch in expression of PilC, a pilus biogenesis protein for which two loci exist. We have studied the binding to epithelial cell lines and to fixed tissue sections of N. gonorrhoeae MS11 derivatives and mutants carrying structurally defined PilE and PilC proteins. In situ binding studies of N. gonorrhoeae to formalin-fixed tissue sections resulted in a binding pattern similar to that obtained using viable epithelial cell lines of different origin. Piliated gonococcal clones, containing different pilE sequences, varied dramatically from one another in their efficiencies at binding to corneal and conjunctival tissue, but bound equally well to cervical and endometrial tissues. Further, the binding data suggested that PilC expression by itself, i.e. without pili, cannot confer bacterial binding and that expression of either PilC1 or PilC2 does not confer different binding properties to the bacterial cells. Possible receptors for piliated gonococci were expressed in human tissues, such as cervix, endometrium, cornea, intestine, stomach, mid-brain and meninges, but not in human kidney. Pretreatment of the target tissues with Proteinase K decreased the gonococcal binding dramatically, whereas pretreatment with neuraminidase and meta-periodate, which cleave carbon-carbon linkages between vicinal hydroxyl groups in carbohydrates, did not affect attachment of gonococci. These data argue that pilus-dependent attachment of N. gonorrhoeae to human tissue may be mediated by a eukaryotic receptor having protein characteristics, and that the pilus subunit sequence may play an important role in the interaction with human cornea.

Type IV prepilin peptidase gene of Neisseria gonorrhoeae MS11: presence of a related gene in other piliated and nonpiliated Neisseria strains

The assembly of type IV pili in Neisseria gonorrhoeae is a complex process likely to require the products of many genes. One of these is the enzyme prepilin peptidase, which cleaves and then N methylates the precursor pilin subunits prior to their assembly into pili. We have used a PCR amplification strategy to clone the N. gonorrhoeae prepilin peptidase gene, pilDNg. A single copy of the gene is shown to be present in the chromosome. Its product promotes correct cleavage of the gonococcal prepillin in Escherichia coli cells carrying both the prepilin peptidase gene and the pilin structural gene. PilDNg also cleaves prePulG, a type IV pilin-like protein of Klebsiella oxytoca. Moreover, PilDNg complements a mutation in the gene coding for the prepilin peptidase-like protein of K. oxytoca, pulO, partially restoring PulG-PulO-dependent extracellular secretion of the enzyme pullulanase. Finally, we show that genes homologous to pilDNg are present and expressed in a variety of species in the genus Neisseria, including some commensal strains.

Phase variation of gonococcal pili by frameshift mutation in pilC, a novel gene for pilus assembly

Pili prepared from Neisseria gonorrhoeae contain minor amounts of a 110 kd outer membrane protein denoted PilC. The corresponding gene exists in two copies, pilC1 and pilC2, in most strains of N.gonorrhoeae. In the piliated strain MS11(P+), only one of the genes, pilC2, was expressed. Inactivation of pilC2 by a mTnCm insertion resulted in a nonpiliated phenotype, while a mTnCm insertion in pilC1 had no effect on piliation. Expression of pilC was found to be controlled at the translational level by frameshift mutations in a run of G residues positioned in the region encoding the signal peptide. Nonpilated (P-), pilin expressing colony variants that did not express detectable levels of PilC were selected; all P+ backswitchers from these P-, PilC- clones were found to be PilC+. The structural gene for pilin, pilE, was sequenced and found to be identical in one P-, PilC- and P+, PilC+ pair. Most PilC- cells were completely bald whereas the PilC+ backswitcher had 10-40 pili per cell. Thus, a turn ON and turn OFF in the expression of PilC results in gonococcal pili phase variation. These results suggest that PilC is required for pilus assembly and/or translocation across the gonococcal outer membrane.

Identification and characterization of peptidoglycan-associated proteins in Neisseria gonorrhoeae

The principal proteins associated with Neisseria gonorrhoeae peptidoglycan (PG), as identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, are the following: two proteins at approximately 90 kilodaltons (kDa), single major species at both 60 and 44 kDa, a 34- to 36-kDa protein, and three proteins between 28 and 32 kDa. A protein analogous to Escherichia coli Braun lipoprotein was not detected with gonococcal cell wall preparations. The identity of the PG-associated proteins was confirmed immunologically with antibody generated against purified cell walls. Two types of protein species, dithiothreitol extractable (the majority) and alkylation dependent (primarily the 34- to 36-kDa protein), appeared to be associated with the N. gonorrhoeae cell wall fraction. It was found that a crucial step in the extraction of the proteins from the PG fraction was the inclusion of an acetone-water wash of the purified PG pellet. Studies with cell wall preparations obtained from N. gonorrhoeae intrinsically labeled with 32P revealed that the acetone wash was removing phospholipid from the cell wall fraction and thus facilitating protein extraction. Autoradiographic analysis with PG material derived from 125I-surface-labeled cells indicated that the 44-kDa protein is exposed on the surface of the organism even when associated with the PG layer. Radioimmunoprecipitation with anti-PG antibody confirmed these findings. Lectin analysis (wheat germ agglutinin conjugated to horseradish peroxidase) suggested that the 34- to 36-kDa protein is covalently attached to the PG layer.

Interaction of non-piliated Neisseria gonorrhoeae strain 7122 and protein IA with an epithelial cell monolayer

Studies with [14C] uracil-labelled bacteria revealed that the interaction of Neisseria gonorrhoeae with epithelial cells occurred in a time-dependent reaction which is slightly pH-dependent and optimal at pH 6.5. Immunofluorescence tests and immunoelectron microscopy of ultrathin sections confirmed the attachment of these bacteria to the epithelial cell membrane. The interaction of purified protein I with epithelial cells was time-dependent and reached equilibrium after four hours as shown by tracer experiments with 125I-labeled protein I. Cleavage experiments with trypsin followed by SDS-PAGE and autoradiography indicated that protein I (labeled with 125I) was associated with the membrane of the epithelial cells and only partly accessible by trypsin after its interaction with these mammalian cells. Immunofluorescence tests as well as immunoelectron microscopy with the monoclonal antibody G7A2C and gold-labeled protein A confirmed a dense association pattern of protein I with the cell monolayer.

Gonococcal and meningococcal pathogenesis as defined by human cell, cell culture, and organ culture assays

Human cells, cell cultures, and organ cultures have been extremely useful for studying the events that occur when gonococci and meningococci encounter human mucosal surfaces. The specificity and selectivity of these events for human cells are striking and correlate with the adaptation of these pathogens for survival on human mucous membranes. To colonize these sites, meningococci and gonococci have developed mechanisms to damage local host defenses such as the mucociliary blanket, to attach to epithelial cells, and to invade these cells. Attachment to epithelial cells mediated by pili, and to some types of cells mediated by PIIs, serves to anchor the organism close to sources of nutrition and allows multiplication. Intracellular invasion, possibly initiated by the major porin protein, may provide additional nutritional support and protection from host defenses. Mucosal invasion may also result in access of gonococci and meningococci to the bloodstream, leading to dissemination.

Surface immunolabeling of Neisseria gonorrhoeae employing monoclonal antibodies to proteins IA and IB

The technique of immunomarking intact bacteria with monoclonal antibodies (MAb) and gold-labeled anti-IgG provides a rapid and reliable method for localization of surface-exposed antigens. Cell suspensions of Neisseria gonorrhoeae were incubated with monoclonal antibodies directed against different epitopes of protein I as shown by ELISA inhibition test (unpublished data). The bound IgG molecules were detected with gold labeled anti-mouse IgG or protein A. MAbs against various epitopes of protein I showed differences in their reaction pattern with intact bacteria. We compared the results achieved by the gold immunomarking technique with coagglutination (CoA) and immunofluorescence (IF) tests. The results of the three methods correlated for some antibodies and were ambiguous for other MAbs. The advantage of the immunogold method over immunofluorescence and coagglutination is that distribution and localization of antigen on the surface of gonococci can be exactly determined using electron microscopy.

Effects of recA mutations on pilus antigenic variation and phase transitions in Neisseria gonorrhoeae

Intragenic recombination between the single complete pilin gene (expression locus) and multiple, distinct, partial pilin gene copies (silent, storage loci) is thought to account for the generation of pilus antigenic diversity and piliation phase (on-off) changes exhibited by Neisseria gonorrhoeae. The mechanisms operating in the genomic rearrangements associated with these forms of pilus variation were investigated through the study of isogenic strains of gonococci bearing either wild-type or altered recA alleles. Examination of the rates of pilus phase variation and the genetic basis for changes in piliation status displayed by these strains show that recA mediated homologous recombination is required for these high frequency events and confirm that the nonpiliated state results from mutations in the expressed pilin gene. In a strain that is deficient in recA mediated homologous recombination, pilus phase variation occurs at a 100-1000-fold reduced rate and results predominantly from one class of spontaneous frameshift mutations within the pilin structural gene.

Current and Future Applications of Monoclonal Antibodies against Bacteria in Veterinary Medicine

This chapter discusses the current and future applications of monoclonal antibodies against bacteria in veterinary medicine. It discusses the existing applications of monoclonal antibodies, including the use of pilus-specific monoclonal antibodies for passive immunization of calves and piglets against enteropathogenic E. coli (EPEC) infections as well as the development of rapid diagnostic test kits for field diagnosis of EPEC infections. The potential applications of monoclonal antibodies for passive immunization against a variety of veterinary pathogens are passive immunization against Moraxella bovis (pinkeye), Bacteroides nodosus (foot rot), EPEC enterotoxin (enteric colibacillosis), Pasteurella haemolytica (pneumonic pasteurellosis), and Streptococcus equi (strangles). Three main areas of application for monoclonal antibodies against bacterial antigens in veterinary medicine are passive immunization, improved immunodiagnostics, and immunotherapy. Monoclonal antibodies, because of their specificity, unlimited availability, and high titer, represent excellent passive immunizing agents. However, their potential usefulness in preventing infection must be evaluated on a case-by-case basis.

Pili of Neisseria meningitidis. Analysis of structure and investigation of structural and antigenic relationships to gonococcal pili

To provide information useful for the design of a pilus vaccine effective for the prevention of both meningococcal and gonococcal disease, the electron microscopic morphology of meningococcal pili and the structural and antigenic relationships of meningococcal pili to gonococcal pili were investigated. Meningococcal pili were 4-6 nm in width, extended 500-6,000 nm from the organism surface, and occurred singly or in bundles composed of 8-10 pili per bundle. Meningococcal pilin varied between 17,250 and 20,600 daltons. Pilin was present in outer membrane preparations of some meningococcal isolates that were nonpiliated by electron microscopic examination. Antibodies to gonococcal pili, cyanogen bromide cleavage fragments of gonococcal pilin, or synthetic peptide analogues corresponding to regions of the gonococcal pilin sequence, were used to detect common meningococcal and gonococcal antigenic determinants that might indicate the existence of a conserved sequence beyond residue 29. Antibody to intact gonococcal pili or to the variable CNBR-3 region of gonococcal pilin detected little shared antigenicity with meningococcal pilin. However, pilin from all tested meningococcal isolates reacted with antibody to the CNBR-2 fragment of gonococcal pilin, a region highly conserved among gonococcal strains. Meningococcal pilins were also broadly crossreactive with antibody to a synthetic peptide corresponding to residues 69-84 of the gonococcal sequence, a part of the CNBR-2 region that appears to be critical for gonococcal receptor-binding function. If a sequence similar to 69-84 is also important for receptor-binding function in meningococcal pili, a peptide corresponding to this region may elicit antibodies that block the adherence function of pili elaborated by both Neisseria gonorrhoeae and N. meningitidis.

Disseminated gonococcal infection in a married couple

The rare occurrence of disseminated gonococcal infection in a married couple is reported. These cases support the concept that bacterial rather than host factors are more important in determining the disease manifestations in gonorrhoea.

Structural and antigenic analysis of meningococcal piliation

Pilin with an Mr of 16,500 was purified to homogeneity from Neisseria meningitidis SP3428. Procedures which provided useful separation during purification included high-pressure liquid chromatography with a TSK size exclusion column, Sephacryl S-200 column chromatography, ion-exchange chromatography with SP-Sephadex, and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The amino acid composition of this pilin was similar to that previously reported for this species. The sequence of N-terminal 51 amino acids was also determined. The protein lacked a modified phenylalanine at the amino terminus and displayed six residues which were different from Neisseria gonorrhoeae in that region of the molecule determined to be the lectin-binding domain. Monoclonal antibody raised to this pilin was employed, along with a monoclonal antibody to an epitope common to all gonococcal pilins, to analyze the intra- and interstrain heterogeneity of meningococcal piliation. The results indicate that N. meningitidis displays considerable intra- and interstrain heterogeneity with respect to both pilus subunit size and antigenicity. The Mr of subunits ranged from 13,000 to 20,000.

Strain-specific and common epitopes of gonococcal pili

The antigenic structure of gonococcal pilin, strain MS11 (Tr), was investigated by assaying the binding of antisera engendered by intact pili from strains MS11 and R10 and their two major cyanogen bromide-generated fragments, CNBr-2 (residues 9-92) and CNBr-2 (residues 93-159), to synthetic peptides corresponding to the amino acid sequence of MS11 pilin. Four peptides were synthesized corresponding to regions of sequence variation between MS11 and R10 gonococcal pilin. Antisera against the homologous pilus filament and against its CNBr-3 fragment bind peptides equivalent to residues 121-134 and 135-151, which comprise the 30 amino acid disulfide loop near the carboxyl terminus of the protein. Heterologous pili antisera did not bind these peptides. Absorption studies proved that each peptide contained an independent, strain-specific epitope. Synthetic peptides corresponding to regions of identical sequence between MS11 and R10 pilin were used in similar binding experiments to localize a weakly immunogenic, common determinant between residues 48 and 60. less than 15% of the antibodies raised against intact pili were directed at this site. Antisera raised against MS11 or R10 CNBr-2 bind a separate peptide, residues 69-80. This region is immunogenic only as a fragment, not in the intact pilus filament.

Gonococcal pili. Primary structure and receptor binding domain

The complete amino acid sequence of pilin from gonococcal strain MS11 and the sequence of constant and variable regions from strain R10 pilin have been determined in order to elucidate the structural basis for adherence function, antigenic diversity, and polymeric structure. The MS11 pilin sequence consists of 159 amino acids in a single polypeptide chain with two cysteines in disulfide linkage and serine-bonded phosphate residues. TC-2 (31-111), a soluble monomeric pilus peptide prepared by arginine-specific digestion, bound human endocervical, but not buccal or HeLa cells and therefore is postulated to encompass the receptor binding domain. Variable regions of CNBr-3 appear to confer antigenic diversity and comprise segments in which changes in the position of charged residues occur in hydrophilic, beta-turns. Residues 2-21 and 202-221 of gonococcal pilins and lower eucaryotic actins, respectively, exhibit 50% homology. When these residues are arranged at intervals of 100 degrees of arc on "helical wheels," the identical amino acids comprise a hydrophobic face on one side of the helix. This observation, the hydrophobic character of this region and the tendency for TC-1 (residues 1-30) to aggregate in water, suggest that this stretch interacts with other subunits to stabilize polymeric structure.

Do pili play a role in pathogenicity of Haemophilus influenzae type B?

Surface components of Haemophilus influenzae type b (Hib) responsible for mucosal adherence were identified through assay of in-vitro attachment to human buccal epithelial cells (EC). Among many Hib strains from cerebrospinal fluid, blood, or the nasopharynx (NP), two isolates from NP were found to be exceptionally adherent. Adherence correlated with agglutination of human red blood cells (RBC). The adherent strains displayed pili, not previously described for Hib or other encapsulated H. influenzae. Moreover, highly adherent, piliated subpopulations of bacteria could be selected from any strain, but were lost upon subculture. Thus, the potential to express pili may be general for Hib and may aid the NP colonisation which precedes systemic invasion by this organism. Piliation was correlated with the amount of an outer membrane protein with a molecular weight of about 20,000 daltons, which had proved to be immunogenic in an 8-month-old child.

Attachment of gonococcal pili to lectin-resistant clones of Chinese hamster ovary cells

Pili facilitate the attachment of virulent Neisseria gonorrhoeae to host cells. Isolated pili and peptides from pili obtained by cyanogen bromide cleavage were used in attachment assays to Chinese hamster ovary cells and their lectin-resistant clones. Pili and the largest cyanogen bromide fragment (CNBrI) from the amino-terminal portion of the pilin molecule attached to a greater degree to the parent cell and showed 40 to 75% reduced attachment to clones deficient in cell surface oligosaccharides. The CNBrI fragment, with a molecular weight of approximately 10,000, bound specifically to host proteins with subunit molecular weights of 14,000 to 16,000 that were electrophoretically transferred onto nitrocellulose sheets from polyacrylamide gel patterns of host cells. Periodate or galactosidase treatment of pili or the CNBrI fragment markedly reduced attachment, suggesting the importance of galactose residues on pili for their attachment function. Similarly, highly purified exoglycosidase or trypsin treatment of the parent cell reduced attachment, suggesting that oligosaccharide moieties of cell surface components (glycoproteins or glycolipids or both) were receptors for pili attachment. This study indicated that the portion of the pilin molecule involved in attachment resides on the CNBrI fragment and that sugar moieties, both on pili and on the host cell, were required for optimal attachment.

Genital antibody response to a parenteral gonococcal pilus vaccine

A parenteral gonococcal pilus vaccine which has previously been shown to be safe and antigenic also results in the production of specific local genital antibody. All three major antibody classes were present in the local secretions, but immunoglobulin A predominated, a portion of which is dimeric 11S immunoglobulin A. This mucosal antibody is also capable of blocking the attachment of gonococci to epithelial cells. The antibody cross-reacted with five heterologous pili in a solid-phase radioimmunoassay. These results are encouraging and suggest that a gonococcal pilus vaccine may be efficacious in preventing gonorrhea.

Effect of estrogens on bacterial adherence to HeLa cells

Incubating confluent cell culture HeLa cells for 18 h with increasing concentrations of estrogens progressively enhanced the subsequent attachment of a variety of radiolabeled bacteria to the HeLa cells. This effect was not caused by other hormones and was not produced by 1-h incubations of HeLa cells or bacteria with hormones. Estrogens did not similarly affect two other receptor cell lines studied. The addition of metabolic inhibitors showed that this effect of estrogens on HeLa cells was energy dependent and involved protein synthesis. Concurrent incubation of the HeLa cells and estrogens with the antiestrogen nafoxidine blocked the subsequent increase in adherence. These data suggest that estrogen receptors are present in HeLa cells and that hormonally-induced alterations in the synthesis of bacterial receptor sites may modify the capacity of certain cells to bind bacteria.

Serology of Neisseria gonorrhoeae: W-antigen serogrouping by coagglutination and protein I serotyping by enzyme-linked immunosorbent assay both detect protein I antigens

A total of 224 strains were serogrouped by coagglutination (COA) and serotyped by protein I enzyme-linked immunosorbent assay (ELISA). Of these strains, 61 were from patients with disseminated gonococcal infection, 21 were from patients with pelvic inflammatory disease, and 115 were from patients with uncomplicated gonococcal infection in Singapore, the Philippines, and Denmark. Twenty-seven were laboratory reference strains. Of the patient strains, 102 belonged to COA serogroup WI, and all of the 100 strains that typed with protein I serotypes 1, 2, or 3 were in this group. Most of the strains of gonococci from the 61 patients with disseminated gonococcal infection were within this group (COA WI, 53 or 87%; protein I serotypes 1, 2, or 3, 51 or 84%). All 46 strains that were protein I serotypes 4 through 7 were also COA serogroup WII. Protein I serotypes 8 and 9 accounted for 49 (25%) of the 197 patient strains. Twenty-eight of these strains typed as COA serogroup WII, 20 typed as serogroup WIII, and 1 typed as serogroups WII and WIII. COA W serogrouping and protein I ELISA both appeared to detect antigens on the protein I molecule of the outer membrane of Neisseria gonorrhoeae. Protein I serotyping, which uses unboiled organisms, may generally recognize more variable and surface-exposed antigenic determinants. In contrast, COA W serogrouping, which uses boiled organisms, may recognize less exposed shared antigenic determinants in addition to variable protein I antigenic determinants. Both methods may prove useful for further studies of the epidemiology and pathogenesis of gonorrhea.

Gonococcal pilus vaccine. Studies of antigenicity and inhibition of attachment

A gonococcal pilus vaccine or placebo was injected subcutaneously or intramuscularly into 71 human volunteers. The vaccine was found to be safe. The principal adverse reaction was a complaint of a sore arm, which was caused, at least in part, to the volume of material injected. 6 of 64 (9%) volunteers receiving the larger doses also complained of malaise. The vaccine was found to be antigenic. All of the volunteers developed an immunoglobulin class-specific antibody response as measured by a solid phase radioimmunoassay. The antibody was capable of blocking the attachment of gonococci to epithelial cells. A slight antibody response was also demonstrated to gonococcal lipopolysaccharide but the antibody responsible for blocking attachment of gonococci was directed entirely at the pilus protein. The stimulated antibodies were shown to crossreact with isolated pili of heterologous gonococcal strains and to block the attachment of heterologous gonococci. Absorption of immune sera by a heterologous pilus reduced the inhibition of attachment antibodies to pre-immune level, suggesting that the immune response was directed at a common pilus determinant.

Antigen-specific serotyping of Neisseria gonorrhoeae: characterization based upon principal outer membrane protein

Principal outer membrane protein (protein I) of Neisseria gonorrhoeae was prepared nearly free of lipopolysaccharide (LPS) and substantially purified from other membrane proteins by chromatography of partially purified gonococcal outer membranes over Sepharose 6B in the presence of deoxycholate at pH 9.0. This protein I of nine separate antigenic types was coated to polystyrene tubes and used in the enzyme-linked immunosorbent assay (ELISA) to measure antibody to protein I or in inhibition tests to quantitate protein I antigen. No significant inhibition of the ELISA test was produced by purified LPS from the strain used to prepare each of the protein I types or by whole gonococci bearing the same LPS but different protein I antigens as the strain used to produce a given protein I antigen. Of 125 strains of gonococci used as whole organisms to inhibit the protein I ELISA, 124 (99%) typed with one or more of the nine protein I types, and 35% of these typed with a single protein I serotype. Sixty-one of 65 (94%) strains from Seattle and Atlanta patients with disseminated gonococcal infection contained protein I serotype 1, and 16 of 24 (64%) strains from Seattle patients with salpingitis bore one or both of protein I serotypes 1 and 2.

Divergent effects of cyclic adenosine 3',5'-monophosphate on formation of type 1 fimbriae in different K-12 strains of Escherichia coli

Exogenous cyclic adenosine 3',5'-monophosphate either increased or decreased the expression of type 1 fimbriae in different cya strains of Escherichia coli, demonstrating the complexity of regulation of this surface protein.