Immunoelectron microscopic localization of outer membrane proteins II on the surface of Neisseria gonorrhoeae

Infection of synovial fibroblasts in culture by Yersinia enterocolitica and Salmonella enterica serovar Enteritidis: ultrastructural investigation with respect to the pathogenesis of reactive arthritis

Synovial fibroblasts were infected with Yersinia enterocolitica or Salmonella enterica serovar Enteritidis and analyzed by electron microscopy and fluorescence in situ hybridization. Intracellular bacterial replication was followed by degradation leading to "ghosts" possessing lipopolysaccharides but not DNA. However, single bacteria survived for more than 2 weeks. Therefore, transient intra-articular infection might be the missing link between initial intestinal infection and late synovial inflammation in the pathogenesis of reactive arthritis.

Neisseria gonorrhoeae MS11mkC opacity protein expression in vitro and during human volunteer infectivity studies

BACKGROUND AND OBJECTIVES

Neisseria gonorrhoeae MS11mkC harbors 11 independently expressed opacity (Opa) protein genes with distinct in vitro expression frequencies. In experimental infections in which human male volunteers were inoculated with transparent (Opa), piliated (P+) strains, the authors associate onset of symptoms with recovery of opaque (Opa+) gonococci.

GOALS

In vitro and recovered (Opa) protein expression rates were compared to determine if the human host influences Opa expression.

STUDY DESIGN

Opa expression was determined using Western immunoblot analysis; Opa sizes were determined using a scanning densitometer.

RESULTS

Seven of 10 Opa proteins were identified in gonococci recovered from all of the volunteers at frequencies consistent with in vitro results (Opa C, 29.5 kDa; Opa K, 30 kDa; Opa G, 31 kDa; Opa I, 32 kDa; Opa J, 33 kDa; Opa D, 34 kDa; and Opa H, 37 kDa) (P > or = 0.01, Fisher exact test). Opa B (30.5 kDa) was identified at lower than expected frequencies, whereas Opa E (31.2) and F (31.5) were identified at higher' than expected frequencies. When recovered gonococci were reanalyzed for in vitro expression frequencies, they were consistent with preinfection frequencies.

CONCLUSIONS

The host may influence the prevalence of some Opa proteins.

Sequence diversity, predicted two-dimensional protein structure, and epitope mapping of neisserial Opa proteins

The sequence diversity of 45 Opa outer membrane proteins from Neisseria meningitidis, Neisseria gonorrhoeae, Neisseria sicca, and Neisseria flava indicates that horizontal genetic exchange of opa alleles has been rare between these species. A two-dimensional structural model containing four surface-exposed loops was constructed based on rules derived from porin crystal structure and on conservation of sequence homology within transmembrane beta-strands. The minimal continuous epitopes recognized by 23 monoclonal antibodies were mapped to loops 2 and 3. Some of these epitopes are localized on the bacterial cell surface, in support of the model.

Recombinational reassortment among opa genes from ET-37 complex Neisseria meningitidis isolates of diverse geographical origins

Opacity (Opa) proteins are a family of antigenically variable outer-membrane proteins of Neisseria meningitidis. ET-37 complex meningococci, defined by multilocus enzyme electrophoresis, have been isolated on different continents. Twenty-six different Opa proteins have been observed within strains of the ET-37 complex isolated between the 1960s and the 1980s, although individual strains have only four opa genes per chromosome. In this work the opa genes of four closely related ET-37 complex N. meningitidis strains recently isolated from Mali, West Africa were characterized and compared with the opa genes of strain FAM18, an ET-37 complex isolate from the USA. DNA sequence analysis and Southern blot experiments indicated that recombinational reassortment, including gene duplication and import by horizontal genetic exchange, has occurred in the opa genes within the ET-37 complex, resulting in two partially different Opa repertoires being present in FAM18 and the Mali isolates. Using synthetic peptides derived from the hypervariable (HV) regions of opa genes, the epitopes for nine mAbs were mapped. These bacteria, isolated on different continents, contain both shared and unique opa HV regions encoding epitopes recognized by mAbs and show evidence of recombinational reassortment of the HV regions.

Microevolution within a clonal population of pathogenic bacteria: recombination, gene duplication and horizontal genetic exchange in the opa gene family of Neisseria meningitidis

Opacity (Opa) proteins are a family of antigenically variable outer-membrane proteins of Neisseria meningitidis. Even among clonally related epidemic meningococcal isolates, there is greater variation of Opa protein expression than can be accounted for by the opa gene repertoire of any individual strain. We characterized the opa genes of eight closely related isolates of serogroup A N. meningitidis (subgroup IV-1) from a recent meningitis epidemic in West Africa. DNA sequence analysis and Southern blot experiments indicated that changes occurred in the opa genes of these bacteria as they spread through the human population, over a relatively short period of time. Such changes in one or a few loci within a clonal population are referred to as microevolution. The distribution of sequences present in hypervariable (HV) regions of the opa genes suggests that duplication of all or part of opa genes into other opa loci changed the repertoire of Opa proteins that could be expressed. Additional variability in this gene family appears to have been introduced by horizontal exchange of opa sequences from other meningococcal strains and from Neisseria gonorrhoeae. These results indicate that processes of recombination and genetic exchange contributed to variability in major surface antigens of this clonal population of pathogenic bacteria.

Multiple gonococcal opacity proteins are expressed during experimental urethral infection in the male

The opacity (Opa) proteins of Neisseria gonorrhoeae are a family of outer membrane proteins demonstrating phase and antigenic variation. N. gonorrhoeae strain FA0190 has 11 opa loci that encode at least 8 antigenically distinct Opa proteins. To determine if expression of one Opa protein or a subset of them is favored during gonococcal infection, we inoculated Opa-negative variants of strain FA1090 intraurethrally into male volunteers. The Opa phenotype of gonococci isolated from urine and urethral swab cultures from nine infected subjects was determined. Opa proteins were expressed in a large proportion of the reisolates from the infected subjects. Gonococci cultured from urine or urethral swab samples from six of the subjects were uniformly Opa positive, with the predominant Opa variants differing among subjects. Three different Opa proteins were represented as the predominant type in at least one subject each. In three subjects, there was more heterogeneity in Opa phenotype of the reisolates, including the presence of Opa-negative variants. An increase in the proportion of isolates expressing multiple Opa proteins occurred over time in most subjects. Passage of the inoculum in vitro did not result in similar changes in Opa expression. There was no detectable difference in infectivity of an Opa-negative variant and one expressing an Opa protein (OpaF) that was highly represented in reisolates from the original nine subjects. Reisolates from three infected volunteers inoculated with the OpaF variant showed continued expression of OpaF alone or in conjunction with other Opa proteins. These results demonstrate that there is strong selection for expression of one or more Opa proteins by strain FA1090 in vivo, but that no single protein is preferentially expressed during early infection in the male urethra.

Characterization of naturally elaborated blebs from serum-susceptible and serum-resistant strains of Neisseria gonorrhoeae

Outer-membrane blebs from two serum-susceptible and two serum-resistant strains of Neisseria gonorrhoeae were characterized. In general, bleb surfaces resembled cell surfaces, but there were qualitative and quantitative protein differences in blebs released by serum-susceptible and serum-resistant strains. Relative to blebs from serum-resistant strains, blebs from serum-susceptible strains expressed reduced amounts of major outer-membrane proteins I and III, and little if any 68,000 Dalton outer-membrane protein.

Prevalence of gene sequences coding for hypervariable regions of Opa (protein II) in Neisseria gonorrhoeae

Opas (protein IIs) are a family of surface-exposed proteins of Neisseria gonorrhoeae. Each strain of N. gonorrhoeae has multiple (10-11) genes encoding for Opas. Identifiable elements in opa genes include the coding repeat within the signal sequence, conserve 5' and 3' regions, and hypervariable regions (HV1 and HV2) located within the structural gene. N. gonorrhoeae strains appear to have many biological properties in common that are either HV-region-mediated or associated with the presence of specific HV regions, suggesting that HV regions could be found in many clinical isolates. Oligonucleotides from three source strains representing three conserved regions of opa, 12 HV1 regions, and 14 HV2 regions were used by dot blot analysis to probe 120 clinical isolates of N. gonorrhoeae. The probe for the coding repeat hybridized to all 120 strains, the 3' conserved-region probe reacted with 98% of the strains, and the 5' conserved-region probe with 90% of the strains. Nine HV1 probes hybridized to 3.3-39.2% of the strains, and 13 of the HV2 probes hybridized to 1.7-25% of the isolates. Analysis of the number of probes that hybridized to each of the isolates showed that 19% did not hybridize with any of the HV1 probes and 25% did not hybridize with any of the HV2 probes. Approximately three-quarters of the isolates hybridized with one, two or three of the HV1 probes or one, two or three of the HV2 probes; 89% of the isolates hybridized to least one HV1 or one HV2 probe. The data indicate that some genes encoding HV regions of N. gonorrhoeae Opa proteins are widely distributed in nature.

In situ expression and localization of Neisseria gonorrhoeae opacity proteins in infected epithelial cells: apparent role of Opa proteins in cellular invasion

During natural infection, gonococcal opacity proteins (Opa) undergo rapid phase variation, but how this phenomenon contributes to the virulence of the bacteria is not well understood. In the present immunomorphological study we examined the actual Opa status of individual gonococci during various stages of gonococcal infection of Chang epithelial cells, by probing ultrathin sections of infected specimens with Opa-specific monoclonal antibodies. Our results demonstrate a heterogeneous Opa expression during the initial interaction of the bacteria, but an almost 100% expression of one of the probed Opas during their secondary attachment and entry into the host cells, suggesting a role for distinct Opas in cellular penetration. The association between Opa expression, tight attachment, and bacterial invasion into the host cells could be confirmed with isogenic variants that expressed different Opa proteins. Once inside the epithelial cells, both morphologically intact, Opa positive and morphologically disintegrated, Opa negative bacteria were observed. The loss of Opa immunoreactivity in intracellular gonococci could not be related to the presence of a particular Opa protein, but could be mimicked by incubating the organisms with extracts of sonicated uninfected epithelial cells, suggesting that it was caused by host cell proteolytic activity. Taken together, our data suggest that Opa phase transitions confer a functional adaptation of the bacteria enabling host cell penetration.

Binding of colloidal gold-labeled salivary proline-rich proteins to Actinomyces viscosus type 1 fimbriae

Salivary proline-rich proteins (PRPs), which were purified from parotid saliva, were adsorbed onto 15-nm-diameter gold particles to visualize specific binding of the salivary molecules to Actinomyces viscosus type 1 fimbriae. Negatively stained preparations incubated with PRP-gold conjugates but not bovine serum albumin-gold complexes bound specifically to bacteria possessing type 1 fimbriae, A. viscosus T14V-J1 and 5519. Binding of the PRP-gold probes to strains deficient in type 1 fimbriae, i.e., strains 5951 (type 2 fimbriae only) and 147 (no fimbriae), was negligible.

Monoclonal antibodies to outer membrane protein PII block interactions of Neisseria gonorrhoeae with human neutrophils

Nonopsonic binding of gonococci to human neutrophils appears to be mediated by a family of heat-modifiable outer membrane proteins termed protein IIs (PIIs). We studied the ability of a wide variety of antigonococcal monoclonal antibodies (MAbs) to inhibit the interactions of nonpiliated PII+ gonococci with human neutrophils by measuring gonococcal adherence to neutrophils and subsequent luminol-enhanced neutrophil chemiluminescence. From one set of 95 MAbs reacting with whole gonococci, only two, 7VA2 and 7B9, inhibited the ability of gonococci to induce neutrophil chemiluminescence. 7VA2 and 7B9 both reacted only with PII. MAb 53C4, from a smaller set of anti-PII MAbs, inhibited adherence to neutrophils of PII variants that bound 53C4, but not of PII variants that did not. It also inhibited gonococcus-induced neutrophil chemiluminescence. Using a whole-cell binding assay and Western blotting (immunoblotting), we showed that MAb 53C4 bound to one PII (PII4) of strain F62 and to two PIIs (PIIb and PIId) of strain FA1090. The present studies confirm and extend the role of PII in gonococcal adherence to and stimulation of human neutrophils and show intrastrain conservation of PII epitopes. The results indicate that PII is the only outer membrane component involved in adherence of nonpiliated gonococci to human neutrophils.

Characterization of the repertoire of hypervariable regions in the Protein II (opa) gene family of Neisseria gonorrhoeae

P.II outer membrane proteins of Neisseria gonorrhoeae are encoded by a family of closely related genes. Although the genes are highly conserved, major differences in sequence among them occur in two short regions, designated hypervariable regions 1 (HV1) and 2 (HV2). In this study, we determined the number and DNA sequence of the hypervariable regions in the P.II genes of strains FA1090. The FA1090 chromosome contained at least eleven P.II loci, having six different versions each of HV1 and HV2 among them. Southern blotting with HV-specific oligonucleotides showed that each version was present in one to three copies, and that there were nine unique combinations of HV1 and HV2 in the P.II genes. Although each of the versions of HV1 or HV2 had a unique DNA sequence, there were some similarities among them, particularly when certain ones were compared. Restriction fragments containing only the HV regions were cloned into an expression vector to demonstrate that the epitopes recognized by a set of monoclonal antibodies specific for different FA1090 P.II proteins were completely encoded by either HV1 or HV2.

Immunoelectron microscopy of lipopolysaccharide in Chlamydia trachomatis

Monoclonal antibodies (MAb) specific for Chlamydia trachomatis lipopolysaccharide (LPS) and major outer membrane protein (MOMP) were used for immunoelectron microscopy analysis. MAb specific for MOMP showed strong reaction with the chlamydial surface, whereas MAb specific for LPS showed strong association of gold particles with the periphery of the chlamydial body. After fixation of the chlamydia cells, the reactivity was, however, similar to the anti-MOMP reactivity. Enzyme-linked immunosorbent assay showed that MAb specific for LPS could remove LPS from the chlamydial membrane.

Expression and phase variation of gonococcal P.II genes in Escherichia coli involves ribosomal frameshifting and slipped-strand mispairing

Expression and phase variation of Neisseria gonorrhoeae P.II genes in Escherichia coli were studied using TnphoA fusions. Fusions were created in the P.IIc gene of N. gonorrhoeae JS3 using lambda TnphoA-1 and were characterized by restriction digestion and dideoxy sequencing. Three fusions were chosen for further study; Tnp7 (fusion junction at mature amino acid 7), Tnp57 (amino acid 57), Tnp66 (amino acid 66). All fusions were in frame with the P.IIc coding sequence but were out of frame with the purported initiation codon. All fusion constructions were shown to phase vary in E. coli in an analogous fashion to that seen in N. gonorrhoeae, i.e. phase changes (in a recA background) at a frequency of c. 10(-3) accompanied by an alteration at the DNA level of the number of coding repeats (CRs). In vitro mutagenesis of the fusion constructions indicated that expression of out of frame P.II genes in E. coli was probably the result of ribosomal frameshifting within the run of 'A' residues immediately preceding the CR region and not due to low-level false initiation at codons other than the ATG initiation codon (as had previously been suggested). The mechanism for P.IIc::phoA phase variation appears to be related to the 'slipped-strand mispairing' mechanism responsible for frameshift mutations in a number of other bacterial genes containing short, direct, tandem repeats.

Phase variation of gonococcal protein II: regulation of gene expression by slipped-strand mispairing of a repetitive DNA sequence

Expression of outer membrane protein II (P.II) of Neisseria gonorrhoeae is subject to reversible phase variation at a rate of 10(-3)-10(-4)/cell/generation. The signal peptide coding regions of P.II genes contain variable numbers of tandem repeats of the sequence CTCTT. Changes in the number of CTCTT units, leading to frameshifting within the gene, are responsible for changes in P.II expression. Phase variation mediated by the CTCTT repeat also occurred in E. coli, as assayed with a P.II-alkaline phosphatase (phoA) gene fusion. Phase variation in both the gonococcus and E. coli was recA-independent, occurred at similar rates, and involved insertions or deletions of one or more repeat units. The characteristics of the phase variation process were consistent with a model in which expression of P.II genes is regulated by slipped-strand mispairing of the DNA in the CTCTT repeat region.

Accessibility of gonococcal and meningococcal surface antigens: immunogold labeling for quantitative electron microscopy

The parallel application of two electron microscopic immunogold labeling procedures was used to assess the surface exposure and accessibility of gonococcal and meningococcal surface antigens. Monoclonal antibodies were used as markers for the surface antigens, i.e., outer membrane proteins and lipooligosaccharides. To evaluate the labeling densities obtained after incubation of whole bacteria in suspension or ultrathin cryosections of bacteria, a method of electron microscopic quantitation was developed. Incubation of whole bacterial suspensions with monoclonal antibodies and protein A-gold resulted in specific labeling of the bacterial surfaces. However, the labeling densities varied largely in each cell. By contrast, cryosections showed uniform heavy labeling densities at the surface of the outer membranes of all cells. Apparently, by sectioning the cells the antigen-masking barrier could be evaded, and steric hindrance was no longer restrictive. Thus, a better estimate of both the presence and the surface exposure, i.e., the accessibility of antigens, could be made. Such information is essential for us to better understand host-bacterial interactions and to develop new vaccines.

Expression of outer membrane protein II by gonococci in experimental gonorrhea

Gonorrheal urethritis was induced in three males by intraurethral instillation of predominantly pilus+ protein II- gonococci. Virtually all gonococci reisolated from the infected men exhibited protein II+ phenotype. The reisolated gonococci expressed five distinct outer membrane protein II species. Protein IIc+ organisms predominated in urines of all three subjects, but variants expressing this particular protein II were rarely spawned in vitro by input organisms. Protein IIc+ gonococci appeared early in one man's infection; they were joined later by variants that displayed eight other protein II phenotypes, including protein II-. These results show that input protein II- gonococci are supplanted by protein IIc+ variants during incipient gonorrheal urethritis. As infection progresses, a broader variety of protein II+ variants appears.