Genetic locus for the biosynthesis of the variable portion of Neisseria gonorrhoeae lipooligosaccharide.

A locus involved in the biosynthesis of gonococcal lipooligosaccharide (LOS) has been cloned from gonococcal strain F62. The locus contains five open reading frames. The first and second reading frames are homologous, but not identical, to the fourth and fifth reading frames, respectively. Interposed is an additional reading frame which has distant homology to the Escherichia coli rfaI and rfaI genes, both glucosyl transferases involved in lipopolysaccharide core biosynthesis. The second and fifth reading frames show strong homology to the lex-1 or lic2A gene of Haemophilus influenzae, but do not contain the CAAT repeats found in this gene. Deletions of each of these five genes, of combinations of genes, and of the entire locus were constructed and introduced into parental gonococcal strain F62 by transformation. The LOS phenotypes were then analyzed by SDS-PAGE and reactivity with monoclonal antibodies. Analysis of the gonococcal mutants indicates that four of these genes are the glycosyl transferases that add GalNAc beta 1-->3Gal beta 1-->4GlcNAc beta 1-->3 Gal beta 1--4 to the substrate Glc beta 1-->4Hep--R of the inner core region. The gene with homology to E. coli rfaI/rfaI is involved with the addition of the alpha-linked galactose residue in the biosynthesis of the alternative LOS structure Gal alpha 1-->4Gal beta 1-->4Glc beta 1-->4Hep-->R. Since these genes encode LOS glycosyl transferases they have been named lgtA, lgtB, lgtC, lgtD, and lgtE. The DNA sequence analysis revealed that lgtA, lgtC, and lgtD contained poly-G tracts, which, in strain F62 were, respectively, 17, 10, and 11 bp. Thus, three of the LOS biosynthetic enzymes are potentially susceptible to premature termination by reading frame changes. It is likely that these structural features are responsible for the high-frequency genetic variation of gonococcal LOS.

Isolation of a high molecular weight polyphosphate from Neisseria gonorrhoeae.

Neisseria gonorrhoeae, as well as other Neisseriae, produce polyphosphate. This polyphosphate exists in two forms. Approximately half of it is loosely associated with the cells and can be recovered by washing in neutral buffers under conditions in which no significant lysis of the cells is observed. The other half is either intracellular or tightly associated, because it requires digestion of the cells with perchloric acid or sodium hypochlorite. Polyphosphate obtained by both methods was purified by column chromatography and chemically characterized. In contrast to other organisms, gonococci do not respond with increased polyphosphate synthesis when shifted from phosphate starvation to a phosphate-rich medium. In addition, gonococcal polyphosphate does not serve as a depletable phosphate source during phosphate starvation. All strains of Neisseriae examined produce substantial amounts of polyphosphate.

Electron microscopic studies on streptococci. II. Group A carbohydrate.

The location of Group A carbohydrate in the streptococcal cell wall has been studied by several ultrastructural techniques. The findings, based largely on use of ferritin- and horseradish peroxidase-conjugated antibodies, are interpreted as demonstrating a discrete laminar distribution of the group-specific polysaccharide. This carbohydrate layer is located on the outermost surface of the cell wall in organisms lacking protein cell wall antigens.

Purification and partial characterization of the opacity-associated proteins of Neisseria gonorrhoeae.

Gonococci, grown on agar, frequently give rise to opaque colonies. This opacity phenotype is associated with the presence of one or more outer membrane proteins of approximately 28,000 mol weight. These proteins are included within a class of proteins named proteins II. A method is described to isolate and purify the opacity-associated proteins from Neisseria gonorrhoeae. This method uses high concentrations of calcium and a zwitterionic detergent at pH 4.0. Under these conditions proteins II are readily solubilized from the outer membrane. Further purification is achieved by ion exchange and molecular sieve chromatography in the presence of the zwitterionic detergent. The opacity-associated proteins are very basic with isoelectric points varying between 9.0 to 10.0. Further evidence for their basic nature is their behavior on ion exchange chromatography and their amino acid composition.

Identification of protein antigens of group B streptococci, with special reference to the Ibc antigens.

The protein antigens of prototypes of five types of group B streptococcal strains were extracted with HCl or Triton X-100, separated by sodium dodecyl sulfate polyacrylamide electrophoresis, transferred to nitrocellulose, and examined by immunochemical staining. The Ibc proteins are shown to consist of at least two distinct protein antigens and their breakdown products. One antigen, the "beta" antigen, exists primarily as a 130,000 mol wt protein that is also able to bind human IgA. The "alpha" antigen, which has no known function, appears as a number of proteins of various molecular weights from 20,000 to 120,000. Another set of antigens, the R protein antigens of type III strains, has been identified as a group of acid-labile proteins varying in molecular weight from 100,000 to 130,000. In addition, two previously undescribed antigens have been found that are common to all five group B types.

Variation of gonococcal lipooligosaccharide structure is due to alterations in poly-G tracts in lgt genes encoding glycosyl transferases.

The lipooligosaccharide (LOS) expressed by gonococci spontaneously varies its structure at high frequency, but the underlying genetic mechanism has not been described. We have previously reported that the genes encoding the glycosyl transferases responsible for the biosynthesis of the variable alpha chain of the LOS of Neisseria gonorrhoeae are located in a locus containing five genes, lgtA, lgtB, lgtC, lgtD, and lgtE. Sequence analysis showed that lgtA, lgtC, and lgtD contained poly-G tracts within the coding frames, leading to the hypothesis that shifts in the number of guanosine residues in the poly-G tracts might be responsible for the high frequency variation in structure of gonococcal LOS. We now provide experimental evidence confirming this hypothesis.

Hemagglutination by purified type I Escherichia coli pili.

Many enterobacteria can cause agglutination of erythrocytes, but previous investigations have not proven which components of the bacteria are responsible. We used a strain of Escherichia coli K12 which causes mannose-sensitive hemagglutination (HA) of guinea pig cells. Common pili were purified from these bacteria by shearing them from the bacteria followed by selective precipitation in acid and ammonium sulfate. Isopycnic centrifugation in cesium chloride removed the remaining outer membrane protein contaminants. These pili are pure by electron microscopy and gel electrophoresis. By amino acid analysis, they have a mol wt of 17,099 and consist of 45% nonpolar residues. These purified pili agglutinate guinea pig erythrocytes, a reaction that is inhibited by anti-pili antibodies and by saccharides related in structure to D-mannose. Proteolytic treatment of erythrocytes does not diminish HA but rather increases the pili-induced HA of human cells. Neuraminidase enhances HA and mannosidase slightly diminishes it. It is concluded that purified pili alone cause HA of erythrocytes by binding to mannose-like molecules on the erythrocyte surface. Thus HA by bacterial pili serves as a useful model system for the mechanism of bacterial pili attachment ot cell membranes.

Type I Escherichia coli pili: characterization of binding to monkey kidney cells.

We have demonstrated binding of purified pili from a strain of Escherichia coli to Vero cell monolayers as a model of prokaryotic-eukaryotic cell adherence. Pili bound to the tissue culture in a rapid reaction that did not require enzymatic activation. Attachment occurred optimally at pH 4-5 and could be inhibited by analogues of D-mannose, anti-pili antibodies, or by preincubation of tissue cells with mannose-specific plant lectins. Binding remained after treatment of the monolayer with glycosidases, trypsin, or a protease mixture but was enhanced after neuraminidase treatment. These results indicate that bacterial binding can occur via pili which act like lectins and presumably bind to mannose-containing glycoproteins on mammalian cell surfaces.

Studies on gonococcus infection. I. Pili and zones of adhesion: their relation to gonococcal growth patterns.

The four colony types of several different strains of gonococci were isolated by selective transfers on agar. These colony variants differed in the degree of autoagglutination which occurred when they were grown in fluid medium. It was found that this clumping behavior was related to the colonial type, with type 2 isolates exhibiting the greatest autoagglutination followed by types 3, 1, and 4. Electron microscopic examination of thin sections indicated that the clumping in fluid medium was mediated by peculiar zones of adherence of the outer membranes of gonococci. These resembled the gap junctions seen in animal cell systems but differed in that the gonococcal membranes involved in the zone of adherence did not bear typical surface modifications. Electron microscopic study of negatively stained specimens of gonococci revealed that pili with a diameter of approximately 85 A and a length up to 4 micro were present on the surfaces of all type 1 and type 2 gonococci examined, and were not seen on any type 3 or 4 gonococci. The consistent presence of pili on type 1 and type 2 gonococci which are virulent colony forms and the lack of pili on avirulent colony types 3 and 4 suggests a relationship between the gonococcal pili and pathogenetic potential of the organisms.

Human immunity to the meningococcus. I. The role of humoral antibodies.

Susceptibility to systemic meningococcal disease is related to a selective deficiency of humoral antibodies to pathogenic strains of meningococci. In a study of the age-specific incidence of meningococcal meningitis in the United States, it was found that the proportion of individuals with serum bactericidal activity to meningococci of serogroups A, B, and C was reciprocally related to the incidence of disease. The prevalence of bactericidal activity was highest at birth and among adults, and lowest in infants between 6 and 24 months of age. Sera from 51 of 54 prospective cases of meningococcal disease among military recruits were deficient in antibodies to homologous and heterologous strains of pathogenic meningococci as determined by serum bactericidal activity and indirect immunofluorescence. Such sera, however, could support the bactericidal activity of purified human gamma globulin (Cohn fraction II), and such individuals could respond immunologically to infection with meningococci. The implication is that susceptible persons are deficient in antimeningococcal antibodies because they have not received significant exposure to meningococcal antigens in the past. The fate of individuals who lack bactericidal antibodies to pathogenic meningococci was determined during an outbreak of group C meningitis among military recruits. The incidence of disease was found to be primarily associated with the incidence of exposure of susceptibles to the pathogenic strains. Whereas 81.5% of the presumed susceptibles acquired a meningococcal strain, only 24.1% acquired an organism similar to the prevalent disease-producing strains. Of the exposed susceptibles, 38.5% developed systemic meningococcal disease.

Human immunity to the meningococcus. IV. Immunogenicity of group A and group C meningococcal polysaccharides in human volunteers.

High molecular weight group A and group C meningococcal polysaccharides had no significant toxicity for mice or guinea pigs. Furthermore, these polysaccharide preparations contained negligible amounts of biologically active endotoxin. The high molecular weight group A and group C meningococcal polysaccharides were excellent immunogens in six human volunteers. Antibodies belonging to the immunoglobulin classes IgG, IgM, and IgA were produced. These antibodies were highly meningococcocidal in the presence of complement.

Human immunity to the meningococcus. V. The effect of immunization with meningococcal group C polysaccharide on the carrier state.

Purified meningococcal polysaccharides were administered to army recruits. No adverse reactions were observed in 145 men who received group C polysaccharide, and in 53 men who were injected with group A polysaccharide. Hemagglutinating and bactericidal activity developed in the sera of all individuals with the exception of two recruits injected with A polysaccharide. During the 6 wk period of observation, the proportion of unvaccinated recruits who acquired group C meningococci in the three companies studied was 38, 42, and 69 per cent. A significantly lower proportion of the individuals vaccinated with group C polysaccharide acquired group C meningococci; 4.6, 24, and 31 per cent respectively.

Human immunity to the meningococcus. II. Development of natural immunity.

Results of the present study suggest that natural immunity to meningococcal disease is initiated, reinforced, and broadened by intermittent carriage of different strains of meningococci throughout life. In young adults, carriage of meningococci in the nasopharynx is an efficient process of immune sensitization. 92% of carriers of serogroup B, C, or Bo meningococci were found to develop increased titers of serum bactericidal activity to their own meningococcal isolate, and 87% developed bactericidal activity to heterologous strains of pathogenic meningococci. The rise in bactericidal titer occurred within 2 wk of onset of the carrier state, and was accompanied by an increase in titer of specific IgG, IgM, and IgA antibodies to meningococci. In early childhood, when few children have antibodies to pathogenic meningococci, active immunization seems to occur as a result of carriage of atypical, nonpathogenic strains. Immunity to systemic meningococcal infection among infants in the neonatal period is associated with the passive transfer of IgG antibodies from mother to fetus. The antigenic determinants which initiate the immune response to meningococci include the group-specific C polysaccharide, cross-reactive antigens, and type-specific antigens.

Electron microscopic studies on streptococci. I. M antigen.

The presence of M antigens on group A streptococci is associated with hairlike fimbriae that cover the surface of the streptococcal cell wall and are demonstrable by electron microscopy. These fimbriae also may be associated with R antigen. Like M protein, the surface fimbriae are destroyed by trypsin treatment and reappear when "trypsinized" streptococci are reincubated in fresh, trypsin-free broth. Ferritin-conjugated, type-specific antibodies localize on homologous M+ cells in a pattern suggestive of several M antigenic sites along the length of individual surface fimbria. The M-associated fimbriae remain on the residual cell wall after removal of the bulk of group-specific polysaccharide through nitrous acid extraction. This suggests attachment of the fimbriae to the mucopeptide and minor polysaccharide components remaining in the nitrous acid-extracted wall. The pattern of localization of ferritin-conjugated antibodies on homologous streptococci before and after trypsin exposure and upon reincubation of the trypsinized cells in fresh medium suggests the following hypothesis: M antigen is secreted by the cell, is partially excreted through the otherwise intact cell wall, and is bound by the wall so that M protein occupies a peripheral, exposed position on the surfaces of the streptococcal cell wall.

Studies on gonococcus infection. 3. Correlation of gonococcal colony morphology with infectivity for the chick embryo.

Comparable numbers of types 1, 2, 3, and 4 gonococci were placed on the intact chorioallantoic membrane of 236, 10-day old chick embryos. Types 1 and 2 organisms produced infection and could be cultured from chorioallantoic fluid 2 days later significantly more often (69%) than types 3 and 4 organisms (12%, P < 0.001). This confirms in an animal model the same correlation between colony types and infectivity observed in human volunteers and suggests that types 1 and 2 gonococci possess a fundamental virulence characteristic which is absent from types 3 and 4 organisms. Gonococcal infection of the chick embryo chorioallantoic cavity remains a useful model somewhat analogous to localized gonococcal infection in man.

An outer membrane protein of Neisseria meningitidis group B responsible for serotype specificity.

Meningococcal groups B and C have been subdivided into a series of serotypes based upon the antigenic specificity of protein serotype antigens (STA). The purpose of these studies was to obtain the STA by gentle methods and determine its anatomic location in the meningococcal cell. The STA was extracted from group B meningococcal strains by either 0.2 M LiCl or 0.2 M CaCl(2) and isolated from the extracts by gel filtration on Sepharose 6B or by pelleting the STA by centrifugation at 100,000 g. The isolated STA was a lipoprotein-lipopolysaccharide complex with a mol wt of approximately 4 x 10(6) daltons. Antisera prepared against the type 2 STA were bactericidal only for homologous serotype strains. The STA proved to be a constituent of the outer membrane of the cell envelope. This was shown by SDS-polyacrylamide gel electrophoresis (PAGE) of the isolated outer membrane and of the purified STA. The type 2 STA complex contains three principal proteins, one of which is predominant with a mol wt of 41,000 daltons. The type 2 STA was dissociated by Triton X-100 and separated by sucrose gradient isodensity centrifugation into two peaks. The denser peak (rho = 1.26 g/cm(3)) contained the majority of the 41,000 dalton major outer membrane protein as shown by SDS-PAGE. This peak also contained the type 2 antigenic determinant. Thus the major outer membrane protein, extracted as part of a lipoprotein-lipopolysaccharide complex, contains the type 2 STA determinant.

Intra-strain heterogeneity of gonococcal pili is related to opacity colony variance.

We have purified pili from isogenic opacity colony variants that were derived from 14 gonococcal strains. Pili purified from opaque colonies of one strain usually differed from pili purified from transparent colonies of the same strain. In 10 of the 14 strains examined, the apparent subunit molecular weight of pilin isolated from the opaque variants was larger than that seen with pilin obtained from transparent variants. In addition there were demonstrable intra-strain differences in the isoelectric point and buoyant density of pili derived from the opacity variants. Because gonococci express differing opacity phenotypes during the menstrual cycle, it is possible that the pili of these organisms may also alter in vivo.

The DNA sequence of the structural gene of gonococcal protein III and the flanking region containing a repetitive sequence. Homology of protein III with enterobacterial OmpA proteins.

The insert of a lambda gt11 clone expressing gonococcal protein III was sequenced. The deduced amino acid sequence showed a coding frame of 236 amino acids with a typical 22-amino-acid signal peptide, followed by the known NH2-terminal sequence of PIII. The mature protein has a molecular weight of 23,298. It was found that PIII had extensive and very striking homology to the carboxy-terminal portion of enterobacterial OmpA proteins. The homology encompasses the OmpA domain that is believed to be located in the periplasmic space. If the disposition of PIII across the OM is analogous, then the surface-exposed domain consists of less than 40 amino acids. These include a potential 15-amino-acid disulfide loop, a feature not found in OmpA proteins. Hybridization studies with the sequenced insert indicated that it contained a repetitive sequence that occurred at least 20 times in the genome. By additional hybridization studies the area containing the repetitive sequence was narrowed to a region of 43 bp. This region contained an exact copy of the consensus sequence of a 26-bp repetitive sequence recently described. An analogous sequence recurs in an inverted orientation 53 bp downstream.

A surface receptor specific for human IgA on group B streptococci possessing the Ibc protein antigen.

A number of group B streptococcal strains of various serotypes, Ia, Ib, Ic, II, and III were examined for their ability to bind human IgG and IgA. No strains of group B streptococci were found to bind IgG, but many strains possessing the Ibc protein antigen(s) were found to bind a significant amount of IgA. The extent of IgA binding correlated with the amount of a 130,000 mol wt, detergent-extractable protein, and reactivity with the Ic typing sera. Using nitrocellulose blots, it was found that the 130,000 mol wt protein bound human IgA. A method was developed to purify the protein while retaining its ability to bind human IgA. Using solid phase radioimmunoassays, it was determined that the protein bound to the Fc region of monomeric or polymeric IgA and that it failed to bind IgM or any IgG isotype.

The serological classification of Neisseria gonorrhoeae. I. Isolation of the outer membrane complex responsible for serotypic specificity.

Neisseria gonorrhoeae has been subdivided into several classes of serological distinct groups. The serotyping system is based upon the antigenic specificity of a protein serotype antigen. This protein is the major polypeptide of the outer membrane of the gonococcus and accounts for over 60% of that membrane's total protein. The serotype antigen complex was isolated by mild extraction of intact organisms in 200 mM lithium acetate buffer, pH 6.0 with 10 mM EDTA for 2 h at 45 degrees C. The extract was fractionated on Sepharose 6B and partially purified by precipitation at pH 4.2 by addition of 10% (vol/vol) acetic acid. Each serotype antigen has a unique subunit molecular size as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Preliminary typing of a gonococcal strain may be performed by comparative SDA-PAGE. To date, 16 different serotypes, representing a diverse distribution, have been isolated.