Effect of dilution rate on lipopolysaccharide and serum resistance of Neisseria gonorrhoeae grown in continuous culture

Modeling Neisseria meningitidis B metabolism at different specific growth rates

Neisseria meningitidis is a human pathogen that can infect diverse sites within the human host. The major diseases caused by N. meningitidis are responsible for death and disability, especially in young infants. At the Netherlands Vaccine Institute (NVI) a vaccine against serogroup B organisms is currently being developed. This study describes the influence of the growth rate of N. meningitidis on its macro-molecular composition and its metabolic activity and was determined in chemostat cultures. In the applied range of growth rates, no significant changes in RNA content and protein content with growth rate were observed in N. meningitidis. The DNA content in N. meningitidis was somewhat higher at the highest applied growth rate. The phospholipid and lipopolysaccharide content in N. meningitidis changed with growth rate but no specific trends were observed. The cellular fatty acid composition and the amino acid composition did not change significantly with growth rate. Additionally, it was found that the PorA content in outer membrane vesicles was significantly lower at the highest growth rate. The metabolic fluxes at various growth rates were calculated using flux balance analysis. Errors in fluxes were calculated using Monte Carlo Simulation and the reliability of the calculated flux distribution could be indicated, which has not been reported for this type of analysis. The yield of biomass on substrate (Y(x/s)) and the maintenance coefficient (m(s)) were determined as 0.44 (+/-0.04) g g(-1) and 0.04 (+/-0.02) g g(-1) h(-1), respectively. The growth associated energy requirement (Y(x/ATP)) and the non-growth associated ATP requirement for maintenance (m(ATP)) were estimated as 0.13 (+/-0.04) mol mol(-1) and 0.43 (+/-0.14) mol mol(-1) h(-1), respectively. It was found that the split ratio between the Entner-Doudoroff and the pentose phosphate pathway, the sole glucose utilizing pathways in N. meningitidis, had a minor effect on ATP formation rate but a major effect on the fluxes going through for instance the citric-acid cycle. For this reason, we presented flux ranges for underdetermined parts of metabolic network rather than presenting single flux values, which is more commonly done in literature.

Nontypeable Haemophilus influenzae strain 2019 produces a biofilm containing N-acetylneuraminic acid that may mimic sialylated O-linked glycans

Previous studies suggested that nontypeable Haemophilus influenzae (NTHI) can form biofilms during human and chinchilla middle ear infections. Microscopic analysis of a 5-day biofilm of NTHI strain 2019 grown in a continuous-flow chamber revealed that the biofilm had a diffuse matrix interlaced with multiple water channels. Our studies showed that biofilm production was significantly decreased when a chemically defined medium lacking N-acetylneuraminic acid (sialic acid) was used. Based on these observations, we examined mutations in seven NTHI strain 2019 genes involved in carbohydrate and lipooligosaccharide biosynthesis. NTHI strain 2019 with mutations in the genes encoding CMP-N-acetylneuraminic acid synthetase (siaB), one of the three NTHI sialyltransferases (siaA), and the undecaprenyl-phosphate alpha-N-acetylglucosaminyltransferase homolog (wecA) produced significantly smaller amounts of biofilm. NTHI strain 2019 with mutations in genes encoding phosphoglucomutase (pgm), UDP-galactose-4-epimerase, and two other NTHI sialyltransferases (lic3A and lsgB) produced biofilms that were equivalent to or larger than the biofilms produced by the parent strain. The biofilm formed by the NTHI strain 2019pgm mutant was studied with Maackia amurensis fluorescein isothiocyanate (FITC)-conjugated and Sambucus nigra tetramethyl rhodamine isocyanate (TRITC)-conjugated lectins. S. nigra TRITC-conjugated lectin bound to this biofilm, while M. amurensis FITC-conjugated lectin did not. S. nigra TRITC-conjugated lectin binding was inhibited by incubation with alpha2,6-neuraminyllactose and by pretreatment of the biofilm with Vibrio cholerae neuraminidase. Matrix-assisted laser desorption ionization-time of flight mass spectometry analysis of lipooligosaccharides isolated from a biofilm, the planktonic phase, and plate-grown organisms showed that the levels of most sialylated glycoforms were two- to fourfold greater when the lipooligosaccharide was derived from planktonic or biofilm organisms. Our data indicate that NTHI strain 2019 produces a biofilm containing alpha2,6-linked sialic acid and that the sialic acid content of the lipooligosaccharides increases concomitant with the transition of organisms to a biofilm form.

The lgtABCDE gene cluster, involved in lipooligosaccharide biosynthesis in Neisseria gonorrhoeae, contains multiple promoter sequences

Biosynthesis of the variable core domain of lipooligosaccharide (LOS) in Neisseria gonorrhoeae is mediated by glycosyl transferases encoded by lgtABCDE. Changes within homopolymeric runs within lgtA, lgtC, and lgtD affect the expression state of these genes, with the nature of the LOS expressed determined by the functionality of these genes. However, the mechanism for modulating the amount of multiple LOS chemotypes expressed in a single cell is not understood. Using mutants containing polar disruptions within the lgtABCDE locus, we determined that the expression of this locus is mediated by multiple promoters and that disruption of transcription from these promoters alters the relative levels of simultaneously expressed LOS chemotypes. Expression of the lgtABCDE locus was quantified by using xylE transcriptional fusions, and the data indicate that this locus is transcribed in trace amounts and that subtle changes in transcription result in phenotypic changes. By using rapid amplification of 5' cDNA ends, transcriptional start sites and promoter sequences were identified within lgtABCDE. Most of these promoters possessed 50 to 67% homology with the consensus gearbox promoter sequence of Escherichia coli.

Biochemical properties of Neisseria gonorrhoeae LgtE

A fragment of chromosomal DNA encoding the lgtE gene of Neisseria gonorrhoeae strain F62 was amplified by PCR and cloned into the expression vector pET15b. Functional LgtE was purified and its biochemical properties were determined. The purified enzyme was maximally active in buffer containing manganese; minimal activity was obtained in buffer containing other divalent cations. LgtE was only able to mediate the addition of UDP-galactose into neisserial lipooligosaccharides (LOSs). We used a variety of genetically defined and chemically verified LOS structures to determine acceptor specificity. LgtE was able to mediate the addition of galactose into a variety of LOS structures, indicating the this enzyme possesses broad acceptor specificity. Furthermore, it was able to add multiple galactose residues onto LOS. We also determined that this enzyme was capable of adding galactose onto both the alpha and beta chains of neisserial LOS.

Relationship between UDP-glucose 4-epimerase activity and oligoglucose glycoforms in two strains of Neisseria meningitidis

Sodium dodecyl sulfate-polyacrylamide gel analysis of lipooligosaccharide (LOS) from Neisseria meningitidis has demonstrated considerable microheterogeneity in the variable region of LOS due to the presence of novel glycoforms. As a step toward understanding the basis for the expression of these novel glycoforms, we have examined the LOS structures and UDP-glucose 4-epimerase (epimerase) activity levels in two strains (NMB and MA-1) and their respective galE mutants. Strain NMB was found to have low epimerase activity and to contain multiple glycoforms, some of which appear to contain only glucose sugars. The galE mutant had only the oligoglucose glycoforms. Strain MA-1 had higher epimerase activity at both log and stationary phases (2- and 12.5-fold, respectively) and one glycoform with a putative lactosyl structure. Strain MA-1 galE had two glycoforms that contained one or two glucose residues. To understand the molecular basis for the different epimerase activities, we examined the predicted amino acid sequences of the respective galE open reading frames and determined the relative amounts of GalE protein. We found no significant differences between the predicted amino acid sequence of the GalE protein in NMB and that in MA-1. We observed no significant differences in the level of GalE protein between MA-1 and NMB at exponential or stationary phase. We also observed an 8.2-fold drop in epimerase activity in NMB between the log and stationary phases that was not due to the GalE protein level or low glucose levels.

Genetic basis for biosynthesis, structure, and function of meningococcal lipooligosaccharide (endotoxin)

The exclusive human pathogen Neisseria meningitidis expresses lipooligosaccharide (LOS), an endotoxin that is structurally distinct from the lipopolysaccharides (LPS) of enteric Gram-negative bacilli. Differences that appear to be biologically important occur in the composition and attachment of acyl chains to lipid A, phosphorylation patterns of lipid A, and the incorporation and phosphorylation of sugar residues in the LOS inner core. Further, unlike most enteric LPS, only two to five sugar residues are attached to the meningococcal LOS inner core, and there are no multiple repeating units of O-antigens. In contrast to Escherichia coli, where the LPS biosynthesis genes are organized as large operons, the meningococcal LOS biosynthesis genes are organized into small operons or are located individually in the chromosome. Some of these genetic loci in meningococci and gonococci display polymorphisms caused by localized chromosomal rearrangements. One mechanism of antigenic variation of meningococci LOS is the regulation of glycosyltransferase activity by slipped strand mispairing of homopolymeric tracts within the 5' end of the genes encoding these enzymes, resulting in the addition of different sugar residues to the LOS molecule. Meningococcal LOS is a critical virulence factor in N. meningitidis infections and is involved in many aspects of pathogenesis, including the colonization of the human nasopharynx, survival after bloodstream invasion, and the inflammation associated with the morbidity and mortality of meningococcemia and meningitis. Meningococcal LOS, which is a component of serogroup B meningococcal vaccines currently in clinical trials, has been proposed as a candidate for a new generation of meningococcal vaccines. The rapidly expanding knowledge of the genetic basis for biosynthesis, structure, and regulation of meningococcal LOS provides insights into unique endotoxin structures and the precise role of LOS in the pathogenesis of meningococcal disease.

Regulation of gonococcal sialyltransferase, lipooligosaccharide, and serum resistance by glucose, pyruvate, and lactate

Strain F62 of Neisseria gonorrhoeae gonococci (GC) is sensitive to normal human serum unless CMP-N-acetylneuraminic acid (CMP-NANA) is present. NANA is transferred primarily to a 4.5-kDa lipooligosaccharide (LOS) structure by a GC sialyltransferase (Stase). We investigated LOS and Stase expression and serum resistance in strain F62 grown in different carbon sources and growth conditions. Pyruvate-grown GC expressed 1.9- to 5.6-fold more Stase activity than did glucose-grown GC, whereas lactate-grown GC generally expressed intermediate Stase activities. Broth-grown GC expressed two- to fourfold more Stase activity than did plate-grown GC in all carbon sources. Pyruvate- or lactate-grown GC expressed significantly more of the sialylateable 4.5-kDa LOS species than did glucose-grown GC. Anaerobically, the 4.5-kDa LOS species was expressed in greater quantity than the 4.9-kDa N-acetyl galactosamine-terminating species in all carbon sources. Pyruvate-grown GC also incorporated up to threefold more radiolabelled CMP-NANA onto the 4.5-kDa LOS species than did glucose-grown GC. In serum resistance studies, pyruvate-grown GC were 6.5- to 16.1-fold more serum resistant than glucose-grown GC at limiting CMP-NANA concentrations (1.56 to 12.50 microg/ml). Taken together, these results indicate that gonococcal expression of Stase activity is up-regulated by growth in pyruvate or lactate, which correlates with enhanced expression of the sialylateable 4.5-kDa LOS and, for growth in pyruvate, correlates with enhanced sialylation of gonococcal LOS and greater serum resistance. In different in vivo niches, gonococcal LOS sialylation, serum resistance, and interaction with host cells can be highly regulated.

The lipooligosaccharides of pathogenic gram-negative bacteria

Lipooligosaccharides (LOSs) are the major glycolipids expressed on mucosal Gram-negative bacteria, including members of the genera Neisseria, Haemophilus, Bordetella, and Branhamella. They can also be expressed on some enteric bacteria such as Campylobacter jejuni and Campylobacter coli strains. LOS is analogous to the lipopolysaccharide (LPS) found in other Gram-negative families. LOSs share similar lipid A structures with an identical array of functional activities as LPSs. LOSs lack O-antigen units with the LOS oligosaccharide structures limited to 10 saccharide units. The LOS species of pathogenic Neisseria can play a major role in pathogenesis through enhancing the resistance of the organism to killing by normal human serum. Other distinguishing characteristics of LOS are the structural and antigenic similarity of some LOS species to human glycolipids and the potential for certain LOSs to be modified in vivo by host substances or secretions. These modifications of LOS in different environments of the host result in synthesis of new LOS structures that probably benefit the survival of the pathogen. The LOS of N. gonorrhoeae can act as a ligand of human receptors, promoting invasion of host cells. It is becoming clearer that LOSs are crucial factors in the pathogenesis of bacteria that express them.

N-terminal amino acid sequences of the major outer membrane proteins from a Neisseria meningitidis group B strain isolated in Brazil

The four dominant outer membrane proteins (46, 38, 33 and 28 kDa) were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in a semi-purified preparation of vesicle membranes of a Neisseria meningitidis (N44/89, B:4:P1.15:P5.5,7) strain isolated in Brazil. The N-terminal amino acid sequence for the 46 kDa and 28 kDa proteins matched that reported by others for class 1 and 5 proteins respectively, whereas the sequence (25 amino acids) for the 38 kDa (class 3) protein was similar to class 1 meningococcal proteins. The sequence for the 33 kDa (class 4) was unique and not homologous to any known protein.

Molecular mechanisms and implications for infection of lipopolysaccharide variation in Neisseria

The lipopolysaccharides of the pathogenic Neisseria species are subject to structural variation owing to a combination of intrinsic changes in lipopolysaccharide (LPS) biosynthesis and external modification of the LPS molecule with sialic acid. This variation appears to control bacterial behaviour by altering their ability to interact with human cells and to evade host immune defences. This interconversion of LPS phenotypes, which is also observed during the natural infection, is probably due to environmental regulation of LPS biosynthesis superimposed on spontaneous changes in the DNA of distinct LPS loci. LPS variation may be a common strategy of mucosal pathogens to colonize and persist within the human host.

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.

Use of xylE fusions to demonstrate that lsi-1, a Neisseria gonorrhoeae lipooligosaccharide biosynthetic gene, and lsi-3 are not transcriptionally linked

The Neisseria gonorrhoeae lipooligosaccharide biosynthetic gene lsi-1 is preceded by a 281-bp non-protein-encoding sequence, lsi-3, that contains two pairs of inverted repeats. Gonococcal chromosomal lsi-xylE gene fusions were generated to measure the effect of the secondary structure on transcriptional attenuation. The data obtained indicate that lsi-3 and lsi-1 are not transcriptionally linked and therefore that lsi-3 is not involved in the regulation of lsi-1.

Increased sensitivity of gonococcal pilA mutants to bactericidal activity of normal human serum

PilA is a pleiotropic transcriptional regulator in Neisseria gonorrhoeae, encoded by an essential gene, pilA. It regulates pilin gene expression and stress response and it is implicated in gonococcal adaptation to external signals. All these phenomena may participate in gonococcal virulence. In this report, I tested the role of PilA in another aspect of gonococcal virulence, resistance to the bactericidal effect of normal human serum. Gonococcal mutants with impaired PilA function were more susceptible to the bactericidal effect of normal human serum than the isogenic wild-type strain. However, the major outer membrane protein and the lipooligosaccharide, targets for complement-mediated killing by the serum, were unchanged in the mutants. I discuss the role of PilA in modulating gonococcal sensitivity and resistance to normal human serum.

Anaerobic growth and cytidine 5'-monophospho-N-acetylneuraminic acid act synergistically to induce high-level serum resistance in Neisseria gonorrhoeae

In vivo, gonococci encounter a myriad of conditions not present in vitro. At some stages of infection and disease, gonococci may grow anaerobically, probably by using sodium nitrite as a terminal electron acceptor. Also, gonococci sialylate their lipooligosaccharide (LOS) in vivo, by using low concentrations of cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-NANA) present in host tissue. This sialylation is responsible for the acquired resistance of gonococci to both normal and immune human serum. Given that gonococci grown in the absence of oxygen or in the presence of CMP-NANA probably more closely resemble gonococci grown inside a human host, we studied the serum resistance of gonococci cultivated under these conditions. In the absence of CMP-NANA, anaerobically grown (anaerobic) gonococci were somewhat less sensitive to serum killing than were aerobically grown (aerobic) gonococci. However, anaerobic gonococci grown with 6 micrograms of CMP-NANA per ml exhibited almost complete serum resistance, while aerobic gonococci required 16-fold-higher CMP-NANA concentrations to achieve significant serum resistance. Anaerobic gonococci incubated in CMP-NANA converted to serum resistance two to three times faster than did similarly treated aerobic gonococci and incorporated up to six times as much sialic acid into their LOS. Gonococci can express several different LOS molecules. Anaerobic gonococci expressed the LOS molecule that acts as an acceptor for sialic acid from CMP-NANA in greater quantity than aerobic gonococci did. Finally, Triton X-100 extracts of anaerobic gonococci contained about four times more sialyltransferase activity than did extracts of aerobic gonococci. Sialyltransferase activity in these extracts was not inhibited by oxygen or enhanced by anaerobiosis. These data indicate that anaerobic conditions lead to altered LOS biosynthesis and to induction of sialyltransferase activity in gonococci. In vivo, where decreased oxygen levels and relevant concentrations of CMP-NANA are found, gonococci could readily become resistant to killing by normal and immune human serum.

Antibiotic-induced release of endotoxin in chronically bacteriuric patients

A novel in vivo model for the study of antibiotic-induced release of endotoxin from gram-negative bacteria is described. The model uses the chronically colonized urinary tracts of patients whose spinal cords have been injured. At baseline, the organisms were present in the range of 1 x 10(3) to 2 x 10(7) CFU/ml, and the concentration of endotoxin ranged from 2 x 10(-1) to 1 x 10(3) ng/ml in 44 studies. In 10 control studies, the concentration of endotoxin and the numbers of viable gram-negative bacteria over time changed by an average of less than 0.15 log10 units from the baseline values. At 2 h after antibiotic administration, the average decrease in CFU was 0.93 log10 units, and because antibiotics cause the release of endotoxin, an average increase in endotoxin concentration of 0.59 log10 units was noted in 21 studies with susceptible bacteria. Similar changes in response to antibiotic exposure were seen in studies with susceptible Pseudomonas bacteria in comparison with those seen in studies with susceptible members of the family Enterobacteriaceae. These results provide evidence that this novel model may be useful for comparing the effects of antibiotics with different modes of action, both as single agents and in combination, on the concentration of endotoxin in relation to changes in the numbers of bacteria, under conditions of bacterial replication and antibiotic exposure more closely resembling those found in vivo than is possible in other models.

Comparison of two serum bactericidal assays for Neisseria gonorrhoeae

Pooled normal human serum killing of 14 strains of Neisseria gonorrhoeae was assessed by dilution plate and microtiter methods. In both assays, the strains presented a spectrum of sensitivity to the serum. In the dilution plate assay, results with two different concentrations of human serum were similar for most, but not all of the strains tested. When data for all of the strains were compared, no correlation was found between the dilution plate and microtiter bactericidal assays. Finally, we found that the bactericidal capacities of intact and complement-depleted human sera were very similar when assessed by microtiter methods, suggesting a non-complement-mediated serum killing mechanism.

Stable expression of lipooligosaccharide antigens during attachment, internalization, and intracellular processing of Neisseria gonorrhoeae in infected epithelial cells

Immunoelectron microscopy enables the detection and localization of bacterial antigens during in vitro infection (J.F.L. Weel and J.P.M. van Putten, Microb. Pathog. 4:213-222, 1988). In this study, we have used this method to get information on the role of lipooligosaccharides (LOS) in the pathogenesis of neisserial infections at the mucosal level. Ultrathin cryosections of Chang conjunctive epithelial cells infected with Neisseria gonorrhoeae (3 to 18 h) were incubated with LOS-specific monoclonal antibodies and gold-labeled protein A and viewed in the electron microscope. Our results demonstrate that the probed LOS determinants are stably expressed during the adherence, internalization, and intracellular processing of the bacteria. There was no indication of an adaptation of the gonococcal LOS expression to the host cell environment or of a degradation of the probed epitopes. The gold particles, representing LOS molecules, were predominantly located at the bacterial membranes, but sometimes the host cell plasma membrane was labeled as well, suggesting that LOS or LOS-containing membrane fragments interacted with the eucaryotic cells. This was confirmed when purified LOS was added to the cells. Two hours after LOS exposure, gold particles were observed at the plasma membrane of a subpopulation of the cells. After 18 h of LOS exposure, gold particles were also found in large vacuoles inside the cells, suggesting that LOS molecules were internalized by the cells. The function of observed LOS binding and endocytosis in the pathogenesis of neisserial infections remains to be defined.

Energy is required for maximal adherence of Neisseria gonorrhoeae to phagocytic and nonphagocytic cells

The possibility that gonococcal energy might play a role in the interaction of Neisseria gonorrhoeae with both phagocytic and nonphagocytic cells was examined. Respiratory chain inhibitors including KCN and amobarbital resulted in reduction in gonococcal association with human neutrophils. Similar results were seen with HeLa cells and the human promyelocytic (HL-60) cell line. Identical conditions did not affect the opsonin-dependent association of Staphylococcus aureus with the same cell types. New protein synthesis by gonococci did not account for the observed reduction in association. These results suggest that energy is needed for maximal opsonin-independent association of gonococci with mammalian cells.

Role of the cell envelope in bacterial adaptation to growth in vivo in infections

To establish an infection, a pathogenic bacterium must adapt to growth in the hostile environment encountered in vivo in host tissues. The cell envelope plays a crucial role in this adaptive process, since it is involved in promoting adhesion to and colonisation of host tissues, in the acquisition of essential nutrients and in conferring resistance to host defences and to antibiotics. Its properties are ultimately determined by the information stored within the genome, which also contains the potential to respond to environmental change. The macromolecular structure and function of the cell envelope are largely determined by the growth environment and, in particular, specific nutrient limitation, growth rate, growth temperature and replication in suspension or within a surface-associated biofilm. Bacteria growing in vivo will manufacture envelopes characteristic of that environment and which will differ markedly in physiology, biochemistry and immunogenicity from those of cells grown in a standard laboratory medium. In vivo, the ability to withhold iron is an important component of the host's defence and iron deprivation has a pronounced effect on the metabolism and cell envelope properties of pathogenic bacteria. The phenotypic plasticity of the bacterial cell surface plays an important role in determining susceptibility to host defences and antibiotics and has important implications for the design and evaluation of new therapeutic strategies for the treatment and prevention of bacterial infections.

Instability of expression of lipooligosaccharides and their epitopes in Neisseria gonorrhoeae

We assessed variation in the expression of lipooligosaccharide (LOS) components and their epitopes within populations of a strain of Neisseria gonorrhoeae by using the monoclonal antibodies (MAbs) O6B4 and 3F11 and immunoenzymatic, immuno-colloidal gold electron microscopic, and sodium dodecyl sulfate-polyacrylamide gel electrophoretic procedures. Wild-type organisms varied in binding of both MAbs. We used the intensity of immunoenzymatic colony blot color to distinguish four binding variants for each MAb: red (R), pink (P), and colorless (nonreactive [N]) and an N back to R (N-R) revertant. R to P to R and R to N to R variation occurred at frequencies of 0.2% and 0.02%, respectively. The electrophoretic LOS profiles and MAb immunoblot patterns of the R, P, and N-R variants were the same as those of the wild type. LOSs of the N variants, in contrast, were of lower Mr, bound neither 3F11 nor O6B4 MAb, and contained as their major component the 3.6-kilodalton LOS that bears the L8LOS epitope of N. meningitidis. Results of immunoelectron microscopic studies were consistent with LOS binding patterns. Large number of colloidal gold particles were deposited about both R and P variants, distally from R organisms, but proximally from P organisms. N variant organisms, like their LOS, bound neither of the MAbs. N-R variant organisms were like the wild type in that they showed much variation in the amounts of MAb they bound.

Electrophoretic heterogeneity of lipopolysaccharides of Actinobacillus actinomycetemcomitans

Electrophoretic banding patterns of lipopolysaccharides (LPS), as observed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), have proved to be useful in studies relating LPS structure to virulence and as epidemiological markers. In this report, LPS of actinobacillus actinomycetemcomitans from outer membrane fractions and hot phenol-water extracts were analyzed by SDS-PAGE and LPS-specific silver-staining techniques. Both intra- and inter-strain heterogeneity of A. actinomycetemcomitans LPS was observed. Twelve strains of A. actinomycetemcomitans, representative of the three described serotypes, were assigned to LPS subtypes based on the relative mobility of their most rapidly migrating LPS band. All three serotype a strains (29523, aB75, and GA3), two (29524 and SAC11A) of five serotype b strains, and two (aB67 and SAC5A) of four serotype c strains were assigned to LPS subtype I. The three remaining serotype b strains (29522, Y4, and JP2) were assigned to LPS subtype II, and the remaining two serotype c strains (SAC6A and SAC12A) were assigned to LPS subtype III. LPS subtyping may serve as an adjunct or alternative to serotyping in epidemiological studies.

Reversible phase variation of expression of Neisseria meningitidis class 5 outer membrane proteins and their relationship to gonococcal proteins II

Neisseria meningitidis class 5 proteins are major outer membrane proteins that share many properties with the proteins II (P.II) of Neisseria gonorrhoeae. We generated two bactericidal monoclonal antibodies, each of which bound specifically to one of the two identified class 5 proteins produced by N. meningitidis FAM18. The monoclonal antibodies also bound to class 5 proteins of a limited number of other meningococcal strains. Using the bactericidal activity of the monoclonal antibodies, we demonstrated that expression of both class 5 proteins was subject to reversible phase variation in vitro. The N-terminal amino acid sequence of a purified class 5 protein revealed striking similarity to the N-terminal amino acid sequence of gonococcal P.II proteins. Using a cloned class 5 gene, we identified three potential class 5 gene loci in N. meningitidis FAM18. These class 5 sequences also had homology with gonococcal P.II gene sequences and contained the CTCTT repeat sequence believed to be important in the regulation of gonococcal P.II expression.

Comparison of meningococcal outer membrane protein vaccines solubilized with detergent or C polysaccharide

Outer membrane proteins (OMPs) were isolated from meningococcal strain H44/76 (B:15:P1.16) by detergent extraction of bacteria. A final product containing class 1 (P1.16), 3(15), 4 OMPs and 5% (w/w) lipooligosaccharide was obtained. Two experimental vaccines were prepared: OMP-detergent and OMP-C polysaccharide. The OMP-detergent vaccine tended to show a better bactericidal: ELISA ratio for the antibodies induced as compared to the OMP-C polysaccharide vaccine. The vaccine induced bactericidal antibodies appeared for the greater part to be directed against the class 1 OMP (P1.16). By comparison of cultures grown in Mueller Hinton Broth with and without 0.25% (w/v) glucose, it was found that monoclonal antibodies against the serotype OMP (class 2 or 3) were not bactericidal against meningococci grown in MHB without glucose. Antibodies against class 1 OMP and lipooligosaccharide were not influenced by this. A new major outer membrane protein (appr. 40 kd) is described that may function as a cation-specific porin.

Localization of a conserved epitope and an azurin-like domain in the H.8 protein of pathogenic Neisseria

The pathogenic neisseriae, Neisseria gonorrhoeae and Neisseria meningitidis, possess an outer membrane protein, H.8, which contains a conserved monoclonal antibody (MAb)-binding epitope in all strains tested. We have cloned and sequenced a meningococcal H.8 gene, and determined the characteristics of the predicted protein. The predicted signal peptide has features characteristic of a prokaryotic lipoprotein. The region at the N-terminal end of the mature protein (39 amino acids) is primarily composed of alanine, glutamate and proline residues arranged in imperfect repeats with the consensus sequence AAEAP. The epitope for H.8 MAb-binding was localized to a 20-amino-acid sequence within this region. The remainder of the predicted amino acid sequence shows extensive homology to azurins, which are small blue copper-binding proteins found in a limited number of species of pathogenic bacteria.

Phenotypic variation in epitope expression of the Neisseria gonorrhoeae lipooligosaccharide

Gonococcal lipooligosaccharides (LOSs) are a series of antigenically complex heteropolymers. To investigate whether all members of clonally selected populations of Neisseria gonorrhoeae express antigenically similar LOS, we studied gonococcal strains 4505 and 220 with monoclonal antibodies 6B4 and 3F11 which have specificity for different oligosaccharide epitopes on the same or comigrating LOS unit(s) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Fluorescent-antibody and immunoelectron microscopy studies indicated that all members of the clonally selected populations were not homogenous for the epitopes these antibodies recognized. Fluorescence-activated cell sorting studies of 3F11-coated strain 220 indicated that the density of epitope expression was a function of time of growth. The population could be separated into two broad groups corresponding to organisms staining strongly or weakly for the 3F11 epitope, and the epitope density decreased during the late-log and stationary phases of growth. Sequentially staining organisms on Formvar grids with 6B4 and 3F11, followed by staining with either 5- or 15-nm colloidal gold spheres conjugated to goat anti-mouse immunoglobulin M demonstrated the following populations of cells among organisms derived from a single clone: organisms which stained for both 6B4 and 3F11 epitopes and organisms which stained for either 6B4 epitopes alone or 3F11 epitopes alone. Immunofluorescence microscopy studies with rhodamine and fluorescein goat anti-mouse immunoglobulin M conjugates sequentially staining organisms on Formvar grids with 3F11 and 6B4 also demonstrated these three populations. Analysis of LOS preparations made over the last 5 years indicated no change in serotype antigen concentration or in sodium dodecyl sulfate-polyacrylamide gel electrophoresis migration pattern. These studies indicate that while clonally selected strains of Neisseria gonorrhoeae undergo phenotypic variation at the epitope level, the impact of this variation on the total LOS of the population has little overall effect on its antigenic or physicochemical properties.

Stability of expression of Neisseria gonorrhoeae lipooligosaccharides

We compared multiple lipooligosaccharide (LOS) extracts from individual strains of Neisseria gonorrhoeae. Each of the extracts was prepared from single mass cultures grown on solid media under similar conditions but separated by time. We found only subtle variations in the number, electrophoretic mobility, and concentration of components of the LOSs from individual strains. We found no variation in the expression of a 3.6-kilodalton LOS component that carries the L8 LOS epitope. A significant variation in the 3-deoxy-D-manno-octulosonic acid content was found among different extracts from the same strain, but this variation appeared to be unrelated to the other LOS characteristics studied.

Antigenic and physical diversity of Neisseria gonorrhoeae lipooligosaccharides

We used mouse monoclonal antibodies (MAbs) to characterize Neisseria gonorrhoeae lipooligosaccharide (LOS). LOSs that bound two or more MAbs in a solid-phase radioimmunoassay usually bound them to different LOS components, as separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE); strains with multiple LOS components on SDS-PAGE usually bound more than one MAb. However, the LOS of some strains bound the same MAb to two LOS components with different relative molecular weights, and some individual LOS components bound more than one MAb. LOSs from different strains bound different amounts of the same MAb at saturation, reflecting differences in the quantitative expression of individual LOS components. Not all components recognized by MAbs were stained by silver after periodate oxidation. Treatment with NaOH variously affected epitopes defined by different MAbs. MAb 3F11 completely inhibited and MAb 2-1-L8 partially inhibited the binding of 125I-labeled 06B4 MAb to WR220 LOS and WR220 outer membranes in competitive binding studies. Other MAbs did not compete with the binding of 125I-labeled 06B4 to either antigen. We conclude that a strain of N. gonorrhoeae elaborates multiple LOSs that can be separated by SDS-PAGE and that are antigenically distinct. Epitope expression within these glycolipids is complex.

Distribution of an antigenically related iron-regulated protein among the Neisseria spp

Several iron-regulated proteins of Neisseria gonorrhoeae have been reported. One of these, a 37,000-molecular-weight protein (37K protein), appears to be common to all gonococcal isolates. Recently, the occurrence of a similar protein has also been noted in N. meningitidis. The gonococcal 37K protein has been purified and used to produce both rabbit monospecific antiserum and murine monoclonal antibodies. Using these antibody reagents, we analyzed 57 strains from nine species of Neisseria and the closely related organism Branhamella catarrhalis for the presence of proteins antigenically related to the gonococcal 37K protein. Strains grown on medium with low iron content were probed for antigenic reactivity by Western blot techniques and an enzyme-linked immunosorbent assay. Proteins which cross-reacted with the rabbit monospecific antiserum were designated as AgR-37K proteins. The data indicated that the AgR-37K proteins were conserved among the 40 strains of N. gonorrhoeae, N. meningitidis, N. lactamica, and N. cinerea tested. Seventeen strains from other species of Neisseria and Branhamella did not express AgR-37K proteins with the exception of one N. subflava isolate. All AgR-37K proteins appeared to be regulated by the amount of available iron in the growth medium. Murine monoclonal antibodies were used to probe the antigenic heterogeneity of the AgR-37K proteins from different Neisseria spp. Two of seven monoclonal antibodies were broadly cross-reactive, recognizing the AgR-37K proteins from all species examined. The remaining five monoclonal antibodies were more discriminating, recognizing the AgR-37K proteins from certain species. The antigenic conservation of these AgR-37K proteins, particularly among the pathogenic members of the genus Neisseria, may imply that these proteins serve a common function in pathogenicity.

Influence of nutrient limitation and low pH on serogroup B Neisseria meningitidis capsular polysaccharide levels: correlation with virulence for mice

Neisseria meningitidis strain M986, which possesses a polyanionic sialic acid capsular polysaccharide, was resistant to the bactericidal effects of normal rabbit serum, but sensitive when immune serum and complement were present. An isogenic strain PRM102, deficient in the ability to produce capsular polysaccharide, was sensitive to normal serum. Strain M986, when grown under conditions of low pH or nutrient limitation, synthesized increased levels of capsular polysaccharide. This was accompanied by an increase in cell surface hydrophilicity and virulence for mice. Cells grown in low-pH, iron-limited medium synthesized the highest concentration of polysaccharide and exhibited the highest cell surface hydrophilicity and virulence among the cases examined. The increase in capsular polysaccharide was partly explained by a decrease in the specific activity of a membrane-bound cytidine monophosphate-N acetylneuraminic acid hydrolase. The results suggest that conditions of nutrient limitation and low pH exert profound effects on the physicochemical nature of the meningococcal cell surface which, in turn, cumulate in enhanced virulence of this organism for mice.

Affinity chromatography for purification of antibodies to Neisseria gonorrhoeae and Neisseria meningitidis lipopolysaccharides

Lipopolysaccharides (LPSs) were prepared by phenol-water extraction of the gonococcal strain 8551 and the group B meningococcal strain 44/76, digested with pronase, and purified by ultracentrifugation and Sepharose CL-6B fractionation in the presence of 1.5 per cent sodium deoxycholate. On SDS-PAGE with 10 per cent acrylamide the purified 125I-labelled LPSs migrated as single, low-molecular-weight components. The LPSs were coupled to CNBr-activated Sepharose 4B for affinity purification of antibodies to the common antigenic factor 1 and the sero-type factor 5 of LPS 8551, and antibodies to LPS 44/76. The antibodies eluted showed ELISA activity against wells coated with LPS or whole cells of the bacteria, the antibody activity being inhibited by LPS. SDS-PAGE of whole cells of the strain 8551 and immunoblotting with the anti-factor 1 or -factor 5 antibodies resulted in single, broad bands corresponding to the low-molecular-weight LPS subunits.