Demonstration of a capsule on Neisseria gonorrhoeae

Functional characterization of the gonococcal polyphosphate pseudo-capsule

Neisseria gonorrhoeae is an exclusively human pathogen able to evade the host immune system through multiple mechanisms. Gonococci accumulate a large portion of phosphate moieties as polyphosphate (polyP) on the exterior of the cell. Although its polyanionic nature has suggested that it may form a protective shield on the cell surface, its role remains controversial. Taking advantage of a recombinant His-tagged polyP-binding protein, the presence of a polyP pseudo-capsule in gonococcus was demonstrated. Interestingly, the polyP pseudo-capsule was found to be present in specific strains only. To investigate its putative role in host immune evasion mechanisms, such as resistance to serum bactericidal activity, antimicrobial peptides and phagocytosis, the enzymes involved in polyP metabolism were genetically deleted, generating mutants with altered polyP external content. The mutants with lower polyP content on their surface compared to the wild-type strains, became sensitive to complement-mediated killing in presence of normal human serum. Conversely, naturally serum sensitive strains that did not display a significant polyP pseudo-capsule became resistant to complement in the presence of exogenous polyP. The presence of polyP pseudo-capsule was also critical in the protection from antibacterial activity of cationic antimicrobial peptide, such as cathelicidin LL-37. Results showed that the minimum bactericidal concentration was lower in strains lacking polyP than in those harboring the pseudo-capsule. Data referring to phagocytic killing resistance, assessed by using neutrophil-like cells, showed a significant decrease in viability of mutants lacking polyP on their cell surface in comparison to the wild-type strain. The addition of exogenous polyP overturned the killing phenotype of sensitive strains suggesting that gonococcus could exploit environmental polyP to survive to complement-mediated, cathelicidin and intracellular killing. Taken together, data presented here indicate an essential role of the polyP pseudo-capsule in the gonococcal pathogenesis, opening new perspective on gonococcal biology and more effective treatments.

Natural proteoglycan receptor analogs determine the dynamics of Opa adhesin-mediated gonococcal infection of Chang epithelial cells

Many bacterial pathogens possess a complex machinery for the induction and/or secretion of factors that promote their uptake by mammalian cells. We searched for the molecular basis of the 60- to 90-min lag time in the interaction of Neisseria gonorrhoeae carrying the heparin-binding Opa adhesin with Chang epithelial cells. Infection assays in the presence of chloramphenicol demonstrated that the Opa-mediated gonococcal infection of Chang cells required bacterial protein synthesis when the microorganisms were derived from GC agar but not when grown in liquid media. Further analysis indicated that contact with agar ingredients rather than the growth state of the microorganisms determined the infection dynamics. DEAE chromatography of GC agar extracts and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses and testing of collected fractions in infection assays identified negatively charged high-molecular-weight polysaccharides in the agar as inhibitors of the cellular infection. Electron microscopy showed that agar-grown gonococci were surrounded by a coat of alcian blue-positive material, probably representing accreted polysaccharides. Similar antiphagocytic material was isolated from bovine serum, indicating that in biological fluids gonococci producing the heparin-binding Opa adhesin may become covered with externally derived polysaccharides as well. Binding assays with gonococci and epithelial proteoglycan receptors revealed that polysaccharides derived from agar or serum compete with the proteoglycans for binding of the heparin-binding Opa adhesin and thus act as receptor analogs. Growth of gonococci in a polysaccharide-free environment resulted in optimal proteoglycan receptor binding and rapid bacterial entry into Chang cells. The recognition that gonococci with certain phenotypes can recruit surface polysaccharides that determine in vitro infection dynamics adds a different dimension to the well-recognized biological significance of genetic variation for this pathogen.

Role of oxidants in microbial pathophysiology

Reactive oxidant species (superoxide, hydrogen peroxide, hydroxyl radical, hypohalous acid, and nitric oxide) are involved in many of the complex interactions between the invading microorganism and its host. Regardless of the source of these compounds or whether they are produced under normal conditions or those of oxidative stress, these oxidants exhibit a broad range of toxic effects to biomolecules that are essential for cell survival. Production of these oxidants by microorganisms enables them to have a survival advantage in their environment. Host oxidant production, especially by phagocytes, is a counteractive mechanism aimed at microbial killing. However, this mechanism may be contribute to a deleterious consequence of oxidant exposure, i.e., inflammatory tissue injury. Both the host and the microorganism have evolved complex adaptive mechanisms to deflect oxidant-mediated damage, including enzymatic and nonenzymatic oxidant-scavenging systems. This review discusses the formation of reactive oxidant species in vivo and how they mediate many of the processes involved in the complex interplay between microbial invasion and host defense.

Cloning and characterization of the meningococcal polyphosphate kinase gene: production of polyphosphate synthesis mutants

The pathogenic Neisseria species accumulate polyphosphate to levels between 10 and 20% of their total phosphate content. However, the significance of this compound for the growth and pathogenicity of these species is not understood. A previous report (C.R. Tinsley, B.N. Manjula, and E.C. Gotschlich, Infect. Immun. 61:3703-3710, 1993) describes the purification of polyphosphate kinase, the enzyme responsible for synthesis of polyphosphate, from Neisseria meningitidis BNCV. By use of probes based on the amino acid sequence of the purified enzyme, the structural gene ppk has been cloned and sequenced. The coding sequence is 2,055 bp long and codes for a protein of 77.2 kDa. The open reading frame of the cloned gene was interrupted by the insertion of a kanamycin resistance cassette, and ppk mutants were obtained in both Neisseria gonorrhoeae and N. meningitidis by transformation with the recombinant plasmid. Amounts of polyphosphate in the ppk mutants were reduced to between 2 and 10% of wild-type levels. The mutants grew less vigorously than wild-type organisms in vitro and showed a striking increase in sensitivity to killing by human serum.

Purification and characterization of polyphosphate kinase from Neisseria meningitidis

The important human pathogens Neisseria meningitidis and Neisseria gonorrhoeae accumulate phosphate in the form of polyphosphate (A. Noegel and E. C. Gotschlich, J. Exp. Med. 157:2049-2060, 1983), and the localization of more than half of this long-chain polymer on the exterior of the cells suggests a function as a protective, capsule-like coating. To enable further genetic investigation of the role of polyphosphate in Neisseria spp., the enzyme polyphosphate kinase (PPK), which catalyzes the synthesis of polyphosphate from ATP, was purified from N. meningitidis BNCV. The activity is dependent on Mg2+ and phosphate or polyphosphate and is inhibited by ADP. The Km for ATP is 1.5 mM, and the turnover number is 47 phosphate residues per polypeptide per s. Analysis of PPK labelled with [gamma-32P]ATP indicates that the enzyme is phosphorylated during the reaction, probably at an arginine residue. N-terminal and two internal amino acid sequences were derived from the purified protein and will allow the design of synthetic oligonucleotides for cloning and genetic manipulation of the ppk gene.

Phagocytosis of virulent Porphyromonas gingivalis by human polymorphonuclear leukocytes requires specific immunoglobulin G

No studies to date clearly define the interactions between Porphyromonas gingivalis and human peripheral blood polymorphonuclear leukocytes (PMN), nor has a protective role for antibody to P. gingivalis been defined. Using a fluorochrome phagocytosis microassay, we investigated PMN phagocytosis and killing of P. gingivalis as a function of P. gingivalis-specific antibody. Sera from a nonimmune rabbit and a healthy human subject were not opsonic for virulent P. gingivalis A7436, W83, and HG405; phagocytosis of these strains (but not 33277) required opsonization with hyperimmune antiserum (RaPg). Diluting RaPg with a constant complement source decreased proportionally the number of P. gingivalis A7436 cells phagocytosed per phagocytic PMN. Enriching for the immunoglobulin G fraction of RAPg A7436 enriched for opsonic activity toward A7436. An opsonic evaluation of 18 serum samples from adult periodontitis patients revealed that only 3 adult periodontitis sera of 17 with elevated immunoglobulin G to P. gingivalis A7436 were opsonic for A7436 and, moreover, that the serum sample with the highest enzyme-linked immunosorbent assay titer was most opsonic (patient 1). However, the opsonic activity of serum from patient 1 was qualitatively and not just quantitatively different from that of the nonopsonic human sera (but was less effective opsonin than RaPg). Strain variability was observed in resistance of P. gingivalis to phagocytosis, and opsonization was strain specific for some, but not all, strains tested. An evaluation of killing of A7436 revealed that serum killing and extracellular killing of P. gingivalis were less effective alone when compared with intracellular PMN killing alone.

Possible presence of a capsule in Branhamella catarrhalis

Clinical isolates of Branhamella catarrhalis from patients with respiratory infections were used in this study. Electron microscopic observation after treating Branhamella catarrhalis with immune serum and ruthenium red revealed the capsule. In the phagocytosis test, most organisms were not ingested by human polymorphonuclear neutrophils in the presence of normal rabbit serum (NRS), while organisms were primarily cell associated and apparently ingested in the presence of immunized rabbit serum (IRS). The capsule may be one of the virulence factors in this bacteria. This study demonstrates the possible presence of a capsule in Branhamella catarrhalis.

Biology of Haemophilus ducreyi

The etiological agent of the sexually transmitted genital ulcer disease chancroid was first described in 1889 by Auguste Ducrey following repeated autoinoculation of purulent ulcer material from a series of patients. The organism was isolated on artificial media a decade later but has remained difficult to isolate consistently, resulting in controversy over its characteristics and role as the causative agent of chancroid. Because of its fastidious growth requirements, including unknown components in blood, the organism was included in the original description of the genus Haemophilus. Requirement for exogenous hemin and limited phenotypic characteristics, including structural and antigenic properties, suggested that Haemophilus ducreyi was a valid member of the genus Haemophilus. Recent studies of respiratory quinones, deoxyribonucleic acid hybridization, and competition for homologous transformation of the type species, H. influenzae, suggest that H. ducreyi is unrelated to any of the present species of the family Pasteurellaceae, which includes members of the genera Haemophilus, Actinobacillus, and Pasteurella. This review summarizes the early studies with H. ducreyi and our current knowledge of the microbiology of this important human pathogen.

Attempts to demonstrate a polysaccharide capsule in Neisseria gonorrhoeae

The presence or absence of a polysaccharide capsule on the human pathogen Neisseria (N.) gonorrhoeae is still a topic of controversy. For this reason we compared the results obtained by light microscopy (dry India ink-Fuchsin stain) and electron microscopy (Alcian blue-lanthanum nitrate stain) of encapsulated strains of N. meningitidis and Streptococcus (S.) pneumoniae and of non-encapsulated strains of S. pneumoniae and Escherichia (E.) coli with those obtained using the same methods on strains of pilliated and non-pilliated N. gonorrhoeae. After staining with India ink-Fuchsin no capsules could be demonstrated on any of the N. gonorrhoeae strains studied. If present the capsules on these cells are too delicate to be identified by light microscopy. After treatment with Alcian blue-lanthanum nitrate sections of cells of N. meningitidis and S. pneumoniae generally showed the presence of a capsular layer. Sections of cells of the non-encapsulated strain of S. pneumoniae which possess C (common)-polysaccharide also showed surface associated capsule-like material. Similarly the surface of the cells of the E. coli strain showed material which appeared to be tufts of pili and/or M (mucoid)-antigen. In experiments where the N. gonorrhoeae cells were harvested as early as after six hours of growth a capsule-like material was demonstrated on cells of all strains studied.

Presence of a capsule in Neisseria lactamica, antigenically similar to the capsule of N. meningitidis

Three of thirteen strains of Neisseria lactamica, a species closely related to N. meningitidis, were selected on the basis of their ability to be strongly agglutinated by serogroup B antimeningococcal serum. The presence of a capsule was demonstrated using Alcian blue as a stain for acidic polysaccharide. When reacted with serogroup B antimeningococcal sera, 2 out of 3 N. lactamica B-coagglutanating strains exhibited an extracellular material comparable in size, antigenicity and staining properties to the capsule of serogroup B N. meningitidis.

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.

Major heat-modifiable outer membrane protein in gram-negative bacteria: comparison with the ompA protein of Escherichia coli

The outer membranes of several strains of Escherichia coli, other enteric bacteria, and a variety of nonenteric gram-negative bacteria all contain a major heat-modifiable protein similar to the OmpA protein of E. coli K-12. The heat-modifiable proteins from these bacteria resemble the K-12 protein in molecular weight, in preferential release from the outer membrane by sodium dodecyl sulfate in the presence of Mg2+, and in characteristic cleavage by proteases to yield a smaller fragment which remains membrane bound. Antiserum directed against the K-12 protein precipitated the heat-modifiable protein from all strains of Enterobacteriaceae, and chemical comparison by isoelectric focusing, cyanogen bromide cleavage profiles, and proteolytic peptide analysis indicated that the proteins from the various enteric bacteria were nearly identical in primary structure. The heat-modifiable proteins from bacteria phylogenically distant from E. coli shared many of the properties of the E. coli protein but were chemically distinct. Thus, it appears that the structure (and, presumably, the function) of the heat-modifiable protein of gram-negative bacteria is strongly conserved during evolution.

The biology of the gonococcus

Gonorrhea has been known since antiquity. Today, this disease is the most commonly reported infectious disease in the U.S. The natural environment of the etiological agent, Neisseria gonorrhoeae, is man. In this host, the organism usually parasitizes mucosal surfaces populated by columnar epithelial cells. Under certain conditions, the gonococcus may disseminate or spread to adjacent organs. The gonococcus is well adapted to its environment and is a successful parasite. Until recently, gonococci were uniformly sensitive to penicilin. However, a plasmid encoding beta-lactamase has been identified in some isolates. Most strains exhibit specific requirements for various amino acids, vitamins, purines, and pyrimidines. Only glucose, pyruvate, and lactate are utilized as sources of energy. Glucose is dissimilated by a combination of the Entner-Doudoroff and pentose phosphate pathways. A tricarboxylic acid cycle is also present and active under certain conditions. Structurally, the cell envelope of the gonococcus resembles that of a typical Gram-negative bacterium. Gonococci are highly autolytic, especially in older cultures or after depletion of the energy source. Autolysis is not due solely to peptidoglycan hydrolysis, but appears to involve a destabilization of the outer membrane as well. Cell surface components such as pili, lipopolysaccharide, outer membrane proteins, and a capsule are associated with the virulence and pathogenicity of this organism.