Presence of antibodies to the major anaerobically induced gonococcal outer membrane protein in sera from patients with gonococcal infections

Interaction of pathogenic Neisseria with host defenses. What happens in vivo?

N. gonorrhoeae initiates infection by adhering to and invading columnar epithelial cells. Over time these activities often induce inflammation, with the influx of neutrophils and serum into the urethral lumen, cervical os, conjunctiva, and the like. At least some of these infected niches contain CMP-NANA (cytidine monophospho-N-acetyl neuraminic acid, also called CMP-sialic), contain sialylated gonococci, and are relatively or strictly anaerobic due to neutrophil and gonococcal metabolism and to the site of disease, that is, the peritoneal cavity. Gonococci thus encounter environmental conditions, reagents, and substrates in the human body that are not normally present in vitro. Knapp and Clark were the first to successfully grow gonococci anaerobically in an easily reproducible system, allowing researchers to begin to investigate in vitro the effects of anaerobiosis on gonococcal virulence traits. As a result of a series of elegant and in depth studies, Smith and Parsons and their colleagues showed that growth in CMP-NANA confers on the gonococcus a high degree of phenotypic (readily reversible) serum resistance and that CMP-NANA is available in vivo at sites of gonococcal infection and disease; gonococci become covalently coated with sialic acid and they become serum resistant (reviewed in refs. 8-10). Given that gonococci growing in the absence of oxygen or in the presence of CMP-NANA probably more closely resemble gonococci growing inside the human host, we studied several possible virulence traits of gonococci cultivated under these conditions. We first observed that anaerobic growth (in the absence of CMP-NANA) increases gonococcal resistance to killing by low (but not high) concentrations of normal human serum. We also asked whether anaerobic growth affected gonococcal association with host cells. Contrary to the effects on serum killing, anaerobic growth (in the absence of CMP-NANA) does not appear to affect the ability of gonococci (expressing certain adhesive outer membrane proteins called Opa proteins) to bind to and enter human epithelial cell lines or to bind to or resist killing by human neutrophils. The results from studies investigating the modulatory role of CMP-NANA were more striking. Growth in CMP-NANA dramatically inhibits the adherence of Opa+ gonococci to human neutrophils. It does not, however, appear to significantly decrease their sensitivity to phagocytic killing or to in vitro killing by lysosomal contents (aqueous extracts of human neutrophil granules).(ABSTRACT TRUNCATED AT 400 WORDS)

Variation in hydrogen peroxide sensitivity between different strains of Neisseria gonorrhoeae is dependent on factors in addition to catalase activity

Catalase, which catalyzes the reduction of hydrogen peroxide to oxygen and water, is considered the primary defense of Neisseria gonorrhoeae against exogenous hydrogen peroxide. Recent reports have demonstrated drastically different sensitivities of the organism to hydrogen peroxide ranging from greater than 80% survival after challenge with 30 mM hydrogen peroxide to less than 0.001% survival after challenge with 10 mM hydrogen peroxide. In this study, we have examined the hydrogen peroxide sensitivities of six clinical gonococcal isolates. The study demonstrates that the variations in gonococcal hydrogen peroxide sensitivities previously reported can be attributed to (i) differences in experimental methods employed or (ii) variation among different gonococcal strains. All of the gonococcal isolates examined generated similar concentrations of catalase, implying that the differences in the H2O2 sensitivity observed may depend on factors in addition to catalase.

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.

Signal transduction and virulence regulation in human and animal pathogens

Pathogens have developed many strategies for survival in animals and humans which possess very effective defense mechanisms. Although there are many different ways, in which pathogenic bacteria solved the problem to overcome the host defense, some common features of virulence mechanisms can be detected even in phylogenetically very distant bacteria (Finlay and Falkow (1989) Microb. Rev. 6, 1375-1383). One important feature is that the regulation of expression of virulence factors and the exact timing of their expression is very important for many of the pathogenic bacteria, as most of them have to encounter different growth situations during an infection cycle, which require a fast adaptation to the new situation by the expression of different factors. This review gives an overview about the mechanisms used by pathogenic bacteria to accomplish the difficult task of regulation of their virulence potential in response to environmental changes. In addition, the relationship of these virulence regulatory systems with other signal transduction mechanisms not involved in pathogenicity is discussed.

Isolation and nucleotide sequence of the gene (aniA) encoding the major anaerobically induced outer membrane protein of Neisseria gonorrhoeae

When grown under anaerobic conditions, Neisseria gonorrhoeae, the etiologic agent of the sexually transmitted disease gonorrhea, expresses several novel outer membrane proteins. One of these, Pan 1, has an apparent molecular mass of 54 kDa in electrophoresis and is recognized by serum samples from patients with gonococcal infection. The presence of antibodies to this protein in patient sera suggests that Pan 1 is expressed during gonococcal infection and, more importantly, that N. gonorrhoeae grows anaerobically in vivo. We have cloned the Pan 1 structural gene, aniA, by screening a gonococcal lambda gt11 expression library with monospecific, polyclonal anti-Pan 1 antiserum. Three distinct immunoreactive recombinants, containing overlapping fragments of DNA, were isolated and confirmed to be coding for Pan 1 protein sequences. Northern (RNA blot) hybridization of an insert from an aniA recombinant to total gonococcal cellular RNA revealed the presence of a 1.5-kb transcript that was specific to RNA from anaerobically grown gonococci, indicating that the aniA gene is regulated at the transcriptional level and is monocistronic. To characterize the aniA gene, we have sequenced the entire 2-kb region spanned by the overlapping recombinants. We have also performed primer extension analysis on RNA isolated from aerobically and anaerobically grown gonococci in order to define the aniA promoter region. Two putative primer extension products specific to organisms grown anaerobically were identified by homology to known Escherichia coli promoter sequences, suggesting that the regulation of aniA expression involves multiple promoter regions.

The major anaerobically induced outer membrane protein of Neisseria gonorrhoeae, Pan 1, is a lipoprotein

Pan 1 is an acidic outer membrane protein of Neisseria gonorrhoeae that is expressed only when gonococci are grown anaerobically. On silver-stained sodium dodecyl sulfate-polyacrylamide gels, Pan 1 migrates as an intense but diffuse 54-kDa protein. The deduced amino acid sequence of Pan 1 from the aniA (anaerobically induced protein) open reading frame reveals a lipoprotein consensus sequence, Ala-Leu-Ala-Ala-Cys, and a processed molecular mass of 39 kDa. Furthermore, there is strong homology at the N terminus and C terminus of Pan 1 to the termini of the gonococcal outer membrane lipoproteins Lip and Laz. [3H]palmitic acid labeling of gonococci grown under oxygen-limited conditions demonstrated specific incorporation of label into Pan 1, suggesting further that Pan 1 is a lipoprotein.

Identification and molecular analysis of a 63-kilodalton stress protein from Neisseria gonorrhoeae

Iron limitation, glucose deprivation, and growth under low oxygen supply (environmental stress) increased the expression of several proteins of Neisseria gonorrhoeae, including a 63-kilodalton protein identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This gonococcal stress protein (GSP63) was detected in the cytosol and copurified with lithium acetate-derived outer membranes. Successful purification of the protein was achieved by sucrose density gradient centrifugation and by chromatography on phenyl-Sepharose. Gel filtration of the purified protein revealed a molecular weight of approximately 450,000, suggesting that in its native state, the protein consists of a multimer of six to eight subunits. Isoelectric focusing indicated a pI of 5.2. Immunoblotting experiments using a polyclonal antiserum raised against the purified protein demonstrated cross-reactivity with a protein of the same electrophoretic mobility as GSP63 in all eight gonococcal isolates tested. N-terminal amino acid sequencing of the protein revealed up to 65% homology with members of the Hsp60 heat shock protein family, suggesting that GSP63 is related to this group of proteins. This relationship was further substantiated by the immunological cross-reactivity of GSP63 with mycobacterial Hsp60 and the ATP-binding activity of the gonococcal stress protein.

Regulation of catalase in Neisseria gonorrhoeae. Effects of oxidant stress and exposure to human neutrophils

We studied the effects of oxidant stress on the catalase activity and hydrogen peroxide sensitivity of Neisseria gonorrhoeae. N. gonorrhoeae is an obligate pathogen of man that evokes a remarkable but ineffective neutrophil response. Gonococci make no superoxide dismutase but express high catalase activity. Gonococcal catalase activity increased threefold when organisms were subjected to 1.0 mM hydrogen peroxide. This increase in catalase activity was marked by a parallel increase in protein concentration recognized by a rabbit polyclonal antibody raised against the purified gonococcal enzyme. Catalase was primarily localized to the gonococcal cytoplasm in the presence or absence of stress; only a single isoenzyme of catalase could be identified. Exposure of gonococci to neutrophil-derived oxidants was accomplished by stimulating neutrophils with phorbol myristate acetate or by using gonococcal Opa variants that interacted with neutrophils with different degrees of efficiency. Gonococci exposed to neutrophils demonstrated a twofold increase in catalase activity in spite of some reduction in viability. Exposure of gonococci to 1.0 mM hydrogen peroxide made the organisms significantly more resistant to higher concentrations of hydrogen peroxide and to neutrophils than control organisms. These results suggest that catalase is an important defense for N. gonorrhoeae during attack by human neutrophils. The rapid response of this enzyme to hydrogen peroxide should be taken into consideration in studies designed to evaluate the interaction between neutrophils and gonococci.

Anaerobic growth of gonococci does not alter their Opa-mediated interactions with human neutrophils

Gonococci grown anaerobically (anaerobic gonococci) in the presence of nitrite induce the expression of at least three novel outer membrane proteins (PANs 1 to 3). Although PAN 1 is expressed by gonococci during gonorrhea, the function of the PAN proteins remains unknown. In the absence of serum, gonococci possessing opacity-associated (Opa, formerly PII) outer membrane proteins adhere to, stimulate, and are phagocytically killed by human neutrophils. Gonococci lacking Opa proteins demonstrate none of these activities. We investigated whether the PAN proteins, or any other characteristics of anaerobic gonococci, altered the ability of nonpiliated, Opa+ or Opa- gonococci to adhere to, stimulate, or be phagocytically killed by neutrophils. The expression of Opa4 by strain F62, as determined by its relative mobility on sodium dodecyl sulfate-polyacrylamide gels, appeared to be unaltered by anaerobic growth, as seen previously (V. L. Clark, L. A. Campbell, D. A. Palermo, T. M. Evans, and K. W. Klimpel, Infect Immun. 55:1359-1364, 1987). Anaerobic and aerobic Opa+ gonococci adhered to and stimulated neutrophils to the same extent. Similarly, anaerobic and aerobic Opa- gonococci adhered to and stimulated neutrophils equally poorly. Finally, anaerobic and aerobic Opa+ gonococci were equally sensitive to phagocytic killing by neutrophils, while anaerobic and aerobic Opa- gonococci were equally resistant to killing. Thus, the role of Opa proteins in mediating the interactions of gonococci with human neutrophils appears unaltered by anaerobic growth, and the PAN proteins, or other cryptic properties of anaerobic gonococci, do not seem to modulate or mediate these phenomena.

Distribution of a protein antigenically related to the major anaerobically induced gonococcal outer membrane protein among other Neisseria species

The Pan 1 protein of Neisseria gonorrhoeae is a novel 54-kDa outer membrane protein expressed only when gonococci are grown in the absence of oxygen. It is a major antigen recognized by sera from patients with gonococcal infection. We raised mouse monospecific polyclonal antiserum to gel-purified Pan 1 from gonococcal strain F62. The antiserum was broadly cross-reactive among gonococcal strains; all strains tested reacted in immunoblot analysis proportionate to the amount of Pan 1 visible in silver-stained sodium dodecyl sulfate (SDS)-polyacrylamide gels. In immunoblot experiments, N. lactamica and N. cinerea reacted very strongly to the anti-Pan 1 antiserum, whereas N. sicca, N. flava, and N. mucosa did not react at all. The other commensals tested, N. subflava and N. perflava, exhibited only a minor reaction. These results correlated with the apparent amount of Pan 1 seen on SDS-polyacrylamide gels of outer membranes. SDS-polyacrylamide gel analysis of six meningococcal strains revealed no visible anaerobically induced outer membrane proteins, and the subsequent immunoblots showed only slight or no reaction to the anti-Pan 1 antibody. In the four meningococcal strains that did react slightly with the antiserum, a Pan 1-like protein was seen only in anaerobically grown cells. Thus, meningococci did not express Pan 1 at levels comparable to that found in gonococci; however, when Pan 1 was expressed in meningococcal strains, it was oxygen regulated. This is the first example of a protein found in the gonococcal outer membrane that, under identical growth conditions, is not expressed at similar levels in the meningococcus.