Nitric oxide is not involved in Neisseria gonorrhoeae-induced cellular damage of human Fallopian tubes in vitro

In the present study, we investigated whether cellular damage, as demonstrated by lactate dehydrogenase (LDH) release in the human fallopian tube (FT) infected by Neisseria gonorrhoeae (Ngo), correlated with high levels of nitric oxide synthase (NOS) mRNA and enzyme activity. Infection with Ngo induced a significant increase (~35-fold) in mRNA transcripts of the inducible isoform of NOS. Paradoxically, a reduction in NOS enzyme activity was observed in infected cultures, suggesting that gonococcal infection possibly influences translation of iNOS mRNA to the enzyme. In addition, treatment with the NOS inhibitor TRIM did not prevent gonococcal-induced cellular damage. In contrast, the addition of the inhibitor L-NAME induced a 40% reduction in LDH release, which correlated with a ~50% reduction in gonococcal numbers. Moreover, treatment of normal FT explants with an exogenous NO donor, SNAP, did not induce significant cellular damage. Taken together, our data suggest that NO does not contribute to cellular damage during infection of the human FT with Neisseria gonorrhoeae.

Prevalence of Chlamydia trachomatis and Neisseria gonorrhoeae in HIV-seropositive patients and gonococcal antimicrobial susceptibility: an update in Thailand

We surveyed the rate of chlamydial and gonococcal infections among human immunodeficiency virus (HIV)-seropositive patients in Thailand as well as the current status of antimicrobial resistance of Neisseria gonorrhoeae and determined the prevalence of penicillinase-producing N. gonorrhoeae (PPNG) in Thailand. A total of 1,158 endocervical swabs from 824 HIV-seropositive patients were collected to detect both organisms by Gen-Probe. The prevalences of chlamydial and gonococcal infection were 9.7 and 1.3%, respectively. Susceptibility of 122 gonococcal isolates to 6 drugs was determined by the disk diffusion method. None of the isolates was susceptible to penicillin or tetracycline. With respect to fluoroquinolones, more than 90% of the isolates were resistant to ciprofloxacin and ofloxacin. No gonococcal isolate with resistance to cefotaxime and ceftriaxone was detected. Among the 122 isolates, 83.6% or 102 isolates were PPNG, and most (79.5%) of these 122 isolates were further identified as PPNG plus tetracycline-resistant N. gonorrhoeae, with only 4.1% being PPNG alone. All of the 102 isolates identified as PPNG contained the bla(TEM) gene. We then performed a preliminary molecular study and identified, for the first time in Thailand, a PPNG isolate producing beta-lactamase and containing the bla(TEM) gene which was identical to the beta-lactamase TEM protein of Salmonella enterica identified as TEM-135.

Mechanism of allosteric inhibition of N-acetyl-L-glutamate synthase by L-arginine

N-Acetylglutamate synthase (NAGS) catalyzes the first committed step in l-arginine biosynthesis in plants and micro-organisms and is subject to feedback inhibition by l-arginine. This study compares the crystal structures of NAGS from Neisseria gonorrhoeae (ngNAGS) in the inactive T-state with l-arginine bound and in the active R-state complexed with CoA and l-glutamate. Under all of the conditions examined, the enzyme consists of two stacked trimers. Each monomer has two domains: an amino acid kinase (AAK) domain with an AAK-like fold but lacking kinase activity and an N-acetyltransferase (NAT) domain homologous to other GCN5-related transferases. Binding of l-arginine to the AAK domain induces a global conformational change that increases the diameter of the hexamer by approximately 10 A and decreases its height by approximately 20A(.) AAK dimers move 5A outward along their 2-fold axes, and their tilt relative to the plane of the hexamer decreases by approximately 4 degrees . The NAT domains rotate approximately 109 degrees relative to AAK domains enabling new interdomain interactions. Interactions between AAK and NAT domains on different subunits also change. Local motions of several loops at the l-arginine-binding site enable the protein to close around the bound ligand, whereas several loops at the NAT active site become disordered, markedly reducing enzymatic specific activity.

The crystal structure of N-acetyl-L-glutamate synthase from Neisseria gonorrhoeae provides insights into mechanisms of catalysis and regulation

The crystal structures of N-acetylglutamate synthase (NAGS) in the arginine biosynthetic pathway of Neisseria gonorrhoeae complexed with acetyl-CoA and with CoA plus N-acetylglutamate have been determined at 2.5- and 2.6-A resolution, respectively. The monomer consists of two separately folded domains, an amino acid kinase (AAK) domain and an N-acetyltransferase (NAT) domain connected through a 10-A linker. The monomers assemble into a hexameric ring that consists of a trimer of dimers with 32-point symmetry, inner and outer ring diameters of 20 and 100A, respectively, and a height of 110A(.) Each AAK domain interacts with the cognate domains of two adjacent monomers across two 2-fold symmetry axes and with the NAT domain from a second monomer of the adjacent dimer in the ring. The catalytic sites are located within the NAT domains. Three active site residues, Arg316, Arg425, and Ser427, anchor N-acetylglutamate in a position at the active site to form hydrogen bond interactions to the main chain nitrogen atoms of Cys356 and Leu314, and hydrophobic interactions to the side chains of Leu313 and Leu314. The mode of binding of acetyl-CoA and CoA is similar to other NAT family proteins. The AAK domain, although catalytically inactive, appears to bind arginine. This is the first reported crystal structure of any NAGS, and it provides insights into the catalytic function and arginine regulation of NAGS enzymes.

Surveillance of antimicrobial susceptibilities in Neisseria gonorrhoeae in Nanjing, China, 1999-2006

OBJECTIVE

To monitor the frequency and types of antibiotic resistance of Neisseria gonorrhoeae in Nanjing, China, between 1999 and 2006.

METHODS

beta-Lactamase production was determined by paper acidometric testing. Minimum inhibitory concentrations (MICs) to penicillin, ceftriaxone, tetracycline, ciprofloxacin, and spectinomycin were determined by agar plate dilution. Plasmid types were determined for TRNG and PPNG isolates by PCR.

RESULTS

One-thousand two-hundred and eight N. gonorrhoeae isolates were examined. The rate of PPNG rose from 8.0% (9 of 112) in 1999 to 57.36% (113 of 197) in 2004, and declined to 44.44% (88 of 198) in 2006. Prevalence of TRNG increased from 1.8% (2 of 112) in 1999 to 32.82% (65 of 198) in 2006. 99.23% (258 of 260) of TRNG contained the Dutch-type tetM gene and 2 strains contained the American-type tetM gene. All PPNG examined contained the Asian type plasmid. Among non-PPNG, chromosomally mediated resistance to penicillin varied from 57.84% (59 of 102) to 87.80% (72 of 82). Chromosomal resistance to ciprofloxacin (QRNG) was detected in 83.93% (94 of 112) of the strains in 1999 and 98.99% (196 of 198) in 2006. Eight spectinomycin-resistant N. gonorrhoeae strains were detected between 2001 and 2006. None of the gonococcal isolates tested was resistant to ceftriaxone but decreased susceptibility was observed in some strains.

CONCLUSIONS

Among N. gonorrhoeae strains isolated in Nanjing, China, plasmid mediated resistance including PPNG and TRNG increased significantly between 1999 and 2006. Chromosomally mediated resistance to both penicillin and ciprofloxacin was also high during this period. Spectinomycin resistance of N. gonorrhoeae was sporadic. Ceftriaxone and spectinomycin can be considered effective antimicrobial agents for the treatment of gonorrhea in Nanjing at the present time.

A novel relaxase homologue is involved in chromosomal DNA processing for type IV secretion in Neisseria gonorrhoeae

The Neisseria gonorrhoeae type IV secretion system secretes chromosomal DNA that acts in natural transformation. To examine the mechanism of DNA processing for secretion, we made mutations in the putative relaxase gene traI and used nucleases to characterize the secreted DNA. The nuclease experiments demonstrated that the secreted DNA is single-stranded and blocked at the 5' end. Mutation of traI identified Tyr93 as required for DNA secretion, while substitution of Tyr201 resulted in intermediate levels of DNA secretion. TraI exhibits features of relaxases, but also has features that are absent in previously characterized relaxases, including an HD phosphohydrolase domain and an N-terminal hydrophobic region. The HD domain residue Asp120 was required for wild-type levels of DNA secretion. Subcellular localization studies demonstrated that the TraI N-terminal region promotes membrane interaction. We propose that Tyr93 initiates DNA processing and Tyr201 is required for termination or acts in DNA binding. Disruption of an inverted-repeat sequence eliminated DNA secretion, suggesting that this sequence may serve as the origin of transfer for chromosomal DNA secretion. The TraI domain architecture, although not previously described, is present in 53 uncharacterized proteins, suggesting that the mechanism of TraI function is a widespread process for DNA donation.

Neisseria gonorrhoeae O-linked pilin glycosylation: functional analyses define both the biosynthetic pathway and glycan structure

Neisseria gonorrhoeae expresses an O-linked protein glycosylation pathway that targets PilE, the major pilin subunit protein of the Type IV pilus colonization factor. Efforts to define glycan structure and thus the functions of pilin glycosylation (Pgl) components at the molecular level have been hindered by the lack of sensitive methodologies. Here, we utilized a 'top-down' mass spectrometric approach to characterize glycan status using intact pilin protein from isogenic mutants. These structural data enabled us to directly infer the function of six components required for pilin glycosylation and to define the glycan repertoire of strain N400. Additionally, we found that the N. gonorrhoeae pilin glycan is O-acetylated, and identified an enzyme essential for this unique modification. We also identified the N. gonorrhoeae pilin oligosaccharyltransferase using bioinformatics and confirmed its role in pilin glycosylation by directed mutagenesis. Finally, we examined the effects of expressing the PglA glycosyltransferase from the Campylobacter jejuni N-linked glycosylation system that adds N-acetylgalactosamine onto undecaprenylpyrophosphate-linked bacillosamine. The results indicate that the C. jejuni and N. gonorrhoeae pathways can interact in the synthesis of O-linked di- and trisaccharides, and therefore provide the first experimental evidence that biosynthesis of the N. gonorrhoeae pilin glycan involves a lipid-linked oligosaccharide precursor. Together, these findings underpin more detailed studies of pilin glycosylation biology in both N. gonorrhoeae and N. meningitidis, and demonstrate how components of bacterial O- and N-linked pathways can be combined in novel glycoengineering strategies.

AtlA functions as a peptidoglycan lytic transglycosylase in the Neisseria gonorrhoeae type IV secretion system

Type IV secretion systems require peptidoglycan lytic transglycosylases for efficient secretion, but the function of these enzymes is not clear. The type IV secretion system gene cluster of Neisseria gonorrhoeae encodes two peptidoglycan transglycosylase homologues. One, LtgX, is similar to peptidoglycan transglycosylases from other type IV secretion systems. The other, AtlA, is similar to endolysins from bacteriophages and is not similar to any described type IV secretion component. We characterized the enzymatic function of AtlA in order to examine its role in the type IV secretion system. Purified AtlA was found to degrade macromolecular peptidoglycan and to produce 1,6-anhydro peptidoglycan monomers, characteristic of lytic transglycosylase activity. We found that AtlA can functionally replace the lambda endolysin to lyse Escherichia coli. In contrast, a sensitive measure of lysis demonstrated that AtlA does not lyse gonococci expressing it or gonococci cocultured with an AtlA-expressing strain. The gonococcal type IV secretion system secretes DNA during growth. A deletion of ltgX or a substitution in the putative active site of AtlA severely decreased DNA secretion. These results indicate that AtlA and LtgX are actively involved in type IV secretion and that AtlA is not involved in lysis of gonococci to release DNA. This is the first demonstration that a type IV secretion peptidoglycanase has lytic transglycosylase activity. These data show that AtlA plays a role in type IV secretion of DNA that requires peptidoglycan breakdown without cell lysis.

Neisseria gonorrheae O-Acetylpeptidoglycan Esterase, a Serine Esterase with a Ser-His-Asp Catalytic Triad

O-Acetylpeptidoglycan esterase from Neisseria gonorrheae FA1090 is similar in sequence to family CE-3 carbohydrate esterases of the CAZy classification system, and it functions to release O-linked acetyl groups from the C-6 position of muramoyl residues in O-acetylated peptidoglycan. Here, we characterize the peptidoglycan of N. gonorrheae FA1090 as being O-acetylated and find that it serves as a substrate for the esterase. The influence of pH on the activity of O-acetylpeptidoglycan esterase was determined, and pKa values of 6.38 and 6.78 for the enzyme-substrate complex (VEt-1) and free enzyme (VEt-1KM-1), respectively, were calculated. The enzyme was inactivated by sulfonyl fluorides but not by EDTA. Multiple-sequence alignment of the O-acetylpeptidoglycan esterase family 1 enzymes with members of the CE-3 enzymes and protein modeling studies identified Ser80, Asp366, and His369 as three invariant amino acid residues that could potentially serve as a catalytic triad. Replacement of each with alanine was accomplished by site-directed mutagenesis, and the resulting mutant proteins were purified to apparent homogeneity. The specific activity of each of the three esterase derivatives was greatly reduced on O-acetylpeptidoglycan. Using the artificial substrate p-nitrophenyl acetate, a kinetic analysis revealed that the turnover number (VEt-1) but not KM was affected by the replacements. These data thus indicate that N. gonorrheae O-acetylpeptidoglycan esterase, and by analogy the CE-3 family of enzymes, function as serine esterases involving a Ser-His-Asp catalytic triad.

Neisseria gonorrhoeae catalase is not required for experimental genital tract infection despite the induction of a localized neutrophil response

Neisseria gonorrhoeae produces several antioxidant defenses, including high levels of catalase, which may facilitate the persistence during an inflammatory response via neutralization of H2O2 produced by phagocytes. In vivo testing of the role of catalase in gonococcal survival is critical since several physiological factors impact interactions between N. gonorrhoeae and polymorphonuclear leukocytes (PMNs). Here we assessed the importance of gonococcal catalase in a surrogate model of female genital tract infection. Female BALB/c mice were treated with 17-beta estradiol to promote susceptibility to N. gonorrhoeae and inoculated intravaginally with wild-type gonococci or a catalase (kat) deletion mutant. A localized PMN influx occurred in an average of 43 and 81% of mice infected with wild-type or kat mutant gonococci, respectively, and PMNs associated with numerous wild-type or catalase-deficient bacteria were observed in vaginal smears. The combined results of six experiments showed a significant difference in the number of days wild-type bacteria were recovered compared to the catalase-deficient gonococci. However, there was much variability between experiments, and we found no correlation between PMN influx, colonization load, and clearance of wild-type or kat mutant bacteria. Estradiol treatment did not impair bacterial uptake, the luminol-dependent chemiluminescence response, or the killing capacity of isolated murine PMNs against N. gonorrhoeae or Staphylococcus aureus. Our data suggest N. gonorrhoeae is not significantly challenged by H2O2 produced by PMNs in the murine lower genital tract; alternatively, redundant defense mechanisms may protect the gonococcus from reactive oxygen species during infection.

Evidence for distinctive mechanisms of S-nitrosoglutathione metabolism by AdhC in two closely related species, Neisseria gonorrhoeae and Neisseria meningitidis

The adhC gene from 11 strains of Neisseria gonorrhoeae was distinguished from its homologue in Neisseria meningitidis by the presence of a premature stop codon caused by a single base insertion. Mutational analysis showed that NADH S-nitrosoglutathione oxidoreductase activity was associated with adhC in Neisseria meningitidis but not in Neisseria gonorrhoeae.

Lactate acquisition promotes successful colonization of the murine genital tract by Neisseria gonorrhoeae

Previous studies on Neisseria gonorrhoeae have demonstrated that metabolism of lactate in the presence of glucose increases the growth rate of the bacterium and enhances its resistance to complement-mediated killing. Although these findings in vitro suggest that the acquisition of lactate promotes gonococcal colonization, the significance of this carbon source to the survival of the gonococcus in vivo remains unknown. To investigate the importance of lactate utilization during Neisseria gonorrhoeae genital tract infection, we identified the gene lctP, which encodes the gonococcal lactate permease. A mutant that lacks a functional copy of lctP was unable to take up exogenous lactate and did not grow in defined medium with lactate as the sole carbon source, in contrast to the wild-type and complemented strains; the mutant strain exhibited no growth defect in defined medium containing glucose. In defined medium containing physiological concentrations of lactate and glucose, the lctP mutant demonstrated reduced early growth and increased sensitivity to complement-mediated killing compared with the wild-type strain; the enhanced susceptibility to complement was associated with a reduction in lipopolysaccharide sialylation of the lctP mutant. The importance of lactate utilization during colonization was evaluated in the murine model of lower genital tract infection. The lctP mutant was significantly attenuated in its ability to colonize and survive in the genital tract, while the complemented mutant exhibited no defect for colonization. Lactate is a micronutrient in the genital tract that contributes to the survival of the gonococcus.

Discovery of a New Prokaryotic Type I GTP Cyclohydrolase Family

GTP cyclohydrolase I (GCYH-I) is the first enzyme of the de novo tetrahydrofolate biosynthetic pathway present in bacteria, fungi, and plants, and encoded in Escherichia coli by the folE gene. It is also the first enzyme of the biopterin (BH4) pathway in Homo sapiens, where it is encoded by a homologous folE gene. A homology-based search of GCYH-I orthologs in all sequenced bacteria revealed a group of microbes, including several clinically important pathogens, that encoded all of the enzymes of the tetrahydrofolate biosynthesis pathway but GCYH-I, suggesting that an alternate family was present in these organisms. A prediction based on phylogenetic occurrence and physical clustering identified the COG1469 family as a potential candidate for this missing enzyme family. The GCYH-I activity of COG1469 family proteins from a variety of sources (Thermotoga maritima, Bacillus subtilis, Acinetobacter baylyi, and Neisseria gonorrhoeae) was experimentally verified in vivo and/or in vitro. Although there is no detectable sequence homology with the canonical GCYH-I, protein fold recognition based on sequence profiles, secondary structure, and solvation potential information suggests that, like GCYH-I proteins, COG1469 proteins are members of the tunnel-fold (T-fold) structural superfamily. This new GCYH-I family is found in approximately 20% of sequenced bacteria and is prevalent in Archaea, but the family is to this date absent in Eukarya.

Reactivity of Penicillin-Binding Proteins with Peptidoglycan-Mimetic β-Lactams: What's Wrong with These Enzymes?

Beta-lactams exert their antibiotic action through their inhibition of bacterial DD-peptidases (penicillin-binding proteins). Bacteria, in general, carry several such enzymes localized on the outside of their cell membrane to catalyze the final step in cell wall (peptidoglycan) synthesis. They have been classified into two major groups, one of high molecular weight, the other of low. Members of the former group act as transpeptidases in vivo, and their inhibition by beta-lactams leads to cessation of bacterial growth. The latter group consists of DD-carboxypeptidases, and their inhibition by beta-lactams is generally not fatal to bacteria. We have previously shown that representatives of the former group are ineffective at catalyzing the hydrolysis/aminolysis of peptidoglycan-mimetic peptides in vitro [Anderson et al. (2003) Biochem. J. 373, 949-955]. The theme of these experiments is expanded in the present paper where we describe the synthesis of a series of beta-lactams (penicillins and cephalosporins) containing peptidoglycan-mimetic side chains and the kinetics of their inhibition of a panel of penicillin-binding proteins spanning the major classes (Escherichia coli PBP 2 and PBP 5, Streptococcus pneumoniae PBP 1b, PBP 2x and PBP 3, the Actinomadura R39 DD-peptidase, and the Streptomyces R61 DD-peptidase). The results of these experiments mirror and expand the previous results with peptides. Neither peptides nor beta-lactams with appropriate peptidoglycan-mimetic side chains react with the solubilized constructs of membrane-bound penicillin binding proteins (the first five enzymes above) at rates exceeding those of generic analogues. Such peptides and beta-lactams do react at greatly enhanced rates with certain soluble low molecular weight enzymes (R61 and R39 DD-peptidases). The former result is unexpected and interesting. Why do the majority of penicillin-binding proteins not recognize elements of local peptidoglycan structure? Possible answers are discussed. That this question needs to be asked casts fascinating shadows on current studies of penicillin-binding proteins for new drug design.

Characterization of the OxyR regulon of Neisseria gonorrhoeae

OxyR regulates the expression of the majority of H(2)O(2) responses in Gram-negative organisms. In a previous study we reported the OxyR-dependent derepression of catalase expression in the human pathogen Neisseria gonorrhoeae. In the present study we used microarray expression profiling of N. gonorrhoeae wild-type strain 1291 and an oxyR mutant strain to define the OxyR regulon. In addition to katA (encoding catalase), only one other locus displayed a greater than two-fold difference in expression in the wild type : oxyR comparison. This locus encodes an operon of two genes, a putative peroxiredoxin/glutaredoxin (Prx) and a putative glutathione oxidoreductase (Gor). Mutant strains were constructed in which each of these genes was inactivated. A previous biochemical study in Neisseria meningitidis had confirmed function of the glutaredoxin/peroxiredoxin. Assay of the wild-type 1291 cell free extract confirmed Gor activity, which was lost in the gor mutant strain. Phenotypic analysis of the prx mutant strain in H(2)O(2) killing assays revealed increased resistance, presumably due to upregulation of alternative defence mechanisms. The oxyR, prx and gor mutant strains were deficient in biofilm formation, and the oxyR and prx strains had decreased survival in cervical epithelial cells, indicating a key role for the OxyR regulon in these processes.

Dynamics of appearance and expansion of a prolyliminopeptidase- negative subtype among Neisseria gonorrhoeae isolates collected in Sydney, Australia, from 2002 to 2005

Recent studies have demonstrated a wide geographic circulation of isolates of Neisseria gonorrhoeae that fail to produce prolyliminopeptidase (PIP). Tests based on the production of this enzyme are important elements of a number of identification systems for gonococci. We documented the appearance, expansion, and contraction of subtypes of 165 PIP-negative gonococci detected in an extended and systematic sample of the 3,926 N. gonorrhoeae isolates collected in Sydney, Australia, from July 2002 to September 2005. Their appearance, peak, and decline followed an "epidemic" curve. At the peak of their prevalence in 2003, PIP-negative gonococci comprised 22% of all isolates. Closely related phenotypes accounted for 162/165 of the PIP-negative gonococci. Algorithms for confirmation of N. gonorrhoeae should take account of the temporal and geographic variability of gonococci by utilizing two or more distinct confirmatory methods.

AmiC functions as an N-acetylmuramyl-l-alanine amidase necessary for cell separation and can promote autolysis in Neisseria gonorrhoeae

Neisseria gonorrhoeae is prone to undergo autolysis under many conditions not conducive to growth. The role of autolysis during gonococcal infection is not known, but possible advantages for the bacterial population include provision of nutrients to a starving population, modulation of the host immune response by released cell components, and donation of DNA for natural transformation. Biochemical studies indicated that an N-acetylmuramyl-l-alanine amidase is responsible for cell wall breakdown during autolysis. In order to better understand autolysis and in hopes of creating a nonautolytic mutant, we mutated amiC, the gene for a putative peptidoglycan-degrading amidase in N. gonorrhoeae. Characterization of peptidoglycan fragments released during growth showed that an amiC mutant did not produce free disaccharide, consistent with a role for AmiC as an N-acetylmuramyl-l-alanine amidase. Compared to the wild-type parent, the mutant exhibited altered growth characteristics, including slowed exponential-phase growth, increased turbidity in stationary phase, and increased colony opacity. Thin-section electron micrographs showed that mutant cells did not fully separate but grew as clumps. Complementation of the amiC deletion mutant with wild-type amiC restored wild-type growth characteristics and transparent colony morphology. Overexpression of amiC resulted in increased cell lysis, supporting AmiC's purported function as a gonococcal autolysin. However, amiC mutants still underwent autolysis in stationary phase, indicating that other gonococcal enzymes are also involved in this process.

The prevalence of proline iminopeptidase negative Neisseria gonorrhoeae throughout England and Wales

BACKGROUND

The accurate laboratory identification of Neisseria gonorrhoeae is an essential element of the diagnosis of gonorrhoea and is particularly important for medicolegal cases. The detection of proline iminopeptidase (Pip) activity is widely used as a marker for gonococci, although Pip negative N gonorrhoeae isolates have been shown to generate false negative identifications when using biochemical kits. This study aimed to determine the frequency of Pip negative gonococci in England and Wales.

METHODS

A total of 2055 isolates were collected from consecutive patients attending 26 genitourinary medicine centres as part of the Gonococcal Resistance to Antimicrobials Surveillance Programme (GRASP). Upon receipt the identity of all isolates was confirmed using N gonorrhoeae specific monoclonal antibodies and the Pip status was determined using the Gonochek II kit.

RESULTS

The overall prevalence of Pip negative isolates was found to be 4.33%. Significant geographical variation was observed between isolates from centres outside London (p< or =0.001). Variation was also observed within London between the nine different clinics submitting isolates (p = 0.025). There was also a higher frequency of these isolates among men who have sex with men (p< or =0.001), which may account for geographical variations.

CONCLUSION

Pip negative N gonorrhoeae isolates are a very serious cause for concern as currently all biochemical test kits available within the United Kingdom require the presence of the Pip enzyme for an unambiguous identification of this pathogen. Raising awareness of the current prevalence of Pip negative N gonorrhoeae isolates is critical for the successful control of gonorrhoea.

Mobilization of the gonococcal 5.2 kb beta-lactamase plasmid pSJ5.2 into Escherichia coli by cointegration with several gram-conjugative plasmids

We report the mobilization by cointegration of the gonococcal 5.2 kb beta-lactamase plasmid pSJ5.2 in an Escherichia coli background. Transfer of pSJ5.2 was measured by filter mating assays with five different conjugative plasmids from Enterobacteriaceae and the gonococcal 41 kb tet(M). Plasmid pSJ5.2 was mobilized to E. coli at frequencies of 1.7x10(-6), 9.3x10(-8) and 2.7x10(-5) by the tet(M), R64 drd-33 and N3 conjugative plasmids, respectively. Mobilization of pSJ5.2 by the 41 kb tet(M) conjugative plasmid resulted in stable Amp(R) E. coli transconjugants consisting of pSJ5.2 plasmid with an insertion located in the 2.4 kb BamHI-BamHI fragment. Mobilization of pSJ5.2 by R64drd-33 and N3 conjugative plasmids involved stable cointegrates as detected by Southern Blot with a DIG-labelled PstI-digested pSJ5.2 probe. Restriction analysis of the R64::pSJ5.2 and N3::pSJ5.2 cointegrates and Southern Blot with the pSJ5.2 probe showed that cointegrates formed by deletion of DNA regions within the 1.8 kb BamHI-HindIII fragment of pSJ5.2. The plasmid thus appears to use multiple recombination mechanisms for cointegration with different conjugative plasmids. The complete nucleotide sequence of pSJ5.2 was determined, and will be a useful tool to further investigate the molecular mechanisms leading to its cointegrative transfer.

Neisseria gonorrhoeae PLD directly interacts with Akt kinase upon infection of primary, human, cervical epithelial cells

Neisseria gonorrhoeae secrets a phospholipase D (NgPLD), which augments complement receptor 3 (CR3)-mediated invasion of cervical epithelial cells. To elucidate the signalling pathways triggered with gonococcus CR3-engagement and the putative function of NgPLD in these events, we analysed the contribution of the phosphoinositide-Akt pathway to cervical infection. Our data indicated that Akt plays a critical role in cervical infection. Inhibition of myosin light chain kinase, PtdIns(4,5)P2, and Akt functions resulted in decreased gonococcus invasion of primary, human, cervical epithelial cells as well as Akt kinase activity. Akt activity was similarly impaired when cervical cells were challenged with NgPLD-mutant gonococci. Conversely, the PI3-kinase inhibitor, LY294002, enhanced gonococcal invasion of, and Akt activity within, primary cervical cells. We demonstrated that NgPLD directly binds to the Akt PH domain and can compete with a natural Akt ligand, PtdIns(3,4,5)P3, for Akt binding. Collectively, our data suggested that NgPLD augments gonococcus invasion of cervical epithelia by interacting with Akt kinase in a PI3-kinase-independent manner, which results in subversion of normal cervical cell signalling.

Sites in the CH3 Domain of Human IgA1 That Influence Sensitivity to Bacterial IgA1 Proteases

The influence of regions, other than the hinge, on the susceptibility of human IgA1 to cleavage by diverse bacterial IgA1 proteases, was examined using IgA1 mutants bearing amino acid deletions, substitutions, and domain swaps. IgA1 lacking the tailpiece retained its susceptibility to cleavage by all of the IgA1 proteases. The domain swap molecule alpha1alpha2gamma3, in which the CH3 domain of IgA1 was exchanged for that of human IgG1, was resistant to cleavage with the type 1 and 2 serine IgA1 proteases of Neisseria meningitidis, Neisseria gonorrhoeae, and Haemophilus influenzae, but remained sensitive to cleavage with the metallo-IgA1 proteases of Streptococcus pneumoniae, Streptococcus oralis, Streptococcus sanguis, and Streptococcus mitis. Substitution of the IgA1 Calpha3 domain motif Pro440 -Phe443 into the corresponding position in the Cgamma3 domain of alpha1alpha2gamma3 resulted now in sensitivity to the type 2 IgA1 protease of N. meningitidis, indicating the possible requirement of these amino acids for sensitivity to this protease. For the H. influenzae type 2 protease, resistance of an IgA1 mutant in which the CH3 domain residues 399-409 were exchanged with those from IgG1, but sensitivity of mutant HuBovalpha3 in which the Calpha3 domain of bovine IgA replaces that of human IgA1, suggests that CH3 domain residues Glu403, Gln406, and Thr409 influence sensitivity to this enzyme. Hence, unlike the situation with the metallo-IgA1 proteases of Streptococcus spp., the sensitivity of human IgA1 to cleavage with the serine IgA1 proteases of Neisseria and Haemophilus involves their binding to different sites specifically in the CH3 domain.

Neisseria gonorrhoeae DNA recombination and repair enzymes protect against oxidative damage caused by hydrogen peroxide

The strict human pathogen Neisseria gonorrhoeae is exposed to oxidative damage during infection. N. gonorrhoeae has many defenses that have been demonstrated to counteract oxidative damage. However, recN is the only DNA repair and recombination gene upregulated in response to hydrogen peroxide (H(2)O(2)) by microarray analysis and subsequently shown to be important for oxidative damage protection. We therefore tested the importance of RecA and DNA recombination and repair enzymes in conferring resistance to H(2)O(2) damage. recA mutants, as well as RecBCD (recB, recC, and recD) and RecF-like pathway mutants (recJ, recO, and recQ), all showed decreased resistance to H(2)O(2). Holliday junction processing mutants (ruvA, ruvC, and recG) showed decreased resistance to H(2)O(2) resistance as well. Finally, we show that RecA protein levels did not increase as a result of H(2)O(2) treatment. We propose that RecA, recombinational DNA repair, and branch migration are all important for H(2)O(2) resistance in N. gonorrhoeae but that constitutive levels of these enzymes are sufficient for providing protection against oxidative damage by H(2)O(2).

Alpha-2,3-sialyltransferase enhances Neisseria gonorrhoeae survival during experimental murine genital tract infection

The addition of host-derived sialic acid to Neisseria gonorrhoeae lipooligosaccharide is hypothesized to be an important mechanism by which gonococci evade host innate defenses. This hypothesis is based primarily on in vitro assays of complement-mediated and phagocytic killing. Here we report that a nonpolar alpha-2,3-sialyltransferase (lst) mutant of N. gonorrhoeae was significantly attenuated in its capacity to colonize the lower genital tract of 17-beta estradiol-treated female BALB/c mice during competitive infection with the wild-type strain. Genetic complementation of the lst mutation restored recovery of the mutant to wild-type levels. Studies with B10.D2-HC(o)H2(d)H(2)-T18c/OSN (C5-deficient) mice showed that attenuation of the lst mutant was not due to increased sensitivity to complement-mediated bacteriolysis, a result that is consistent with recently reported host restrictions in the complement cascade. However, Lst-deficient gonococci were killed more rapidly than sialylated wild-type gonococci following intraperitoneal injection into normal mice, which is consistent with sialylation conferring protection against killing by polymorphonuclear leukocytes (PMNs). As reported for human PMNs, sialylated gonococci were more resistant to killing by murine PMNs, and sialylation led to reduced association with and induction of a weaker respiratory burst in PMNs from estradiol-treated mice. In summary, these studies suggest sialylation confers a survival advantage to N. gonorrhoeae in mice by increasing resistance to PMN killing. This report is the first direct demonstration that alpha-2,3-sialyltransferase contributes to N. gonorrhoeae pathogenesis in an in vivo model. This study also validates the use of experimental murine infection to study certain aspects of gonococcal pathogenesis.