The biology of the gonococcus

Neisseria gonorrhoeae physiology and pathogenesis

Neisseria gonorrhoeae is an obligate human pathogen that is the cause of the sexually transmitted disease gonorrhoea. Recently, there has been a surge in gonorrhoea cases that has been exacerbated by the rapid rise in gonococcal multidrug resistance to all useful antimicrobials resulting in this organism becoming a significant public health burden. Therefore, there is a clear and present need to understand the organism's biology through its physiology and pathogenesis to help develop new intervention strategies. The gonococcus initially colonises and adheres to host mucosal surfaces utilising a type IV pilus that helps with microcolony formation. Other adhesion strategies include the porin, PorB, and the phase variable outer membrane protein Opa. The gonococcus is able to subvert complement mediated killing and opsonisation by sialylation of its lipooligosaccharide and deploys a series of anti-phagocytic mechanisms. N. gonorrhoeae is a fastidious organism that is able to grow on a limited number of primary carbon sources such as glucose and lactate. The utilization of lactate by the gonococcus has been implicated in a number of pathogenicity mechanisms. The bacterium lives mainly in microaerobic environments and can grow both aerobically and anaerobically with the aid of nitrite. The gonococcus does not produce siderophores for scavenging iron but can utilize some produced by other bacteria, and it is able to successful chelate iron from host haem, transferrin and lactoferrin. The gonococcus is an incredibly versatile human pathogen; in the following chapter, we detail the intricate mechanisms used by the bacterium to invade and survive within the host.

Transcriptional and Translational Responsiveness of the Neisseria gonorrhoeae Type IV Secretion System to Conditions of Host Infections

The type IV secretion system of Neisseria gonorrhoeae translocates single-stranded DNA into the extracellular space, facilitating horizontal gene transfer and initiating biofilm formation. Expression of this system has been observed to be low under laboratory conditions, and multiple levels of regulation have been identified. We used a translational fusion of lacZ to traD, the gene for the type IV secretion system coupling protein, to screen for increased type IV secretion system expression. We identified several physiologically relevant conditions, including surface adherence, decreased manganese or iron, and increased zinc or copper, which increase gonococcal type IV secretion system protein levels through transcriptional and/or translational mechanisms. These metal treatments are reminiscent of the conditions in the macrophage phagosome. The ferric uptake regulator, Fur, was found to repress traD transcript levels but to also have a second role, acting to allow TraD protein levels to increase only in the absence of iron. To better understand type IV secretion system regulation during infection, we examined transcriptomic data from active urethral infection samples from five men. The data demonstrated differential expression of 20 of 21 type IV secretion system genes during infection, indicating upregulation of genes necessary for DNA secretion during host infection.

Gonorrhoea

The bacterium Neisseria gonorrhoeae causes the sexually transmitted infection (STI) gonorrhoea, which has an estimated global annual incidence of 86.9 million adults. Gonorrhoea can present as urethritis in men, cervicitis or urethritis in women, and in extragenital sites (pharynx, rectum, conjunctiva and, rarely, systemically) in both sexes. Confirmation of diagnosis requires microscopy of Gram-stained samples, bacterial culture or nucleic acid amplification tests. As no gonococcal vaccine is available, prevention relies on promoting safe sexual behaviours and reducing STI-associated stigma, which hinders timely diagnosis and treatment thereby increasing transmission. Single-dose systemic therapy (usually injectable ceftriaxone plus oral azithromycin) is the recommended first-line treatment. However, a major public health concern globally is that N. gonorrhoeae is evolving high levels of antimicrobial resistance (AMR), which threatens the effectiveness of the available gonorrhoea treatments. Improved global surveillance of the emergence, evolution, fitness, and geographical and temporal spread of AMR in N. gonorrhoeae, and improved understanding of the pharmacokinetics and pharmacodynamics for current and future antimicrobials in the treatment of urogenital and extragenital gonorrhoea, are essential to inform treatment guidelines. Key priorities for gonorrhoea control include strengthening prevention, early diagnosis, and treatment of patients and their partners; decreasing stigma; expanding surveillance of AMR and treatment failures; and promoting responsible antimicrobial use and stewardship. To achieve these goals, the development of rapid and affordable point-of-care diagnostic tests that can simultaneously detect AMR, novel therapeutic antimicrobials and gonococcal vaccine(s) in particular is crucial.

Phenotypic MicroArray Screening of Neisseria gonorrhoeae in Chemically Defined Liquid Medium

Phenotype MicroArrays (PMs) provide a considerable benefit to the evaluation of potential vaccine/drug targets and the assessment of hypothetical protein function. Nearly 2000 conditions can be screened relatively quickly either to search for phenotypes associated with the loss of a protein or to understand metabolic differences between closely related bacterial isolates. The fastidious organism Neisseria gonorrhoeae presents an experimental challenge for phenotypic screening due to its nutrient restrictions and its autolytic activity upon reaching the stationary phase of growth. These limitations can be mitigated by modulating screening parameters. In this chapter, we describe a technique optimized for the phenotypic screening of N. gonorrhoeae FA1090 and isogenic mutant strains. Inoculum size and culturing times have been adjusted for growth in chemically defined, protein-free Graver-Wade liquid medium in the 96-well microtiter plate format employed by the PMs. With the conditions presented, highly reproducible gonococcal growth is achieved, and autolysis prior to the experimental endpoint is minimized.

Proteomics, Bioinformatics and Structure-Function Antigen Mining For Gonorrhea Vaccines

Expanding efforts to develop preventive gonorrhea vaccines is critical because of the serious health consequences combined with the prevalence and the dire possibility of untreatable gonorrhea. Reverse vaccinology, which includes genome and proteome mining, has proven successful in the discovery of vaccine candidates against many pathogenic bacteria. Here, we describe proteomic applications including comprehensive, quantitative proteomic platforms and immunoproteomics coupled with broad-ranging bioinformatics that have been applied for antigen mining to develop gonorrhea vaccine(s). We further focus on outlining the vaccine candidate decision tree, describe the structure-function of novel proteome-derived antigens as well as ways to gain insights into their roles in the cell envelope, and underscore new lessons learned about the fascinating biology of Neisseria gonorrhoeae.

In Vivo-Selected Compensatory Mutations Restore the Fitness Cost of Mosaic penA Alleles That Confer Ceftriaxone Resistance in Neisseria gonorrhoeae

Resistance to ceftriaxone in Neisseria gonorrhoeae is mainly conferred by mosaic penA alleles that encode penicillin-binding protein 2 (PBP2) variants with markedly lower rates of acylation by ceftriaxone. To assess the impact of these mosaic penA alleles on gonococcal fitness, we introduced the mosaic penA alleles from two ceftriaxone-resistant (Cro^r) clinical isolates (H041 and F89) into a Cro^s strain (FA19) by allelic exchange and showed that the resultant Cro^r mutants were significantly outcompeted by the Cro^s parent strain in vitro and in a murine infection model. Four Cro^r compensatory mutants of FA19 penA41 were isolated independently from mice that outcompeted the parent strain both in vitro and in vivo. One of these compensatory mutants (LV41C) displayed a unique growth profile, with rapid log growth followed by a sharp plateau/gradual decline at stationary phase. Genome sequencing of LV41C revealed a mutation (G348D) in the acnB gene encoding the bifunctional aconitate hydratase 2/2 methylisocitrate dehydratase. Introduction of the acnB_G348D allele into FA19 penA41 conferred both a growth profile that phenocopied that of LV41C and a fitness advantage, although not as strongly as that exhibited by the original compensatory mutant, suggesting the existence of additional compensatory mutations. The mutant aconitase appears to be a functional knockout with lower activity and expression than wild-type aconitase. Transcriptome sequencing (RNA-seq) analysis of FA19 penA41 acnB_G348D revealed a large set of upregulated genes involved in carbon and energy metabolism. We conclude that compensatory mutations can be selected in Cro^r gonococcal strains that increase metabolism to ameliorate their fitness deficit.

The emergence of ceftriaxone-resistant (Cro^r) Neisseria gonorrhoeae has led to the looming threat of untreatable gonorrhea. Whether Cro resistance is likely to spread can be predicted from studies that compare the relative fitnesses of susceptible and resistant strains that differ only in the penA gene that confers Cro resistance. We showed that mosaic penA alleles found in Cro^r clinical isolates are outcompeted by the Cro^s parent strain in vitro and in vivo but that compensatory mutations that allow ceftriaxone resistance to be maintained by increasing bacterial fitness are selected during mouse infection. One compensatory mutant that was studied in more detail had a mutation in acnB, which encodes the aconitase that functions in the tricarboxylic acid (TCA) cycle. This study illustrates that compensatory mutations can be selected during infection, which we hypothesize may allow the spread of Cro resistance in nature. This study also provides novel insights into gonococcal metabolism and physiology.

Deciphering the Function of New Gonococcal Vaccine Antigens Using Phenotypic Microarrays

The function and extracellular location of cell envelope proteins make them attractive candidates for developing vaccines against bacterial diseases, including challenging drug-resistant pathogens, such as Neisseria gonorrhoeae A proteomics-driven reverse vaccinology approach has delivered multiple gonorrhea vaccine candidates; however, the biological functions of many of them remain to be elucidated. Herein, the functions of six gonorrhea vaccine candidates-NGO2121, NGO1985, NGO2054, NGO2111, NGO1205, and NGO1344-in cell envelope homeostasis were probed using phenotype microarrays under 1,056 conditions and a ΔbamE mutant (Δngo1780) as a reference of perturbed outer membrane integrity. Optimal growth conditions for an N. gonorrhoeae phenotype microarray assay in defined liquid medium were developed, which can be useful in other applications, including rapid and thorough antimicrobial susceptibility assessment. Our studies revealed 91 conditions having uniquely positive or negative effects on one of the examined mutants. A cluster analysis of 37 and 57 commonly beneficial and detrimental compounds, respectively, revealed three separate phenotype groups: NGO2121 and NGO1985; NGO1344 and BamE; and the trio of NGO1205, NGO2111, and NGO2054, with the last protein forming an independent branch of this cluster. Similar phenotypes were associated with loss of these vaccine candidates in the highly antibiotic-resistant WHO X strain. Based on their extensive sensitivity phenomes, NGO1985 and NGO2121 appear to be the most promising vaccine candidates. This study establishes the principle that phenotype microarrays can be successfully applied to a fastidious bacterial organism, such as N. gonorrhoeae IMPORTANCE Innovative approaches are required to develop vaccines against prevalent and neglected sexually transmitted infections, such as gonorrhea. Herein, we have utilized phenotype microarrays in the first such investigation into Neisseria gonorrhoeae to probe the function of proteome-derived vaccine candidates in cell envelope homeostasis. Information gained from this screening can feed the vaccine candidate decision tree by providing insights into the roles these proteins play in membrane permeability, integrity, and overall N. gonorrhoeae physiology. The optimized screening protocol can be applied in investigations into the function of other hypothetical proteins of N. gonorrhoeae discovered in the expanding number of whole-genome sequences, in addition to revealing phenotypic differences between clinical and laboratory strains.

Antigenic Variation in Bacterial Pathogens

Antigenic variation is a strategy used by a broad diversity of microbial pathogens to persist within the mammalian host. Whereas viruses make use of a minimal proofreading capacity combined with large amounts of progeny to use random mutation for variant generation, antigenically variant bacteria have evolved mechanisms which use a stable genome, which aids in protecting the fitness of the progeny. Here, three well-characterized and highly antigenically variant bacterial pathogens are discussed: Anaplasma, Borrelia, and Neisseria. These three pathogens display a variety of mechanisms used to create the structural and antigenic variation needed for immune escape and long-term persistence. Intrahost antigenic variation is the focus; however, the role of these immune escape mechanisms at the population level is also presented.

Antimicrobial effects of copper(II) bis(thiosemicarbazonato) complexes provide new insight into their biochemical mode of action

The copper(II) complexes of bis-thiosemicarbazones (Cu(btsc)) such as Cu(atsm) and Cu(gtsm) are neutral, lipophilic compounds that show promise as therapeutics for the treatment of certain neurological diseases and cancers. Although the effects of these compounds have been described at the cellular level, there is almost no information about their biochemical mode of action. In this work, we showed that Cu(atsm) and Cu(gtsm) displayed antimicrobial activities against the human obligate pathogen Neisseria gonorrhoeae that were more than 100 times more potent than Cu(NO3)2 salt alone. Treatment with Cu(btsc) also produced phenotypes that were consistent with copper poisoning, but the levels of intracellular copper were undetectable by ICP MS. We observed that Cu(btsc) interacted with proteins in the cell membrane. Systematic measurements of O2 uptake further demonstrated that treatment with both Cu(atsm) and Cu(gtsm) led to dose-dependent inhibition of respiratory electron transfer processes via succinate and NADH dehydrogenases. These dehydrogenases were not inhibited by a non-btsc source of Cu(II). The results led us to conclude that the biochemical mechanism of Cu(btsc) action is likely more complex than the present, simplistic model of copper release into the cytoplasm.

Legless pathogens: how bacterial physiology provides the key to understanding pathogenicity

This review argues that knowledge of microbial physiology and metabolism is a prerequisite to understanding mechanisms of pathogenicity. The ability of Neisseria gonorrhoeae to cope with stresses such as those found during infection requires a sialyltransferase to sialylate its lipopolysaccharide using host-derived CMP-NANA in the human bloodstream, the ability to oxidize lactate that is abundant in the human body, outer-membrane lipoproteins that provide the first line of protection against oxidative and nitrosative stress, regulation of NO reduction independently from the nitrite reductase that forms NO, an extra haem group on the C-terminal extension of a cytochrome oxidase subunit, and a respiratory capacity far in excess of metabolic requirements. These properties are all normal components of neisserial physiology; they would all fail rigid definitions of a pathogenicity determinant. In anaerobic cultures of enteric bacteria, duplicate pathways for nitrate reduction to ammonia provide a selective advantage when nitrate is either abundant or scarce. Selection of these alternative pathways is in part regulated by two parallel two-component regulatory systems. NarX-NarL primarily ensures that nitrate is reduced in preference to thermodynamically less favourable terminal electron acceptors, but NarQ-NarP facilitates reduction of limited quantities of nitrate or other, less favourable, terminal electron acceptors in preference to fermentative growth. How enteric bacteria repair damage caused by nitrosative and oxidative damage inflicted by host defences is less well understood. In both N. gonorrhoeae and Escherichia coli, parallel pathways that duplicate particular biochemical functions are far from redundant, but fulfil specific physiological roles.

Independent evolution of the core and accessory gene sets in the genus Neisseria: insights gained from the genome of Neisseria lactamica isolate 020-06

BACKGROUND

The genus Neisseria contains two important yet very different pathogens, N. meningitidis and N. gonorrhoeae, in addition to non-pathogenic species, of which N. lactamica is the best characterized. Genomic comparisons of these three bacteria will provide insights into the mechanisms and evolution of pathogenesis in this group of organisms, which are applicable to understanding these processes more generally.

RESULTS

Non-pathogenic N. lactamica exhibits very similar population structure and levels of diversity to the meningococcus, whilst gonococci are essentially recent descendents of a single clone. All three species share a common core gene set estimated to comprise around 1190 CDSs, corresponding to about 60% of the genome. However, some of the nucleotide sequence diversity within this core genome is particular to each group, indicating that cross-species recombination is rare in this shared core gene set. Other than the meningococcal cps region, which encodes the polysaccharide capsule, relatively few members of the large accessory gene pool are exclusive to one species group, and cross-species recombination within this accessory genome is frequent.

CONCLUSION

The three Neisseria species groups represent coherent biological and genetic groupings which appear to be maintained by low rates of inter-species horizontal genetic exchange within the core genome. There is extensive evidence for exchange among positively selected genes and the accessory genome and some evidence of hitch-hiking of housekeeping genes with other loci. It is not possible to define a 'pathogenome' for this group of organisms and the disease causing phenotypes are therefore likely to be complex, polygenic, and different among the various disease-associated phenotypes observed.

Assessing the precision of high-throughput computational and laboratory approaches for the genome-wide identification of protein subcellular localization in bacteria

BACKGROUND

Identification of a bacterial protein's subcellular localization (SCL) is important for genome annotation, function prediction and drug or vaccine target identification. Subcellular fractionation techniques combined with recent proteomics technology permits the identification of large numbers of proteins from distinct bacterial compartments. However, the fractionation of a complex structure like the cell into several subcellular compartments is not a trivial task. Contamination from other compartments may occur, and some proteins may reside in multiple localizations. New computational methods have been reported over the past few years that now permit much more accurate, genome-wide analysis of the SCL of protein sequences deduced from genomes. There is a need to compare such computational methods with laboratory proteomics approaches to identify the most effective current approach for genome-wide localization characterization and annotation.

RESULTS

In this study, ten subcellular proteome analyses of bacterial compartments were reviewed. PSORTb version 2.0 was used to computationally predict the localization of proteins reported in these publications, and these computational predictions were then compared to the localizations determined by the proteomics study. By using a combined approach, we were able to identify a number of contaminants and proteins with dual localizations, and were able to more accurately identify membrane subproteomes. Our results allowed us to estimate the precision level of laboratory subproteome studies and we show here that, on average, recent high-precision computational methods such as PSORTb now have a lower error rate than laboratory methods.

CONCLUSION

We have performed the first focused comparison of genome-wide proteomic and computational methods for subcellular localization identification, and show that computational methods have now attained a level of precision that is exceeding that of high-throughput laboratory approaches. We note that analysis of all cellular fractions collectively is required to effectively provide localization information from laboratory studies, and we propose an overall approach to genome-wide subcellular localization characterization that capitalizes on the complementary nature of current laboratory and computational methods.

An NMR and enzyme study of the carbon metabolism of Neisseria meningitidis

The pathogenic neisseriae are fastidious bacteria that are only able to grow on a restricted range of carbon sources. The genome sequence of Neisseria meningitidis strain MC58 predicts the presence of a complete citric acid cycle (CAC), but there have been no detailed biochemical studies of carbon metabolism in this important pathogen. In this study, both NMR and conventional enzyme assays were used to investigate the central metabolic pathways of a serogroup B strain (K454). (13)C-NMR labelling patterns of amino acids from hydrolysed cell proteins after growth with either 2- or 3-[(13)C]pyruvate were consistent with the operation of a complete oxidative CAC. Enzyme assays showed that cell-free extracts contained all the CAC enzymes predicted from the genome sequence, including a membrane-bound malate:quinone oxidoreductase which is present in place of the conventional NAD-linked cytoplasmic malate dehydrogenase. (1)H-NMR studies showed that growth on glucose, lactate and, especially, pyruvate, resulted in the excretion of significant amounts of acetate into the culture supernatant. This occurred via the phosphotransacetylase (PTA)-acetate kinase (ACK) pathway. Extremely high specific activities of PTA (7-14 micromol min(-1) mg(-1)) were detected in cell-free extracts, although ACK activities were much lower (46-298 nmol min(-1) mg(-1)). Expression of PTA and ACK activities was not co-ordinately regulated during growth on combinations of carbon sources. This may be related to the presence of two ackA paralogues in N. meningitidis which are, unusually, unlinked to the pta gene.

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.

Neisseria gonorrhoeae possesses two nicotinamide adenine dinucleotide-independent lactate dehydrogenases

An important metabolic capability of Neisseria gonorrhoeae is the utilization of host-derived lactate. Two isoenzymes of the membrane-associated, pyridine dinucleotide-independent type of lactate dehydrogenase (iLDH) participate in lactate assimilation, but exhibit distinctive properties. Isoenzyme iLDH-I utilized lactate exclusively as substrate, exhibiting a preference for the D-isomer. In contrast, isoenzyme iLDH-II exhibited broad substrate specificity (lactate, phenyllactate, and 4-hydroxyphenyllactate), but was stereospecific for the L-isomers. These results explain the difficulty in isolating mutants unable to utilize lactate.

Metabolic responses of Neisseria gonorrhoeae to human serum and myeloid cells. Adaptation to host defenses?

The interaction of gonococci with host defenses including serum and phagocytic cells has been extensively studied. We have shown that a small molecular weight factor in serum stimulates gonococcal metabolism. This factor has now been isolated by column chromatography and may be released from mammalian cells including phagocytes. Exposure of gonococci to serum decreases membrane fluidity as demonstrated by EPR, seems to reduce OMP shedding, and reduces uptake by PMNS. Serum stimulated gonococci consume O2 to an extent adequate to interfere with PMN formation of reactive oxygen intermediates. We propose that all of these responses are adaptive and favor survival of this pathogen.

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

Growth of Neisseria gonorrhoeae strain FA171 in continuous culture under glucose-limiting conditions resulted in a growth-rate-dependent change in the lipopolysaccharide (LPS). The evidence for this change is an alteration in the mobility of purified alkali-treated LPS on sodium dodecyl sulfate-polyacrylamide gels and a quantitative difference in the amount of the LPS serotype antigen. The LPS from cells grown at a low dilution rate (0.12 h-1) contained ca. eightfold less serotype antigen than the LPS from cells grown at a high dilution rate (0.56 h-1). The decrease in LPS serotype antigen was associated with an increase in sensitivity to the bactericidal activity of normal human serum and an increase in cell surface hydrophobicity. An increase in the amount of serotype antigen was associated with a reduction in the accessibility of a monoclonal antibody to a core LPS determinant, an increase in resistance to normal human serum, and a decrease in cell surface hydrophobicity. The microheterogeneity of gonococcal LPS with respect to the content of serotype antigen may result from an alteration in the metabolism of glucose.

Interaction of Escherichia coli with different fimbriae and polymorphonuclear leukocytes

The effects of Escherichia coli strains with various fimbriae on bacteria-polymorphonuclear leukocyte (PMN) interactions were studied. Strains of E. coli were cultivated at 37 degrees C to express and at 18 degrees C to suppress the formation of fimbriae. The presence of fimbriae was confirmed by electron microscopic studies and hemagglutination and salt aggregation tests. Fimbriated E. coli strains were more readily PMN associated than the nonfimbriated strains in the absence of opsonins, confirming the results of previous studies. However, the PMN chemiluminescence (CL) induced by the various strains in the absence of serum opsonins depended on the type of fimbriae they expressed. Strains with type 1 fimbriae expressing mannose-sensitive hemagglutination induced 5 to 15 times more CL than the same strains grown at 18 degrees C, i.e., not expressing this type of fimbriae. For strains showing mannose-resistant hemagglutination, the differences between fimbriated and nonfimbriated variants of the same strains grown at 37 and 18 degrees C, respectively, were less pronounced. Analysis of enterotoxigenic strains expressing colonization factor antigen I (CFA/I) fimbriae showed that these induced only 25 to 33% of the CL induced by the same E. coli strains not expressing CFA/I, whereas enterotoxigenic strains expressing CFA/II fimbriae induced 100 to 200% of the CL induced by the nonfimbriated variants. Although less CL was induced by bacteria with CFA/I fimbriae than by nonfimbriated variants, this situation was reversed when the microorganisms were opsonized. Thus, CFA/I fimbriae, while enhancing adhesion to cells, induce less activation of PMN-killing mechanisms in a serum-free environment. These findings may be relevant for the virulence in certain body sites, since CFA/I fimbriae, while facilitating adhesiveness, may protect the bacteria from PMN killing. Our findings indicate that PMN interactions with fimbriated E. coli in the host defense may be complex. Certain fimbriae may indeed be advantageous to the bacteria, enabling them to interact with PMNs without activating the bactericidal oxidative metabolism.

Neisseria gonorrhoeae cell envelope: permeability to hydrophobic molecules

Isogenic variants of antibiotic-resistant and -sensitive Neisseria gonorrhoeae were examined for differences in the inhibition of oxygen uptake by steroid hormones. Mutants designated as env, which possessed cell envelope mutations allowing phenotypic suppression of low-level antibiotic resistance, were more sensitive to steroid hormone inhibition of oxygen uptake than the wild-type parental strains. Possession of an mtr locus, which confers nonspecific resistance to multiple antibiotics, dyes, and detergents, was also associated with an increase in resistance to steroid hormone inhibition of oxygen uptake. The penA2 locus, which confers an eightfold increase in resistance to penicillin, was not responsible for the increased resistance to steroid hormones. Phospholipids in the outer membrane of intact env-2 cells were susceptible to digestion by phospholipase C, indicating exposure of phospholipid head groups on the outer surface. Cells of a wild-type and mtr-2 strain were not susceptible to phospholipase C digestion unless they were pretreated with mixed exoglycosidases. This pretreatment also increased the sensitivity of mtr-2 cells to progesterone inhibition of O2 uptake. These data suggest that the permeability of the gonococcus to hydrophobic antibiotic and steroid molecules is mediated by the degree of phospholipid exposure on the outer membrane.

L-cysteine oxidase activity in the membrane of Neisseria meningitidis

Among the L-amino acids, only L-cysteine was oxidized by isolated washed membranes of group B Neisseria meningitidis SD1C. The cysteine oxidase in the membrane obeyed Michaelis-Menten kinetics and was heat labile. The pH optimum for the maximum velocity of the reaction was 9.8. Specific activity of the enzyme increased as cell growth progressed through the exponential phase toward the stationary phase of growth. The enzyme activity was markedly sensitive to inhibition by metal chelators, but was resistant to inhibitors of terminal oxidases with the exception of cyanide. All known cytochromes in the membrane, except b563, were reduced with L-cysteine. The additive nature of L-cysteine oxidase and succinate oxidase activities suggests that an unidentified oxidase is involved in the oxidation of cysteine.

Pyocin inhibition of Neisseria gonorrhoeae: mechanism of action

Purified R-type pyocins (611 131) from Pseudomonas aeruginosa PA103 exhibited bactericidal activity against Neisseria gonorrhoeae. Killing of gonococci was a single-hit process requiring as few as 1 pyocin per colony-forming unit. Deoxyriboinucleic acid, ribonucleic acid, protein, and lipid syntheses were rapidly and completely inhibited. Oxygen uptake was also inhibited, but occurred after the inhibition of macromolecular synthesis. The cell lysis which occurred after pyocin inhibition of gonococcal growth was the result of endogenous gonococcal autolysin activity.

Cytoplasmic membrane proteins of spectinomycin-susceptible and -resistant strains of Neisseria gonorrhoeae

Cytoplasmic membranes were isolated and examined from two spectinomycin-susceptible and three spectinomycin-resistant clinical strains of Neisseria gonorrhoeae. A laboratory-derived spectinomycin-resistant mutant, obtained by serial passage on gradually increasing concentrations of the antibiotic, and a susceptible revertant, spontaneously arising from one of the resistant clinical strains, were also studied. Sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis revealed that a major protein, comprising about 7% of total cytoplasmic membrane protein (molecular weight 24,000), was absent in the three clinically isolated spectinomycin-resistant strains. In a revertant, this protein reappeared. During treatment of one of the susceptible strains with spectinomycin, the protein disappeared. However, this correlation was not maintained in the laboratory-derived spectinomycin-resistant mutant. This mutant was of comparable resistant to the clinical isolates, but the 24,000-molecular-weight protein was present in normal quantities. In addition, spectinomycin resistant in clinical isolates was variable compared with stable resistance exhibited by the laboratory-derived mutant. These findings suggested that differences in laboratory-derived versus clinical spectinomycin resistance may be due to different types of resistance mutations.

Terminal branching of the respiratory electron transport chain in Neisseria meningitidis

The respiratory components of the envelope membrane preparation of Neisseria meningitidis were investigated. Oxidase activities were demonstrated in this fraction in the presence of succinic acid, reduced nicotinamide adenine dinucleotide, and ascorbate-N,N,N',N'-tetramethyl-p-phenylene-diamine (TMPD). Differences in the kinetics of inhibition by terminal oxidase inhibitors on the three oxidase activities indicated that ascorbate-TMPD oxidation involved only an azide-sensitive oxidase, whereas oxidation of the physiological substrates involved two oxidases, one of which was relatively azide resistant. Spectrophotometric studies revealed that ascorbate-TMPD donated its electrons exclusively to cytochrome o, whereas the physiological substrates were oxidized via both cytochromes o and a. The effects of class II inhibitors on the oxidases suggest terminal branching of the electron transport chain at the cytochrome b level. A model of the respiratory system in N. meningitidis is proposed.