Penicillin sensitivity and serum resistance are independent attributes of strains of Neisseria gonorrhoeae causing disseminated gonococcal infection

Neisseria gonorrhoeae Aggregation Reduces Its Ceftriaxone Susceptibility

Antibiotic resistance in Neisseria gonorrhoeae (GC) has become an emerging threat worldwide and heightens the need for monitoring treatment failures. N. gonorrhoeae, a gram-negative bacterium responsible for gonorrhea, infects humans exclusively and can form aggregates during infection. While minimal inhibitory concentration (MIC) tests are often used for determining antibiotic resistance development and treatment, the knowledge of the true MIC in individual patients and how it relates to this laboratory measure is not known. We examined the effect of aggregation on GC antibiotic susceptibility and the relationship between bacterial aggregate size and their antibiotic susceptibility. Aggregated GC have a higher survival rate when treated with ceftriaxone than non-aggregated GC, with bacteria in the core of the aggregates surviving the treatment. GC lacking opacity-associated protein or pili, or expressing a truncated lipooligosaccharide, three surface molecules that mediate GC-GC interactions, reduce both aggregation and ceftriaxone survival. This study demonstrates that the aggregation of N. gonorrhoeae can reduce the susceptibility to antibiotics, and suggests that antibiotic utilization can select for GC surface molecules that promote aggregation which in turn drive pathogen evolution. Inhibiting aggregation may be a potential way of increasing the efficacy of ceftriaxone treatment, consequently reducing treatment failure.

Gonorrhea - an evolving disease of the new millennium

Etiology, transmission and protection: Neisseria gonorrhoeae (the gonococcus) is the etiological agent for the strictly human sexually transmitted disease gonorrhea. Infections lead to limited immunity, therefore individuals can become repeatedly infected. Pathology/symptomatology: Gonorrhea is generally a non-complicated mucosal infection with a pustular discharge. More severe sequellae include salpingitis and pelvic inflammatory disease which may lead to sterility and/or ectopic pregnancy. Occasionally, the organism can disseminate as a bloodstream infection. Epidemiology, incidence and prevalence: Gonorrhea is a global disease infecting approximately 60 million people annually. In the United States there are approximately 300, 000 cases each year, with an incidence of approximately 100 cases per 100,000 population. Treatment and curability: Gonorrhea is susceptible to an array of antibiotics. Antibiotic resistance is becoming a major problem and there are fears that the gonococcus will become the next "superbug" as the antibiotic arsenal diminishes. Currently, third generation extended-spectrum cephalosporins are being prescribed. Molecular mechanisms of infection: Gonococci elaborate numerous strategies to thwart the immune system. The organism engages in extensive phase (on/off switching) and antigenic variation of several surface antigens. The organism expresses IgA protease which cleaves mucosal antibody. The organism can become serum resistant due to its ability to sialylate lipooligosaccharide in conjunction with its ability to subvert complement activation. The gonococcus can survive within neutrophils as well as in several other lymphocytic cells. The organism manipulates the immune response such that no immune memory is generated which leads to a lack of protective immunity.

Phase variable changes in genes lgtA and lgtC within the lgtABCDE operon of Neisseria gonorrhoeae can modulate gonococcal susceptibility to normal human serum

The α-chain of the core oligosaccharide of the lipo-oligosaccharide (LOS) produced by Neisseria gonorrhoeae can undergo reversible and rapid changes in structure due to phase-variable production of certain enzymes employed in the biosynthesis of the lacto- N-neotetraose structure. Five of these enzymes are encoded by the lgtABCDE operon, and polynucleotide tracts within three of these genes ( lgtA, lgtC and lgtD) can be substrates for slipped-strand mispairing events that lead to nucleotide insertions or deletion events which result in variable production of their respective gene products. We now report that phase-variable synthesis of the lgtA and lgtC gene products in strain FA19 results in the production of elongated LOS α-chains and that the presence of these LOS species can result in gonococci being sensitive to the bacteriolytic action of serum-antibody and complement. Hence, phase variation within the lgtABCDE operon can significantly impact the ability of gonococci to subvert this important host defense system.

Species status of Neisseria gonorrhoeae: evolutionary and epidemiological inferences from multilocus sequence typing

Background

Various typing methods have been developed for Neisseria gonorrhoeae, but none provide the combination of discrimination, reproducibility, portability, and genetic inference that allows the analysis of all aspects of the epidemiology of this pathogen from a single data set. Multilocus sequence typing (MLST) has been used successfully to characterize the related organisms Neisseria meningitidis and Neisseria lactamica. Here, the same seven locus Neisseria scheme was used to characterize a diverse collection of N. gonorrhoeae isolates to investigate whether this method would allow differentiation among isolates, and to distinguish these three species.

Results

A total of 149 gonococcal isolates were typed and submitted to the Neisseria MLST database. Although relatively few (27) polymorphisms were detected among the seven MLST loci, a total of 66 unique allele combinations (sequence types, STs), were observed, a number comparable to that seen among isolate collections of the more diverse meningococcus. Patterns of genetic variation were consistent with high levels of recombination generating this diversity. There was no evidence for geographical structuring among the isolates examined, with isolates collected in Liverpool, UK, showing levels of diversity similar to a global collection of isolates. There was, however, evidence that populations of N. meningitidis, N. gonorrhoeae and N. lactamica were distinct, with little support for frequent genetic recombination among these species, with the sequences from the gdh locus alone grouping the species into distinct clusters.

Conclusion

The seven loci Neisseria MLST scheme was readily adapted to N. gonorrhoeae isolates, providing a highly discriminatory typing method. In addition, these data permitted phylogenetic and population genetic inferences to be made, including direct comparisons with N. meningitidis and N. lactamica. Examination of these data demonstrated that alleles were rarely shared among the three species. Analysis of variation at a single locus, gdh, provided a rapid means of identifying misclassified isolates and determining whether mixed cultures were present.

Gonococcal infections in neonates and young children

Gonorrhea has been recognized since antiquity, and more than 60 million new cases occur yearly worldwide. Much has been learned about the molecular pathogenesis of infection by Neisseria gonorrhoeae, but immunity from natural infection does not protect against reinfection with the same strain, and the goal of a protective vaccine remains elusive. Gonococcal ophthalmia neonatorum is the most common manifestation in infants born to mothers with gonococcal genital tract infections. Genital and pharyngeal gonococcal infections in young children almost always are acquired from sexual abuse by an infected adult. Invasive disease can occur at any age but is uncommon. Nonculture diagnostic tests are widely used in adults, but culture is required in children for medicolegal purposes. N. gonorrhoeae strains have developed resistance to many antibiotic classes, and resistance profiles vary among geographic regions and within regions over time. Current guidelines for treatment of gonococcal infections in children in the United States are reviewed.

A variable genetic island specific for Neisseria gonorrhoeae is involved in providing DNA for natural transformation and is found more often in disseminated infection isolates

Neisseria gonorrhoeae (the gonococcus) is the causative agent of the sexually transmitted disease gonorrhoea. Most gonococcal infections remain localized to the genital tract but, in a small proportion of untreated cases, the bacterium becomes systemic to produce the serious complication of disseminated gonococcal infection (DGI). We have identified a large region of chromosomal DNA in N. gonorrhoeae that is not found in a subset of gonococcal isolates (a genetic island), in the closely related pathogen, Neisseria meningitidis or in commensal Neisseria that do not usually cause disease. Certain versions of the island carry a serum resistance locus and a gene for the production of a cytotoxin; these versions of the island are found preferentially in DGI isolates. All versions of the genetic island encode homologues of F factor conjugation proteins, suggesting that, like some other pathogenicity islands, this region encodes a conjugation-like secretion system. Consistent with this hypothesis, a wild-type strain released large amounts of DNA into the medium during exponential growth without cell lysis, whereas an isogenic strain mutated in a peptidoglycan hydrolase gene (atlA) was drastically reduced in its ability to donate DNA for transformation during growth. This genetic island constitutes the first major discriminating factor between the gonococcus and the other Neisseria and carries genes for providing DNA for genetic transformation.

Arginine-, hypoxanthine-, uracil-requiring isolates of Neisseria gonorrhoeae are a clonal lineage with a non-clonal population

Multilocus enzyme electrophoresis has shown that a collection of 101 arginine-, hypoxanthine-, uracil-requiring (AHU-) isolates of Neisseria gonorrhoeae, recovered over a 39 year period from the UK and Denmark, were of a single electrophoretic type (91% of strains), or differed from the predominant electrophoretic type at only a single locus. The striking uniformity of the AHU-isolates, and the correlation between auxotype, serovar and overall genetic background, contrasts with previous studies of gonococcal populations (that included very few AHU-strains), and a small sample of non-AHU-isolates studied here, which demonstrated a non-clonal population structure and a lack of association between auxotype, serovar and genetic background. There was no marked difference in the ability of AHU-isolates to be transformed with their own DNA, or with DNA from gonococci of other auxotypes, and the relative genetic stability of AHU-isolates does not appear to be due to a defect in their ability to be transformed. An alternative possibility is that AHU-gonococci recombine with other lineages, but that the resulting recombinants are not maintained in the population. This would occur, for example, if AHU-gonococci competed poorly in mixed infections, within which effective recombination between lineages occurs, and are usually only transmitted from individuals who are singly infected with an AHU-strain. The association between AHU-gonococci and asymptomatic infections may lead to an increased rate of transmission of these strains which under this scenario would be needed to prevent them from being lost from the population.

Antigenic variation in Neisseria gonorrhoeae: production of multiple lipooligosaccharides

Individual cells of Neisseria gonorrhoeae may express a single lipooligosaccharide (LOS) component on their cell surfaces, or they may simultaneously express multiple LOS structures. Strain FA19 expresses LOS components that react with monoclonal antibodies (MAbs) 2-1-L8 and 1B2. The genetic locus responsible for this phenotype in FA19 was identified by isolating a clone that is able to impart the ability to simultaneously express both LOS molecules to strain 1291, a strain expressing only the MAb 1B2-reactive LOS. This clone, pCLB1, was characterized, and the gene responsible for the expression of both LOS components was determined to be lsi2. DNA sequence analysis of lsi2(Fa19) indicates that there are several differences between the DNA sequences of lsi2(FA19) and lsi2(1291). The region responsible for the LOS-specific phenotype change in lsi2(FA19) was identified by deletion and transformation analysis, mapping to a polyguanine tract within lsi2 where lsi2(FA19) possesses a +2 frameshift relative to lsi2(1291). The polyguanine tract in lsi2(FA19) was modified by site-directed mutagenesis to change the sequence to GGGAGGTGGCGGA to prevent frameshifting during DNA replication, transcription, and/or translation. Transformants of strain 1291 containing this DNA sequence express a single MAb 2-1-L8-reactive LOS component, the same phenotype exhibited by lsi2-defective strains. These data indicate that FA19 is able to generate a small amount of functional Lsi2 protein via transcriptional and/or translational frameshifting, and this limited amount of protein allows for the expression of MAb 1B2-reactive LOS molecules.

Generation of antiserum to specific epitopes

The ability to prevent disease by immunization with subunit vaccines that incorporate specific epitopes was demonstrated by DiMarchi et al. (1), who used a synthetic peptide to protect cattle against foot-and-mouth disease. However, generation of antibody to peptide antigens is often difficult owing to the small molecular mass and limited chemical complexity. We tested the hypothesis that recombinant DNA and synthetic peptide techniques would make it possible to stimulate vigorous immune responses to specific epitopes of an outer membrane protein of Neisseria gonorrhoeae. The MtrC AP1 sequence from the invariant MtrC gonococcal lipoprotein was genetically fused to maltose binding protein. The resultant fusion protein was used as the primary immunogen to stimulate MtrC AP1-specific antiserum. To enhance antibody production specific to MtrC AP1, boosting immunizations were performed with synthetic MtrC AP1 sequence contained in a multiple antigenic peptide system immunogen. The MtrC AP1-specific antiserum strongly recognized the MtrC protein on Western blots and appeared to bind native MtrC protein in situ. The generation of antibody in this fashion provides the technology to produce antibody to defined epitopes of any protein, including those found in the gonococcal outer membrane. The ability of those antibodies to inhibit bacterial growth or to activate complement protein can then be tested.

Strain characteristics and antibiotic susceptibility of isolates of Neisseria gonorrhoeae causing disseminated gonococcal infection in Australia. Members of the Australian Gonococcal Surveillance Programme

The auxotype (A) and serovar (S) distribution and antibiotic and serum sensitivity of 22 strains of Neisseria gonorrhoeae isolated from blood and joints were determined. With one exception, these strains from disseminated gonococcal infections (DGI) belonged to one of 4 serovars of the IA serogroup and were resistant to killing by normal human serum. The auxotype distribution of these Australian strains differed significantly from that reported elsewhere in that 17 of the 22 isolates were proline requires, but none were of the AHU auxotype. This lack of the AHU auxotype in the DGI strains in Australia was explained by the virtual absence of AHU requirers in a sample of 1560 mucosal strains isolated in Sydney and Darwin from 1987 to 1990. The A/S distribution of these mucosal isolates also helped to account for the low (0.12) percentage of DGI strains in isolates examined by the Australian Gonococcal Surveillance Programme (AGSP) from 1981 to 1991, and the differences in the rates of DGI in Sydney (0.08%) and Darwin (0.87%). There was a relative lack of the IA serogroup strains which are mostly responsible for DGI in the mucosal isolates from Sydney (15% of all strains) but a higher proportion of these serovars (40%) in the Darwin sample. There were 46 cases of DGI in data from the AGSP, 29 of these being women. Seven of the cases diagnosed in Australia were infected with penicillinase-producing gonococci suggesting that antibiotics other than the penicillins should now be used for this condition in this region.

The interaction of naturally elaborated blebs from serum-susceptible and serum-resistant strains of Neisseria gonorrhoeae with normal human serum

We studied the interaction of normal human serum immunoglobulins with outer-membrane bleb antigens of Neisseria gonorrhoeae. Gonococcal 68,000 Dalton and Lip (H.8 antigen) outer-membrane proteins were recognized by normal human serum immunoglobulins in blebs from serum-resistant strains, but not in blebs from serum-susceptible strains. The addition of blebs from a serum-resistant strain to bactericidal assays resulted in significantly greater inhibition of serum killing than the addition of blebs from a serum-susceptible strain. Our results indicate that blebs from two serum-resistant gonococcal strains have an enhanced ability to bind and remove cell-targeted bactericidal factors, and that outer-membrane blebbing may contribute to serum resistance.

Characterization of naturally elaborated blebs from serum-susceptible and serum-resistant strains of Neisseria gonorrhoeae

Outer-membrane blebs from two serum-susceptible and two serum-resistant strains of Neisseria gonorrhoeae were characterized. In general, bleb surfaces resembled cell surfaces, but there were qualitative and quantitative protein differences in blebs released by serum-susceptible and serum-resistant strains. Relative to blebs from serum-resistant strains, blebs from serum-susceptible strains expressed reduced amounts of major outer-membrane proteins I and III, and little if any 68,000 Dalton outer-membrane protein.

Molecular characterization of the argJ mutation in Neisseria gonorrhoeae strains with requirements for arginine, hypoxanthine, and uracil

Arginine auxotrophs are commonly encountered among clinical isolates of Neisseria gonorrhoeae. Arginine auxotrophs which also require hypoxanthine and uracil (AHU strains) compose a unique set of strains that are highly homogeneous and are believed to be clonally derived. The Arg- phenotype of these strains is due to a lesion in the argJ gene encoding ornithine acetyltransferase. We have cloned the mutant argJ gene from an AHU strain and compared the sequence of this gene to the wild-type argJ gene. The mutant gene contained a 3-bp deletion within a repetitive region of the argJ gene. This mutation was restored to the wild-type sequence in a naturally occurring Arg+ revertant of the AHU strain. This deletion was detected in a wide variety of other AHU strains but not in other ArgJ- strains or in ArgJ+ strains, supporting the theory that AHU strains are clonally derived.

Binding of S protein by Neisseria gonorrhoeae and potential role in invasion

An agglutination assay was used to examine the binding of purified human S protein (vitronectin, serum spreading factor) to 201 clinical isolates of Neisseria gonorrhoeae. Strains belonging to the protein IA serovars were significantly (P less than 0.001) more reactive in agglutination tests with human S protein and were more serum resistant than strains belonging to the protein IB serovars. The strains from patients with disseminated infections belonged predominantly to the IA serovar (19 of 23) and, with the exception of IA-4 and certain IB serovars, avidly agglutinated with S protein. The serovar IA-4 and IB strains isolated from joint or cerebrospinal fluid failed to agglutinate with S protein and appeared to be less serum resistant than most other IA isolates. Cysteine hydrochloride or 2-mercaptoethanol inhibited agglutination of S protein and a more than twofold increase in resistance to killing by fresh human serum following preincubation with S protein; the serum-sensitive parent strain did not agglutinate S protein, and serum resistance was not increased following preincubation with this protein. Binding of S protein by gonococci may represent a novel pathogenic mechanism that can contribute to serum resistance.

Characterization of fourteen strains of Neisseria gonorrhoeae: structural analyses and serum reactivities

Resistance to normal human serum (NHS) killing in Neisseria gonorrhoeae has been associated with particular types of Protein I (PI) and lipopolysaccharide (LPS), but many exceptions exist, and the role of these structures in determining serum reactivities remains controversial. In reality, the response of the gonococcus to NHS is probably governed by several parameters involving a number of outer-membrane (OM) components. We surveyed the serum reactivities of 14 strains of N. gonorrhoeae and characterized each of their major OM components. The strains presented a spectrum of sensitivity to pooled NHS. As assessed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, immunoblotting, and peptide mapping, the strains were also quite heterogeneous in terms of PI, H.8 antigen, and LPS type, and the presence of the 2-1-L8 epitope. Five of the strains had identical PIAs in varying LPS and H.8 backgrounds, and four had identical PIBs in varying LPS and H.8 backgrounds. As assessed by electrophoretic migration and monoclonal antibody binding, Protein III and the 44,000 Dalton protein were identical in these strains. We found no association between PI subclass and serum sensitivity, while H.8 and LPS variation appeared to be related to bactericidal responses. The diversity and close interaction of gonococcal components in the OM are undoubtedly involved in differential abilities to survive NHS killing.

Comparison of two serum bactericidal assays for Neisseria gonorrhoeae

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

Phenotypic characteristics of Branhamella catarrhalis strains

Isolates of Branhamella catarrhalis from 13 patients with pneumonia, 6 patients with tracheobronchitis, and 8 patients who were colonized with the organism were studied with respect to susceptibility to the bactericidal action of normal human serum (NHS), glass slide hemagglutination (HA) of group O human erythrocytes, beta-lactamase production, and susceptibility to selected antimicrobial agents and laboratory drugs. A total of 18 of 27 isolates were serum resistant, 22 of 27 produced HA, and 21 of 27 were beta-lactamase positive. Statistically significant correlations were found between susceptibility to NHS and susceptibility to trypsin (r = +0.47; P = 0.01) and between susceptibility to NHS and HA (r = -0.48; P = 0.009). Significant correlations were also observed among several pairs of antimicrobial drugs. Analysis of variance showed that mean ampicillin MICs correlated with isolate group (r = -0.49; P = 0.03) in that the pneumonia isolates had higher MICs. Some phenotypic characteristics appeared to be independent of each other. These data suggest that important differences exist among clinically significant B. catarrhalis strains and that these differences may be due to differences in the cell wall envelope of the organism.

Serum susceptibility of bovine pasteurellas

In this study, the serum sensitivity of 23 P. haemolytica isolates and 18 P. multocida isolates was determined by incubating dilutions of bacteria with equal volumes of fresh or heat-inactivated bovine serum for one, two, or three hours. Clinical isolates of both Pasteurella species were resistant to serum, whereas isolates from asymptomatic cattle varied in serum susceptibility. The classical pathway of complement appeared to be the principal means of complement mediated killing as detected by incubation in the presence or absence of EGTA-MgCl2. Lyzozyme and iron saturation of serum did not greatly affect serum susceptibility with either of the Pasteurella species.

Protein I serotype of serum-resistant versus serum-sensitive Neisseria gonorrhoeae strains

In order to characterize serum-resistant and serum-sensitive strains of N. gonorrhoeae, the protein I serotype, auxotype, and penicillin susceptibility of 128 strains were tested. Sensitivity to the complement-dependent bactericidal activity of normal human serum was highly associated with protein I serotype (p less than 0.001). Thus 85% of serotype 1-3 strains were serum-resistant, whereas 86% of serotype 8 strains and all strains with serotypes 8 + 9 or 9 were serum-sensitive. Serum-resistance or sensitivity for a given serotype was independent of auxotype. The susceptibility to penicillin within the serotypes 1-3 was significantly associated with auxotype (p = 0.0016); all AHU- (requirement for arginine, hypoxanthine and uracil) strains had MICs of penicillin of 0.04 microgram/ml or less and were serotypes 1-3. Among the non-AHU-strains, serotype 9 was significantly more penicillin susceptible than the other serotypes (p less than 0.003).

Epidemiological analysis of Neisseria gonorrhoeae in the Federal Republic of Germany by auxotyping and serological classification using monoclonal antibodies

We evaluated a new serological classification system for Neisseria gonorrhoeae based on monoclonal antibodies directed against epitopes on the outer membrane protein I, in conjunction with auxotyping, to analyse gonococci from two cities in the Federal Republic of Germany. Isolates of N gonorrhoeae were collected during 1976-8 and 1980-2 in Lübeck, and during 1980-2 in Heidelberg. Between the two study periods in Lübeck, we observed an appreciable decrease in strains of the auxotype that requires arginine, hypoxanthine, and uracil (AHU-) and with serovar class PrIA-1 and the emergence of strains with the proline requiring auxotype and PrIB-1 serovar class. Serovar PrIA-1 accounted for 89 (97%) of 92 strains with the AHU- auxotype as opposed to 12 (4%) of 297 strains with other auxotypes (p less than 0.0001). Disseminated gonococcal infection was associated with AHU-/PrIA-1 strains. Penicillinase producing N gonorrhoeae (PPNG) strains belonged to eight different auxotype and serovar classes, which indicated that different strains had been imported. Classification of strains of N gonorrhoeae by auxotype and serovar class permits analysis of temporal changes in gonococcal populations, and of migrations of gonococci between different geographical areas. Typing N gonorrhoeae, together with assessing antibiotic susceptibilities, may prove useful for further studies of the epidemiology and control of gonorrhoea.

Gonococcal endocarditis: a case series demonstrating modern presentation of an old disease

Gonococcal endocarditis appeared with striking frequency in the preantibiotic era compared with its surprising rarity today. We present a series of four episodes of gonococcal endocarditis, which presented to our institution in the last 2 years, after no cases in the previous decade. Three episodes involved the aortic valve and required emergency aortic valve replacement. One episode involved the tricuspid valve and was successfully cured with antibiotic infusion alone. Combining our four patients with the available 25 well-documented gonococcal endocarditis cases reported in the English medical literature during the antibiotic era, we demonstrated that the disease incidence may be increasing, that infections more often involve left-sided cardiac structures (particularly the aortic valve), and that the association with a quotidian fever curve, rash and arthritis, and overt gonococcal infection is less common than previously reported. These patients frequently present with fulminant and dramatic valvular insufficiency without immediately positive blood cultures and complete echocardiographic evaluation seems to provide a valuable aid in making a presumptive diagnosis of endocarditis and directing appropriate clinical management.

Characterization of Neisseria gonorrhoeae protein II phase variation by use of monoclonal antibodies

The protein II (P.II) outer membrane proteins of Neisseria gonorrhoeae, which have been implicated in gonococcal pathogenesis, have been previously shown to undergo a type of phase variation in which expression of any of several different forms of the proteins may be switched on or off. We identified six electrophoretically distinct forms of P.II proteins (designated P.IIa through P.IIf) within strain FA1090, and we isolated colonial variants of FA1090 that expressed only one of the six different P.II protein forms. Two monoclonal antibodies that bound specifically and differentially to P.II proteins were produced. One antibody bound to proteins P.IIb and P.IId and was bactericidal for all colonial variants expressing P.IIb. The second antibody bound to P.IIa and was bactericidal for colonial variants expressing P.IIa. P.II protein profiles of survivors of antibody killing indicated that multiple P.II protein species may be expressed on a single bacterium and that P.II protein switching in the gonococcus is nonrandom.

Monoclonal antibody that recognizes an outer membrane antigen common to the pathogenic Neisseria species but not to most nonpathogenic Neisseria species

A hybridoma derived from a mouse immunized with gonococcal outer membranes produced an antibody, designated H.8, that bound to all strains of Neisseria gonorrhoeae and N. meningitidis tested, and to N. lactamica and N. cinerea, but only rarely to other nonpathogenic Neisseria species. Studies with the gonococcal strain used in production of the antibody showed that the antibody bound to a surface-exposed, protease-sensitive, and heat-modifiable outer membrane antigen that we believe is distinct from previously described gonococcal outer membrane proteins.

Confirmation of association of protein I serotype of Neisseria gonorrhoeae with ability to cause disseminated infection

Previous work indicates that strains of Neisseria gonorrhoeae isolated in Seattle, Wash., and Atlanta, Ga., show an association between serotypes 1 and 2 of protein I of the outer membrane and the ability to cause disseminated infection (T.M. Buchanan and J.F. Hildebrandt, Infect. Immun. 32:985-994, 1981). By using the same serotyping system, we confirmed the association between those serotypes and both disseminated infection and serum resistance in strains from North Carolina. Some strains of the same serotype had protein I species with different apparent molecular weights.

Bactericidal and bacteriolytic activity of serum against gram-negative bacteria

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Dissemination of gonococcal infection is associated with delayed stimulation of complement-dependent neutrophil chemotaxis in vitro

Gonococci isolated from patients with uncomplicated gonorrhea or disseminated infection were examined for their ability to stimulate neutrophil chemotaxis in vitro. A neutrophil chemotactic response was not observed when as many as 10(9) colony-forming units of gonococci were incubated in buffer alone. However, a striking response was observed when 4 x 10(7) colony-forming units were incubated in 10% pooled normal human serum. Activation of complement was required for chemotaxis as demonstrated by complement consumption and failure of chemotactic activity generation in serum treated with heat or EDTA. Chromatography of activated serum demonstrated a single peak of chemotactic activity with an apparent molecular weight of 15,000 and was shown to be due to C5a. Examination of the kinetics of chemotactic factor generation demonstrated that local isolates stimulated a rapid response (about 60% maximal in 5 min), whereas the response to disseminated isolates was delayed (50% maximal in 20 to 30 min). Chemotactic activity generated by both types of isolates was suppressed at early time periods in agammaglobulinemic serum, indicating that immunoglobulins contribute to the generation of activity. Both pathways of complement activation were utilized by the two types of gonococci, but there was preferential dependence on the alternative pathway for disseminated strains and on the classical pathway for local isolates. We suggest that delayed stimulation of complement-dependent neutrophil migration may account in part for the infrequency of genital symptoms and may contribute to the mechanism of dissemination in patients with systemic gonococcal infection.

Activation of complement by serum-resistant Neisseria gonorrhoeae. Assembly of the membrane attack complex without subsequent cell death

Interaction of the human complement system in normal human serum (NHS) with serum-resistant and -sensitive Neisseria gonorrhoeae was evaluated to better understand the mechanism of serum-resistance. Complement activity (CH50) was depleted from NHS in a dose-dependent fashion by both serum-resistant and -sensitive N. gonorrhoeae. No detectable CH50 remained in NHS incubated with 10(9) colony-forming units (CFU)/ml serum of either resistant or sensitive strains. When smaller numbers of bacteria were incubated with NHS, lesser, yet comparable, amounts of CH50 were depleted by both resistant and sensitive strains. Hemolytic C2 activity was diminished by 33% in the case of resistant N. gonorrhoeae (10(8) CFU/ml serum) and by 48% in the case of a sensitive strain. No detectable decreases in hemolytic C4 or C7 activities were found with either sensitive or resistant strains at this concentration. Both resistant and sensitive strains activated C1s in NHS. Resistant strains specifically activated 19-21% of radiolabeled C1s in NHS, whereas sensitive strains activated 18-32%. Both resistant and sensitive strains also activated C5 in NHS. In binding assays using radiolabeled C5 and C9 in NHS, resistant and sensitive strains bound comparable amounts of C5 and C9. The number of bound C5 and C9 molecules varied according to the number of bacteria or amount of serum used in the assay. The ratio of C9/C5 bound to a sensitive strain was 6.8, and to a resistant strain was 8.2, suggesting that C5 and C9 were incorporated into membrane attack complexes (MAC). Electron microscopic examination of resistant and sensitive strains incubated with NHS revealed that MAC is bound to the surfaces of the resistant strain as well as the sensitive strain.

Neisseria gonorrhoeae isolated from disseminated and localised infections in pre-penicillin era. Auxotypes and antibacterial drug resistances

Interest in the evolution of gonococcal auxotrophy led to a study of 72 strains isolated between 1935 and 1948 from the urogenital tract (57 patients), the eye (two patients), and from disseminated gonococcal infections (11 patients and probably two others). Two cervical isolates with nutritional requirements for proline, arginine, histidine, and biotin were oxidase-positive, Gram-negative diplococci, but their identity as Neisseria gonorrhoeae was uncertain because they were atypically susceptible to colistin and did not produce acid in glucose media. The N gonorrhoeae strains were highly susceptible to 11 other antibacterial drugs but not to sulphadiazine. Defects of one or more pathways for the biosynthesis of methionine, proline, arginine, threonine, lysine, the branched-chain amino acids, hypoxanthine, and thiamine pyrophosphate were found in 39 of the 70 strains, including four isolated in the presulphanilamide era. Unexpectedly, methionine was required for the growth of 11 (21%) of the 52 Danish strains and for 13 (72%) of 18 strains isolated in the USA. The Danish strains included 28 (54%) that did not require any of the compounds used for differentiating auxotypes, whereas this type was represented by only three (17%) of the USA strains. None of the gonococci required uracil or other pyrimidines. This suggests that the requirements for arginine, hypoxanthine, and uracil commonly found in recent isolates from disseminated gonococcal infections probably evolved treatment with sulphonamide was replaced by penicillin.

Auxotypes and antibacterial resistance to gonococci with differing susceptibilities to vancomycin

The responses to vancomycin and 11 other antibacterial drugs and the nutritional requirements of gonococci recovered from two selective media were determined. Single urogenital specimens from 508 patients attending a social hygiene clinic in 1975 yielded 97 strains of Neisseria gonorrhoeae; 95 were recovered on VCNT (a modification of Thayer-Martin medium), always inoculated first, and 69 on LC medium containing lincomycin (4 micrograms/ml) and colistin (5 micrograms/ml). The two drugs at these concentrations in LC medium were not inhibitory for isolates from either medium. Unexpectedly, three isolates on VCNT were susceptible to vancomycin at the concentrations (3 micrograms/ml) in VCNT medium; these three were typically sensitive to penicillins but were hypersusceptible to erythromycin (inhibited by less than or greater than 0.05 micrograms/ml) and rifampin (less than or equal to 0.02 micrograms/ml). Resistance to streptomycin (greater than or equal to 500 micrograms/ml) (22% of the strains) was correlated with increased resistance to penicillins, erythromycin, and rifampin in most instances. All streptomycin-resistant gonococci required proline, or arginine, or none of the test compounds. Strains requiring arginine, hypoxanthine, and uracil were uniformly sensitive to antibiotics but not hypersusceptible. In contrast, six strains of N gonorrhoeae isolated in Denmark required arginine (not satisfied by ornithine), hypoxanthine, and uracil and were hypersusceptible to vancomycin (inhibited by 0.5 micrograms/ml), erythromycin, and rifampin. DNA-mediated transformation showed that all three hypersusceptibilities of one Danish strain were introduced together into a wild-type gonococcus, suggesting that a mutation of an env (envelope) locus might be responsible for the atypical permeability.

Pyocin-resistant lipopolysaccharide mutans of Neisseria gonorrhoeae: alterations in sensitivity to normal human serum and polymyxin B

Pyocins from Pseudomonas aeruginosa were used to select several lipopolysaccharide (LPS) mutants of Neisseria gonorrhoeae strain FA19. Three classes of LPS mutans were found in the initial group selected for study. The LPS of one class lacked galactose. That of a second group lacked the typical heptose found in the parental LPS, was reduced in glucose, galactose, and N-acetylglucosamine content, appeared to contain a new unidentified sugar component, and consisted of two species of LPS separable on sodium dodecyl sulfate-polyacrylamide gels. The LPS of a third strain lacked the heptose, glucose, galactose, and N-acetylglucosamine found in the oligosaccharide portion of parental FA19 LPS. The minimal inhibitory concentration for polymyxin B of the mutant strains was 3 to 4 times that of the parental strain. The strains lacking only galactose were as resistant as the parent to the bactericidal action of normal human serum, but cells of the other two classes were quickly killed by serum. Gonococcal LPS thus appears to be important in determining phenotypic properties of the cells.

Gonococci with mutations to low-level penicillin resistance exhibit increased sensitivity to the oxygen-independent bactericidal activity of human polymorphonuclear leukocyte granule extracts

Gonococci which cause disseminated gonococcal infection are nearly always highly penicillin sensitive, in contrast to many isolates causing uncomplicated gonorrhea. We questioned whether any of the known chromosomal mutations to low-level penicillin resistance might adversely affect virulence. The penA2 locus is known to result in low-level resistance to penicillins, whereas mtr-2 results in nonspecific resistance to a variety of antimicrobial agents. We found that the penA2 and mtr-2 mutations each markedly increased sensitivity of strain FA19 to oxygen-independent killing by human polymorphonuclear leukocyte mixed or isolated azurophilic granule extracts. The penA2 and mtr-2 mutations had no effect on sensitivity to serum antibody and complement. Isogenic opaque or transparent variants of several strains of Neisseria gonorrhoeae were equally resistant to human polymorphonuclear leukocyte mixed granule extract bactericidal systems. There were also no differences in susceptibility of piliated type 1 and nonpiliated type 4 variants to human polymorphonuclear leukocyte mixed granule extracts. Since the penA2 and mtr-2 loci are known to increase the degree of cross-linking of cell wall peptidoglycan, the structure of peptidoglycan apparently affects sensitivity to killing by one or more polymorphonuclear leukocyte azurophilic granule extract bactericidal systems. These observations might explain why gonococci with mutations similar to penA2 and mtr-2 are almost never isolated from patients with disseminated gonococcal infection.

Ability of Neisseria gonorrhoeae, Neisseria meningitidis, and commensal Neisseria species to obtain iron from lactoferrin

The ability of 107 Neisseria isolates to compete for iron with human lactoferrin (LF) was examined. Each of 15 meningococci, 53% of 59 selected gonococci, and 24% of 33 commensal Neisseria could use LF-bound iron for growth. Isolates which could not obtain iron from LF were growth inhibited when sufficient LF was added to defined agar medium to bind available free iron. No difference was observed in the ability of colony type 1 and colony type 4 gonococci of the same strain to compete with LF for iron. LF was growth inhibitory for 50% of 22 disseminated disease isolates (DGI strains) and 51% of 35 local urogenital disease isolates (UGI strains). Only 14% of gonococcal isolates requiring arginine, hypoxanthine, and uracil for growth were able to compete with LF for iron, whereas 87% of all other gonococcal isolates could do so (P less than 0.005). Ability to obtain iron from LF does not appear to be required for survival of Neisseria on mucosal surfaces, nor essential for invasion of the bloodstream by gonococci. However, ability to utilize LF as a source of iron may contribute to differences in pathogenicity among certain gonococcal isolates.

Identification of a new genetic site (sac-3+) in Neisseria gonorrhoeae that affects sensitivity to normal human serum

A previously undescribed genetic site (sac-3) affecting susceptibility of the gonococcus to normal human serum was localized on the gonococcal chromosome. The presence of the sac-3+ allele in a clinical isolate (FA889) resulted in sensitivity only to relatively high concentrations of serum (greater than or equal to 12.5%). Genetic mapping experiments demonstrated that sac-3+ was tightly linked to another genetic site (sac-1+) involved in determining susceptibility to normal human serum and to a locus (nmp-3) involved in the replacement of outer membrane protein I. The sac-1+ and sac-3+ loci resulted in phenotypically distinct levels of sensitivity to human serum. The sac-3+ serum sensitivity and sac-1+ serum sensitivity loci recombined with high frequency, resulting in serum resistance. The results show that serum sensitivity in clinical isolates may be due to different serum sensitivity loci and suggest that different antigens and immunological mechanisms could be responsible for sensitivity of different gonococcal isolates to human serum.

Ability of Neisseria gonorrhoeae, Neisseria meningitidis, and commensal Neisseria species to obtain iron from transferrin and iron compounds

The ability of Neisseria species to use iron compounds and to compete with iron-binding proteins was examined with deferrated defined medium and the iron chelator deferoxamine. All Neisseria species were able to assimilate a variety of ferric and ferrous iron salts. They were not able to efficiently solubilize an inorganic iron salt such as ferric nitrate, but were able to use iron chelated by citrate, oxalacetate, pyrophosphate, or nitrilotriacetate. Each of the 95 Neisseria isolates examined was able to use hemin as a sole source of iron, and most, but not all, of the isolates were able to obtain iron from hemoglobin. Heated human serum stimulated growth of all gonococci, meningococci, and some commensal Neisseria species in iron-deficient medium. All gonococci and meningococci were able to scavenge iron from 25% saturated transferrin, whereas most commensal organisms were inhibited by this iron-binding protein. The ability to compete with transferrin was specific, since partially saturated conalbumin was bacteriostatic for all Neisseria species. Although the pathogenic Neisseria species were able to compete more efficiently with transferrin for iron than were the nonpathogenic Neisseria species, no correlation was observed between the virulence of different strains or colony types of gonococci and the ability to scavenge iron in vitro from transferrin or other chelators.

Genetics of serum resistance in Neisseria gonorrhoeae: the sac-1 genetic locus

A genetic locus affecting susceptibility to the bactericidal activity of normal human serum has been designated sac-1. This locus was shown to be closely linked to, but not identical with, a second locus (designated nmp-2) that affects protein 1 of the outer membrane. The sac-1 locus could be linked to known antibiotic resistance markers on the gonococcal chromosome by genetic transformation.

Auxotypes of Neisseria gonorrhoeae isolated from localized and disseminated infections in Montreal

A survey recently made in the United States on the regional distribution of auxotypes of Neisseria gonorrhoeae suggested that isolates from different geographic areas often differ in auxotype. A subsequent auxotyping study in Montreal of 901 isolates of N. gonorrhoeae, 15 from patients with disseminated gonococcal infection, proved interesting in many regards. Gonococcal genetic medium, modified by the addition of other amino acids, was used. Most (93%) of the strains isolated from patients with localized infection belonged to one of the following three phenotypes: arginine-, hypoxanthine- and uracil-dependent (44%); prototrophic (33%); and proline-dependent (16%). Of the 15 strains responsible for disseminated infection 14 required arginine, hypoxanthine and uracil for growth.

Cotransformation of a serum resistance phenotype with genes for arginine biosynthesis in Neisseria gonorrhoeae

Two genes (arg-3 and arp-6) marked by arginine auxotrophy and a gene (sac-2) marked by resistance to serum killing were found to be linked by cotransformation. Evidence derived from the linkage of these markers to spc (spectinomycin resistance) suggests that sac-2 may be genetically distinct from a sac gene previously described.

Relationship of the interval between infections and the similarity of gonococcal strains in recurrent gonorrhoea

Paired gonococcal isolates from 38 patients with recurrent episodes of gonorrhoea at varying intervals were examined for similarity by means of gonococcal auxotyping and susceptibility to antibiotics. A different gonococcal strain was the cause of the second infection in 53% of the patients. Longer intervals between infections were significantly associated with greater numbers of dissimilar strains as a cause of the second infection. The same strain was usually found in infections occurring within 60 days of each other whereas different strains were more likely to cause infections occurring more than 60 days apart. The isolates causing the second infection were significantly more susceptible to penicillin.

Auxotypes and antimicrobial susceptibilities of Neisseria gonorrhoeae in black and white patients

Isolates of Neisseria gonorrhoeae from 100 white and 113 black patients attending a venereal disease clinic were examined for their susceptibility to ampicillin, penicillin, tetracycline, and spectinomycin. The isolates were also characterised by gonococcal auxotyping. Gonococcal isolates from black patients were more resistant to the antibiotics than those from white patients, since the former were infected with the more antibiotic-resistant auxotypes (Pro, Zero, and Arg) whereas the latter were infected with the more antibiotic-susceptible auxotypes (AHU and others). These data indicate a preferential infection by sub-populations of Neisseria gonorrhoeae in two racial groups.

The microbiology and therapy of acute pelvic inflammatory disease in hospitalized patients

We examined microbial isolates from the endocervical and peritoneal cavity of 30 women hospitalized with acute PID. Patients were randomly assigned to one of two antibiotic regimens: amoxicillin, 6 gm by mouth every 24 hours, or aqueous penicillin G, 30 million units and gentamicin, 180 to 240 mg intravenously every 24 hours. We measured response by quantifying physical examination findings. Neisseria gonorrhoeae was isolated from the cervix of 24 patients (80%) and from the peritoneal cavity of 10 (33%). Other peritoneal isolates included Enterobacteriaceae in five patients, Ureaplasma urealyticum in five, Mycoplasma hominis in six, and Chlamydia trachomatis in three. Bacteroides melaninogenicus, the most frequent anaerobe, was isolated in 11 cases. Bacteroides fragillis was not isolated from any specimen. The cure rates were the same for both regimens: three patients failed on each. Four women required total abdominal hysterectomy and unilateral or bilateral salpingo-oophorectomy.

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.