Ribosomal resistance to streptomycin and spectinomycin in Neisseria gonorrhoeae

High-level in vitro resistance to gentamicin acquired in a stepwise manner in Neisseria gonorrhoeae

OBJECTIVES

Gentamicin is used in several alternative treatments for gonorrhoea. Verified clinical Neisseria gonorrhoeae isolates with gentamicin resistance are mainly lacking and understanding the mechanisms for gonococcal gentamicin resistance is imperative. We selected gentamicin resistance in gonococci in vitro, identified the novel gentamicin-resistance mutations, and examined the biofitness of a high-level gentamicin-resistant mutant.

METHODS

Low- and high-level gentamicin resistance was selected in WHO X (gentamicin MIC = 4 mg/L) on gentamicin-gradient agar plates. Selected mutants were whole-genome sequenced. Potential gentamicin-resistance fusA mutations were transformed into WT strains to verify their impact on gentamicin MICs. The biofitness of high-level gentamicin-resistant mutants was examined using a competitive assay in a hollow-fibre infection model.

RESULTS

WHO X mutants with gentamicin MICs of up to 128 mg/L were selected. Primarily selected fusA mutations were further investigated, and fusAR635L and fusAM520I + R635L were particularly interesting. Different mutations in fusA and ubiM were found in low-level gentamicin-resistant mutants, while fusAM520I was associated with high-level gentamicin resistance. Protein structure predictions showed that fusAM520I is located in domain IV of the elongation factor-G (EF-G). The high-level gentamicin-resistant WHO X mutant was outcompeted by the gentamicin-susceptible WHO X parental strain, suggesting lower biofitness.

CONCLUSIONS

We describe the first high-level gentamicin-resistant gonococcal isolate (MIC = 128 mg/L), which was selected in vitro through experimental evolution. The most substantial increases of the gentamicin MICs were caused by mutations in fusA (G1560A and G1904T encoding EF-G M520I and R635L, respectively) and ubiM (D186N). The high-level gentamicin-resistant N. gonorrhoeae mutant showed impaired biofitness.

Antimicrobial resistance prediction in Neisseria gonorrhoeae: Current status and future prospects

INTRODUCTION

Several nucleic acid amplification tests (NAATs), mostly real-time PCRs, to detect antimicrobial resistance (AMR) determinants and predict AMR in Neisseria gonorrhoeae are promising, and some may be ready to apply at the point-of-care (POC), but important limitations remain with most NAATs. Next-generation sequencing (NGS) can overcome many of these limitations.Areas covered: Recent advances, with main focus on publications since 2017, in the development and use of NAATs and NGS to predict gonococcal AMR for surveillance and clinical use, and pros and cons of these tests as well as future perspectives for appropriate use of molecular AMR prediction for N. gonorrhoeae.Expert Commentary: NAATs and/or NGS for AMR prediction should supplement culture-based AMR surveillance, which will remain because it detects also AMR due to unknown AMR determinants, and translation into POC tests is imperative for the end-goal of individualized treatment, sparing ceftriaxone±azithromycin. Several challenges for direct testing of clinical, especially pharyngeal, specimens and for accurate prediction of cephalosporins and azithromycin resistance, especially using NAATs, remain. The choice of AMR prediction assay needs to carefully consider the intended use of the assay; limitations intrinsic to the AMR prediction technology, algorithms and specific to chosen methodology; specimen types analyzed; and cost-effectiveness.

Molecular Insight into TdfH-Mediated Zinc Piracy from Human Calprotectin by Neisseria gonorrhoeae

The dramatic rise in antimicrobial resistance among Neisseria gonorrhoeae isolates over the last few decades, paired with dwindling treatment options and the lack of a protective vaccine, has prompted increased interest in identifying new bacterial targets for the treatment and, ideally, prevention of gonococcal disease. TonB-dependent transporters are a conserved set of proteins that serve crucial functions for bacterial survival within the host. In this study, binding between the gonococcal transporter, TdfH, and calprotectin was determined to be of high affinity and host restricted. The current study identified a preferential TdfH interaction at the calprotectin dimer interface. An antigonococcal therapeutic could potentially block this site on calprotectin, interrupting Zn uptake by N. gonorrhoeae and thereby prohibiting continued bacterial growth. We describe protein-protein interactions between TdfH and calprotectin, and our findings provide the building blocks for future therapeutic or prophylactic targets.

Neisseria gonorrhoeae, responsible for the sexually transmitted infection gonorrhea, is an obligate human pathogen exquisitely adapted for survival on mucosal surfaces of humans. This host-pathogen relationship has resulted in evolution by N. gonorrhoeae of pathways that enable the use of host metalloproteins as required nutrients through the deployment of outer membrane-bound TonB-dependent transporters (TdTs). Recently, a TdT called TdfH was implicated in binding to calprotectin (CP) and in removal of the bound zinc (Zn), enabling gonococcal growth. TdfH is highly conserved among the pathogenic Neisseria species, making it a potentially promising candidate for inclusion into a gonococcal vaccine. Currently, the nature and specificity of the TdfH-CP interaction have not been determined. In this study, we found that TdfH specifically interacted with human calprotectin (hCP) and that growth of the gonococcus was supported in a TdfH-dependent manner only when hCP was available as a sole zinc source and not when mouse CP was provided. The binding interactions between TdfH and hCP were assessed using isothermal titration calorimetry where we observed a multistate model having both high-affinity and low-affinity sites of interaction. hCP has two Zn binding sites, and gonococcal growth assays using hCP mutants deficient in one or both of the Zn binding sites revealed that TdfH exhibited a site preference during Zn piracy and utilization. This report provides the first insights into the molecular mechanism of Zn piracy by neisserial TdfH and further highlights the obligate human nature of N. gonorrhoeae and the high-affinity interactions occurring between TdTs and their human ligands during pathogenesis.

The drug tolerant persisters of Riemerella anatipestifer can be eradicated by a combination of two or three antibiotics

Background

Riemerella anatipestifer (RA), the causative agent of duck infectious serositis, leads to high mortality in duck flocks and great economic losses in duck industry. Previous studies on RA are largely focused on its detection, virulence factors, serology, epidemiology as well as antibiotic resistance. Neither drug tolerant persisters nor the persister level under the treatment of antibiotics has been revealed. The persisters are non-growing or dormant cells within an isogenic bacterial population; they play important roles in recurrent infection and formation of drug resistant mutants. The aim of this study is to detect the drug tolerant persisters from the exponentially grown population of RA reference strain (RA 11845) or RA clinical isolate (RA TQ3), and address whether a single antibiotic or a combination of two or three antimicrobials can eradicate the persisters at respective maximum serum/plasma concentration (C_max).

Result

With the concentration of a test antibiotic increased, a small fraction of cells in the exponentially grown culture of RA reference strain (RA 11845) or RA clinical isolate (RA TQ3) always survived, irrespective of treatment time, indicating the presence of drug tolerant presisters. A single antibiotic cannot eradicate the persisters of both RA strains at respective C_max, except that the C_max of ceftiofur wiped out the population of the reference strain (RA 11845). Besides, the clinical isolate RA TQ3 presented a higher tolerance to ceftiofur in comparison to that of the reference strain (RA 11845). Combination of any two or three antimicrobials eliminated the drug tolerant persisters of RA TQ3 completely at respective C_max.

Conclusion

A sub-community of drug tolerant persisters was present in RA population. Persisters of RA TQ3 are single drug tolerant and not multidrug tolerant persisters.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1303-8) contains supplementary material, which is available to authorized users.

Neisseria gonorrhoeae Evades Calprotectin-Mediated Nutritional Immunity and Survives Neutrophil Extracellular Traps by Production of TdfH

Neisseria gonorrhoeae successfully overcomes host strategies to limit essential nutrients, termed nutritional immunity, by production of TonB-dependent transporters (TdTs)-outer membrane proteins that facilitate nutrient transport in an energy-dependent manner. Four gonococcal TdTs facilitate utilization of iron or iron chelates from host-derived proteins, including transferrin (TbpA), lactoferrin (LbpA), and hemoglobin (HpuB), in addition to xenosiderophores from other bacteria (FetA). The roles of the remaining four uncharacterized TdTs (TdfF, TdfG, TdfH, and TdfJ) remain elusive. Regulatory data demonstrating that production of gonococcal TdfH and TdfJ are unresponsive to or upregulated under iron-replete conditions led us to evaluate the role of these TdTs in the acquisition of nutrients other than iron. In this study, we found that production of gonococcal TdfH is both Zn and Zur repressed. We also found that TdfH confers resistance to calprotectin, an immune effector protein highly produced in neutrophils that has antimicrobial activity due to its ability to sequester Zn and Mn. We found that TdfH directly binds calprotectin, which enables gonococcal Zn accumulation in a TdfH-dependent manner and enhances bacterial survival after exposure to neutrophil extracellular traps (NETs). These studies highlight Zn sequestration by calprotectin as a key functional arm of NET-mediated killing of gonococci. We demonstrate for the first time that N. gonorrhoeae exploits this host strategy in a novel defense mechanism, in which TdfH production hijacks and directly utilizes the host protein calprotectin as a zinc source and thereby evades nutritional immunity.

Proteomics of Neisseria gonorrhoeae: the treasure hunt for countermeasures against an old disease

Neisseria gonorrhoeae is an exquisitely adapted, strictly human pathogen and the causative agent of the sexually transmitted infection gonorrhea. This ancient human disease remains a serious problem, occurring at high incidence globally and having a major impact on reproductive and neonatal health. N. gonorrhoeae is rapidly evolving into a superbug and no effective vaccine exists to prevent gonococcal infections. Untreated or inadequately treated gonorrhea can lead to severe sequelae, including pelvic inflammatory disease and infertility in women, epididymitis in men, and sight-threatening conjunctivitis in infants born to infected mothers. Therefore, there is an immediate need for accelerated research toward the identification of molecular targets for development of drugs with new mechanisms of action and preventive vaccine(s). Global proteomic approaches are ideally suited to guide these studies. Recent quantitative proteomics (SILAC, iTRAQ, and ICAT) have illuminated the pathways utilized by N. gonorrhoeae to adapt to different lifestyles and micro-ecological niches within the host, while comparative 2D SDS-PAGE analysis has been used to elucidate spectinomycin resistance mechanisms. Further, high-throughput examinations of cell envelopes and naturally released membrane vesicles have unveiled the ubiquitous and differentially expressed proteins between temporally and geographically diverse N. gonorrhoeae isolates. This review will focus on these different approaches, emphasizing the role of proteomics in the search for vaccine candidates. Although our knowledge of N. gonorrhoeae has been expanded, still far less is known about this bacterium than the closely related N. meningitidis, where genomics- and proteomics-driven studies have led to the successful development of vaccines.

Reference map and comparative proteomic analysis of Neisseria gonorrhoeae displaying high resistance against spectinomycin

A proteome reference map of Neisseria gonorrhoeae was successfully established using two-dimensional gel electrophoresis in conjunction with matrix-assisted laser desorption ionization-time of flight mass spectrometry. This map was further applied to compare protein expression profiles of high-level spectinomycin-resistant (clinical isolate) and -susceptible (reference strain) N. gonorrhoeae following treatment with subminimal inhibitory concentrations (subMICs) of spectinomycin. Approximately 200 protein spots were visualized by Coomassie brilliant blue G-250 staining and 66 spots representing 58 unique proteins were subsequently identified. Most of the identified proteins were analysed as cytoplasmic proteins and belonged to the class of energy metabolism. Comparative proteomic analysis of whole protein expression of susceptible and resistant gonococci showed up to 96% similarity while eight proteins were found to be differentially expressed in the resistant strain. In the presence of subMICs of spectinomycin, it was found that 50S ribosomal protein L7/L12, an essential component for ribosomal translocation, was upregulated in both strains, ranging from 1.5- to 3.5-fold, suggesting compensatory mechanisms of N. gonorrhoeae in response to antibiotic that inhibits protein synthesis. Moreover, the differential expression of proteins involved in energy metabolism, amino acid biosynthesis, and the cell envelope was noticeably detected, indicating significant cellular responses and adaptation against antibiotic stress. Such knowledge provides valuable data, not only fundamental proteomic data, but also knowledge of the mode of action of antibiotic and secondary target proteins implicated in adaptation and compensatory mechanisms.

Mutation in ribosomal protein S5 leads to spectinomycin resistance in Neisseria gonorrhoeae

Spectinomycin remains a useful reserve option for therapy of gonorrhea. The emergence of multidrug-resistant Neisseria gonorrhoeae strains with decreased susceptibility to cefixime and to ceftriaxone makes it the only medicine still effective for treatment of gonorrhea infection in analogous cases. However, adoption of spectinomycin as a routinely used drug of choice was soon followed by reports of spectinomycin resistance. The main molecular mechanism of spectinomycin resistance in N. gonorrhoeae was C1192T substitution in 16S rRNA genes. Here we reported a Thr-24→Pro mutation in ribosomal protein S5 (RPS5) found in spectinomycin resistant clinical N. gonorrhoeae strain, which carried no changes in 16S rRNA. In a series of experiments, the transfer of rpsE gene allele encoding the mutant RPS5 to the recipient N. gonorrhoeae strains was analyzed. The relatively high rate of transformation [ca. 10⁻⁵ colony-forming units (CFUs)] indicates the possibility of spread of spectinonycin resistance within gonococcal population due to the horizontal gene transfer (HGT).

Novel aminoglycoside 2''-phosphotransferase identified in a gram-negative pathogen

Aminoglycoside 2″-phosphotransferases are the major aminoglycoside-modifying enzymes in clinical isolates of enterococci and staphylococci. We describe a novel aminoglycoside 2″-phosphotransferase from the Gram-negative pathogen Campylobacter jejuni, which shares 78% amino acid sequence identity with the APH(2″)-Ia domain of the bifunctional aminoglycoside-modifying enzyme aminoglycoside (6') acetyltransferase-Ie/aminoglycoside 2″-phosphotransferase-Ia or AAC(6')-Ie/APH(2″)-Ia from Gram-positive cocci, which we called APH(2″)-If. This enzyme confers resistance to the 4,6-disubstituted aminoglycosides kanamycin, tobramycin, dibekacin, gentamicin, and sisomicin, but not to arbekacin, amikacin, isepamicin, or netilmicin, but not to any of the 4,5-disubstituted antibiotics tested. Steady-state kinetic studies demonstrated that GTP, and not ATP, is the preferred cosubstrate for APH(2″)-If. The enzyme phosphorylates the majority of 4,6-disubstituted aminoglycosides with high catalytic efficiencies (k(cat)/K(m) = 10(5) to 10(7) M(-1) s(-1)), while the catalytic efficiencies against the 4,6-disubstituted antibiotics amikacin and isepamicin are 1 to 2 orders of magnitude lower, due mainly to the low apparent affinities of these substrates for the enzyme. Both 4,5-disubstituted antibiotics and the atypical aminoglycoside neamine are not substrates of APH(2″)-If, but are inhibitors. The antibiotic susceptibility and substrate profiles of APH(2″)-If are very similar to those of the APH(2″)-Ia phosphotransferase domain of the bifunctional AAC(6')-Ie/APH(2″)-Ia enzyme.

Cephalosporin Resistance in Neisseria gonorrhoeae

Gonorrhea, a disease of public health importance, not only leads to high incidence of acute infections and complications but also plays a major role in facilitating human immunodeficiency virus (HIV) acquisition and transmission. One of the major public health needs for gonorrhea control is appropriate, effective treatment. However, treatment options for gonorrhea are diminishing as Neisseria gonorrhoeae have developed resistance to several antimicrobial drugs such as sulfonamides, penicillin, tetracyclines and quinolones. Antimicrobial resistance (AMR) surveillance of N. gonorrhoeae helps establish and maintain the efficacy of standard treatment regimens. AMR surveillance should be continuous to reveal the emergence of new resistant strains, monitor the changing patterns of resistance, and be able to update treatment recommendations so as to assist in disease control. Current treatment guidelines recommend the use of single dose injectable or oral cephalosporins. The emergence and spread of cephalosporin resistant and multi drug resistant N. gonorrhoeae strains, represents a worrying trend that requires monitoring and investigation. Routine clinical laboratories need to be vigilant for the detection of such strains such that strategies for control and prevention could be reviewed and revised from time to time. It will be important to elucidate the genetic mechanisms responsible for decreased susceptibility and future resistance. There is also an urgent need for research of safe, alternative anti-gonococcal compounds that can be administered orally and have effective potency, allowing high therapeutic efficacy (greater than 95.0% cure rate).

Update on the management of gonorrhea in adults in the United States

Gonorrhea, the second most commonly reported notifiable disease, is an important cause of cervicitis, urethritis, and pelvic inflammatory disease. The selection of appropriate therapy for gonorrhea (i.e., safe, highly effective, single dose, and affordable) is complicated by the ability of Neisseria gonorrhoeae to develop resistance to antimicrobial therapies. This article reviews the key questions and data that informed the 2006 gonorrhea treatment recommendations of the Centers for Disease Control and Prevention. Key areas addressed include the criteria used to select effective treatment for gonorrhea, the level of antimicrobial resistance at which changing treatment regimens is recommended, the epidemiology of resistance, and the use of quinolones, cephalosporins, and other classes of antimicrobials for the treatment of uncomplicated gonorrhea.

Versatility of aminoglycosides and prospects for their future

Aminoglycoside antibiotics have had a major impact on our ability to treat bacterial infections for the past half century. Whereas the interest in these versatile antibiotics continues to be high, their clinical utility has been compromised by widespread instances of resistance. The multitude of mechanisms of resistance is disconcerting but also illuminates how nature can manifest resistance when bacteria are confronted by antibiotics. This article reviews the most recent knowledge about the mechanisms of aminoglycoside action and the mechanisms of resistance to these antibiotics.

Current concepts in the management of gonorrhoea

The incidence of gonorrhoea is again rising in developed countries and a high disease rate has been maintained in less developed regions for a number of years. The need not only for treatment of the individual but also for control of gonorrhoea at a community level has increased significantly following recognition of its role in the amplification of human immunodeficiency virus (HIV) transmission. A sustainable decrease in the incidence of gonorrhoea and other sexually transmitted diseases (STDs) requires an integrated approach combining improved prevention, better diagnosis and optimal treatment. Effective antibiotic treatment is an essential element of this approach. However, antibiotic treatment of gonorrhoea has been severely hampered by the development of antibiotic resistance in Neisseria gonorrhoeae, to the extent that many therapies are no longer effective. Those treatments that retain acceptable efficacy are often unaffordable where they are most needed. Penicillins and tetracyclines should no longer be used in gonococcal disease, there are limitations on the effectiveness of newer macrolides and spectinomycin and in many parts of the world quinolones have been withdrawn from schedules for the treatment of gonorrhoea. Of all the current agents used to treat all forms of gonococcal disease, only the third generation cephalosporins (most notably ceftriaxone) have retained their efficacy; however, decreased susceptibility to these antibiotics has also appeared. Continuing reliance on antibiotic treatment for controlling gonorrhoea in the absence of other necessary approaches will see a further deterioration in the situation. In these circumstances the possibility that gonorrhoea will be untreatable becomes more real.

Antimicrobial agents and gonorrhoea: therapeutic choice, resistance and susceptibility testing

INTRODUCTION

Neisseria gonorrhoeae, the causative agent of gonorrhoea is a particularly well adapted pathogen that has continued to evolve mechanisms to evade treatment with antimicrobial agents.

THERAPEUTIC CHOICE

The choice of antibiotic for use in the first-line treatment of gonorrhoea should be made with knowledge of the susceptibility of the isolates of N gonorrhoeae to be encountered.

RESISTANCE

High-level resistance to penicillin and tetracycline in N gonorrhoeae is plasmid-mediated and a major therapeutic problem. Penicillinase-producing N gonorrhoeae, first described in 1976, have now spread worldwide and tetracycline-resistant N gonorrhoeae, described in 1985, are becoming increasingly prevalent. Chromosomal resistance to penicillin is low-level and affects a range of antibiotics. High-level resistance to spectinomycin has been sporadic and has not limited its use whereas the emergence of resistance to ciprofloxacin will have a significant impact on its use for gonorrhoea.

SUSCEPTIBILITY TESTING

A variety of methods are available including disc diffusion, breakpoint agar dilution technique, E-test and determination of the minimum inhibitory concentration (MIC). The choice of methodology will depend on the number and type of isolates and the facilities available for testing.

DISCUSSION

Surveillance programmes to monitor levels of antibiotic resistant isolates are essential to ensure therapeutic success.

In vitro antibacterial activity of trospectomycin (U-63366F), a novel spectinomycin analog

Trospectomycin (U-63366F) is a novel spectinomycin analog with broad-spectrum antibacterial activity. The in vitro activity of this analog was compared with that of spectinomycin and other reference antibiotics against 411 clinical isolates of aerobic and anaerobic bacteria. MICs were determined by agar or broth dilution methods. The stability of trospectomycin in the presence of an enzyme extract derived from spectinomycin-resistant Escherichia coli was determined. Trospectomycin was more active than spectinomycin (4- to 32-fold) against strains of numerous bacterial species, including staphylococci, streptococci, Haemophilus influenzae, Branhamella catarrhalis, Neisseria gonorrhoeae, Proteus species, Bacteroides species, Clostridium difficile, Clostridium species, and Chlamydia trachomatis. Trospectomycin demonstrated a moderate level of activity (comparable to that of spectinomycin) for most species of the family Enterobacteriaceae tested and was generally cross resistant with spectinomycin. Trospectomycin was susceptible to inactivation by crude enzyme preparations from spectinomycin-inactivating strains of E. coli. Trospectomycin inhibited a variety of clinically important organisms, including agents of sexually transmitted diseases and pelvic inflammatory disease. Clinical studies with this novel aminocyclitol antibiotic are in progress.

Effect of spectinomycin use on the prevalence of spectinomycin-resistant and of penicillinase-producing Neisseria gonorrhoeae

Because of the high prevalence of penicillinase-producing Neisseria gonorrhoeae in the Republic of Korea, spectinomycin has been used there in the primary treatment of gonococcal infections in U.S. military personnel since 1981, but there have been increasingly frequent reports of treatment failures with spectinomycin. We conducted a clinical study to determine the efficacy of spectinomycin treatment in 124 U.S. servicemen in the Republic of Korea who had urethral gonococcal infections. Ninety-seven patients were treated with spectinomycin alone and evaluated in a follow-up visit. In eight patients (8.2 percent), this treatment was unsuccessful. Antibiotic-sensitivity testing on isolates from seven of the patients with treatment failure demonstrated that six isolates were highly resistant to spectinomycin (minimal inhibitory concentration, greater than or equal to 100 micrograms per milliliter). None of the spectinomycin-resistant strains had become resistant to penicillin, either through the production of penicillinase or through a chromosomal mutation. Although the mechanism of spectinomycin resistance appears to be a chromosomal mutation, these isolates were generally sensitive to other antibiotics. The prevalence of resistance to spectinomycin resulted in the substitution of ceftriaxone for the primary treatment of gonorrhea acquired by U.S. military personnel in the Republic of Korea. We believe that the rapid emergence of spectinomycin resistance in this population mandates a cautious approach to widescale use of the drug and indicates a need to broaden current surveillance programs.

Identification of Eikenella corrodens and Cardiobacterium hominis by genetic transformation

Genetic transformation was employed to attain exact identification of Eikenella corrodens and Cardiobacterium hominis. The two species appeared both homogeneous and without genetic affinity to each other or to species of Kingella, Neisseria, and Moraxella, as tested for by rather sensitive procedures with streptomycin- and spectinomycin-resistance markers.

Ribosomal resistance of clinical enterococcal to streptomycin isolates

The mechanism of high-level resistance to streptomycin was studied in 12 clinical isolates of Streptococcus faecalis. Six strains produced streptomycin-modifying enzymes. Each of three enzyme-negative strains tested demonstrated ribosomal resistance to streptomycin. Lack of ribosomal susceptibility is a significant cause of high-level streptomycin resistance among clinical enterococcal isolates.

Spectinomycin resistant gonococci

A study was conducted examining the properties of 10 clinical isolates of spectinomycin resistant gonococci from patients attending clinics at St Mary's and St Thomas's Hospitals, London. All of the isolates produced beta-lactamase and contained plasmids of 2.6, 4.4, and 24.5 megadaltons and required proline for growth. None produced aminoglycoside modifying enzymes. Resistance to spectinomycin was transferred from some of the isolates by transformation but at a much lower frequency than resistance to streptomycin. The isolates from St Mary's Hospital were detected after therapy with spectinomycin, whereas those from St Thomas's Hospital were not. Four recent non-beta-lactamase producing gonococci isolated at St Mary's Hospital and two isolated at St Thomas's Hospital also were not related to use of spectinomycin.

Treatment of uncomplicated gonorrhoea in women. Comparison of rosoxacin and spectinomycin

A comparative study of the new antibacterial agent, rosoxacin, a quinoline derivative, with spectinomycin was made in women with uncomplicated cervical, urethral, pharyngeal, and rectal gonorrhoea. Rosoxacin was given in three oral regimens: 200 mg in a single dose, 300 mg in a single dose, and 300 mg in two doses of 150 mg four hours apart. All culture results 72 hours after administration were negative for Neisseria gonorrhoeae in all 81 women compared with 107 of 109 who received 2 g spectinomycin intramuscularly. Thirty-five of the women successfully treated with rosoxacin harboured penicillinase-producing strains of N gonorrhoeae (PPNG) and 46 non-penicillinase-producing (non-PPNG) strains. Fifty of the women treated with spectinomycin had PPNG strains and 59 non-PPNG strains. Mild self-limiting side effects, principally dizziness, occurred in varying frequency with rosoxacin, but these were difficult to evaluate owing to the characteristics of the patient population and the conditions under which the study was conducted.

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.

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.

Plasmid-mediated chromosomal gene transfer in Neisseria gonorrhoeae

An indigenous Neisseria gonorrhoeae conjugative plasmid, pLE2450, was tested for its ability to mediate chromosomal gene transfer between gonococcal strains. Plasmid-mediated chromosomal transfer was detected at a low frequency and can be used to establish certain linkage relationships between amino acid and antibiotic resistance markers.

Spectinomycin versus tetracycline for the treatment of gonorrhea

Spectinomycin and tetracycline are alternative drugs to penicillin in the treatment of gonorrhea. To compare the efficacy of these agents and their propensity to select resistant gonococci, we treated 4043 patients randomly with either 2 or 4 g of spectinomycin once or 9 g of oral tetracycline for four days. Minimum cure rate for anogenital gonorrhea was 94 per cent with either drug. Oropharyngeal infection responded poorly to spectinomycin in men, with failure of therapy in six of 11. Postgonococcal urethritis in men was less common after tetracycline than after spectinomycin (P less than 0.005). Spectinomycin failure was not related to drug resistance. Tetracycline failure correlated with resistance (P less than 0.0002); one fifth of the isolates resistant to 1.0 mug per milliter of tetracycline were not eradicated. For several reasons, including the appearance of beta-lactamase-producing gonococci, it is no longer clear that penicillin G is the "drug of choice" for gonorrhea. Spectinomycin and tetracycline are equally acceptable alternatives, each with distinct advantages and disadvantages.

Absence of penicillin-degrading enzymes in penicillin-resistant strains of Neisseria gonorrhoeae

Penicillin-resistant and -susceptible strains of Neisseria gonorrhoeae were evaluated for the presence of enzymes capable of degrading penicillin by incubation of [(14)C]benzylpenicillin with resting-cell suspensions of N. gonorrhoeae followed by extraction and chromatography of the labeled antibiotic. No degradative activity was observed.

Inheritance of low-level resistance to penicillin, tetracycline, and chloramphenicol in Neisseria gonorrhoeae

The genetics of low-level resistance to penicillin and other antibiotics in a clinical isolate and a multistep laboratory mutant of Neisseria gonorrhoea was studied by transformation. Mutations at three loci affected sensitivity to penicillin. Mutation at penA resulted in an eightfold increase in resistance to penicillin without affecting response to other antimicrobial agents. Mutation at ery resulted in a two- to fourfold increase in resistance to penicillin and similar increases in resistance to many other antibiotics, dyes, and detergents. Mutation at penB resulted in a fourfold increase in resistance to penicillin and tetracycline, the phenotypic expression of which was dependent on the presence of mutation at ery. The cumulative effect of mutations at penA, ery, and penB was an approximate 128-fold increase in penicillin resistance, to a minimum inhibitory concentration of 1.0 mug/ml. Low-level resistance to tetracycline or chloramphenicol was due to similar additive effects between mutations at the nonspecific ery and penB loci and a locus specific for resistance to each drug (tet and chl, respectively). No evidence was found for penicillinases or other drug-inactivating enzymes.

Loss of low-level antibiotic resistance in Neisseria gonorrhoeae due to env mutations

Mutations (env) which resulted in increased sensitivity of gonococci to diverse compounds were studied by transformation. Strains carrying an env mutation were more sensitive than wild-type strains to several antibiotics, dyes, and detergents. The env mutations resulted in complete phenotypic suppression of low-level resistance to these same drugs determined by mutation at ery. Recombination was observed in transformation crosses between various env mutants. The env locus was not linked to the cluster of antibiotic resistance genes near str and spc.

Genetic mapping of linked antibiotic resistance loci in Neisseria gonorrhoeae

Loci for resistance to several antibiotics in laboratory-derived strains of Neisseria gonorrhoeae were mapped by genetic transformation. Genes for high-level resistance to streptomycin (str) and spectinomycin (spc) and for low-level resistance to tetracycline (tet) and chloramphenicol (chl) were linked. Also, a locus for high-level resistance to rifampin (rif) was linked to str and tet. The apparent order was rif... str... tet... chl... spc. Loci for resistance to other antibiotics (penicillin, erythromycin) were transferred independently of each other and were not linked to the cluster around str. Similar linkage relationships were found with str, tet, chl, and spc loci obtained from naturally occurring (clinical) isolates of N. gonorrhoeae.