Fluoroquinolone treatment failure in gonorrhea. Emergence of a Neisseria gonorrhoeae strain with enhanced resistance to fluoroquinolones

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.

Transferable Mechanisms of Quinolone Resistance from 1998 Onward

While the description of resistance to quinolones is almost as old as these antimicrobial agents themselves, transferable mechanisms of quinolone resistance (TMQR) remained absent from the scenario for more than 36 years, appearing first as sporadic events and afterward as epidemics. In 1998, the first TMQR was soundly described, that is, QnrA. The presence of QnrA was almost anecdotal for years, but in the middle of the first decade of the 21st century, there was an explosion of TMQR descriptions, which definitively changed the epidemiology of quinolone resistance. Currently, 3 different clinically relevant mechanisms of quinolone resistance are encoded within mobile elements: (i) target protection, which is mediated by 7 different families of Qnr (QnrA, QnrB, QnrC, QnrD, QnrE, QnrS, and QnrVC), which overall account for more than 100 recognized alleles; (ii) antibiotic efflux, which is mediated by 2 main transferable efflux pumps (QepA and OqxAB), which together account for more than 30 alleles, and a series of other efflux pumps (e.g., QacBIII), which at present have been sporadically described; and (iii) antibiotic modification, which is mediated by the enzymes AAC(6')Ib-cr, from which different alleles have been claimed, as well as CrpP, a newly described phosphorylase.

Antimicrobial Susceptibility of Neisseria gonorrhoeae in Japan from 2000 to 2015

BACKGROUND

Gonococcal infections are difficult to treat because of their multidrug antimicrobial resistance. The outbreak of antimicrobial-resistant Neisseria gonorrhoeae has begun in Asia and particularly in Japan. Therefore, it is very important that we understand the trend of antimicrobial resistance of N. gonorrhoeae in Asia including Japan. Our surveillance of the antimicrobial susceptibility of N. gonorrhoeae began in 2000 under the guidance of the Department of Urology, Gifu University. We report our surveillance data from 2000 to 2015.

METHODS

We collected N. gonorrhoeae strains isolated from patients with gonococcal infections who visited our cooperating medical institutions in Japan from 2000 to 2015. MICs of penicillin G, cefixime, ceftriaxone, tetracycline, spectinomycin, azithromycin, and levofloxacin were determined by the agar dilution method approved by the Clinical and Laboratory Standards Institute.

RESULTS

From 2000 to 2015, 2471 isolates of N. gonorrhoeae were collected in Japan. High rates of nonsusceptibility to penicillin, tetracycline, levofloxacin, cefixime, and azithromycin were shown. Around 5% to 10% of the strains isolated had a 0.25-mg/L MIC of ceftriaxone in each year, and 6 strains (0.24%) with a 0.5-mg/L MIC of ceftriaxone were isolated throughout the study period. Approximately 5% to 10% of the strains were resistant to each of ceftriaxone, azithromycin, and levofloxacin according to European Committee on Antimicrobial Susceptibility Testing breakpoints, and the rate has not increased significantly.

CONCLUSIONS

From this study and previous pharmacodynamic analyses, a single 1-g dose of ceftriaxone is recommended to treat gonorrhea. As strains with high-level ceftriaxone resistance continue to spread, higher doses of ceftriaxone in monotherapy or multiple doses of ceftriaxone should be considered.

Antimicrobial resistance in Neisseria gonorrhoeae: history, molecular mechanisms and epidemiological aspects of an emerging global threat

Neisseria gonorrhoeae is the agent of gonorrhea, a sexually transmitted infection with an estimate from The World Health Organization of 78 million new cases in people aged 15-49 worldwide during 2012. If left untreated, complications may include pelvic inflammatory disease and infertility. Antimicrobial treatment is usually effective; however, resistance has emerged successively through various molecular mechanisms for all the regularly used therapeutic agents throughout decades. Detection of antimicrobial susceptibility is currently the most critical aspect for N. gonorrhoeae surveillance, however poorly structured health systems pose difficulties. In this review, we compiled data from worldwide reports regarding epidemiology and antimicrobial resistance in N. gonorrhoeae, and highlight the relevance of the implementation of surveillance networks to establish policies for gonorrhea treatment.

Multidrug-resistant gonorrhea: A research and development roadmap to discover new medicines

Emilie Alirol and colleagues discuss the development of new treatments for gonorrhea.

Impact of fluoroquinolone resistance mutations on gonococcal fitness and in vivo selection for compensatory mutations

BACKGROUND

Quinolone-resistant Neisseria gonorrhoeae (QRNG) arise from mutations in gyrA (intermediate resistance) or gyrA and parC (resistance). Here we tested the consequence of commonly isolated gyrA(91/95) and parC86 mutations on gonococcal fitness.

METHODS

Mutant gyrA(91/95) and parC86 alleles were introduced into wild-type gonococci or an isogenic mutant that is resistant to macrolides due to an mtrR(-79) mutation. Wild-type and mutant bacteria were compared for growth in vitro and in competitive murine infection.

RESULTS

In vitro growth was reduced with increasing numbers of mutations. Interestingly, the gyrA(91/95) mutation conferred an in vivo fitness benefit to wild-type and mtrR(-79) mutant gonococci. The gyrA(91/95), parC86 mutant, in contrast, showed a slight fitness defect in vivo, and the gyrA(91/95), parC86, mtrR(-79) mutant was markedly less fit relative to the parent strains. A ciprofloxacin-resistant (Cip(R)) mutant was selected during infection with the gyrA(91/95), parC86, mtrR(-79) mutant in which the mtrR(-79) mutation was repaired and the gyrA(91) mutation was altered. This in vivo-selected mutant grew as well as the wild-type strain in vitro.

CONCLUSIONS

gyrA(91/95) mutations may contribute to the spread of QRNG. Further acquisition of a parC86 mutation abrogates this fitness advantage; however, compensatory mutations can occur that restore in vivo fitness and maintain Cip(R).

Importance of drug resistance in gonococci: from mechanisms to monitoring

Neisseria gonorrhoeae isolates continue to develop an impressive arsenal of resistance mechanisms to antimicrobial agents, including resistance to some of the antibiotics presently recommended for the treatment of gonococcal infections.

Molecular characterization of Neisseria gonorrhoeae identifies transmission and resistance of one ciprofloxacin-resistant strain

A highly discriminative and objective genetic characterization of N. gonorrhoeae, which increases our knowledge of strain populations in different geographic areas, is crucial for the development of improved control measures. In the present study, conventional phenotypic characterization and genetic characterization by means of pulsed-field gel electrophoresis (PFGE), sequencing of the entire porB gene, N. gonorrhoeae multiantigen sequence typing (NG-MAST), and pyrosequencing of a quinolone resistance determining region (QRDR) of the gyrA gene of Swedish ciprofloxacin-resistant N. gonorrhoeae serovar IB-10 isolates (n=45) were performed. The genetic characterization identified one widely spread ciprofloxacin-resistant N. gonorrhoeae ST147 strain. In addition, isolates with slightly different genetic characteristics, which presumably reflect the ongoing evolution only, were also identified. All the isolates contained single nucleotide polymorphisms in QRDR of the gyrA gene that are highly correlated with ciprofloxacin resistance. Consequently, comprehensive characterization identified the first confirmed large domestic transmission, mainly among young heterosexuals, of one ciprofloxacin-resistant N. gonorrhoeae strain in Swedish society during 2002-2003. In conclusion, a precise, i.e. genetic, characterization for identification of individual strains is a very valuable support to the crucial active surveillance of the epidemiological characteristics and the antibiotic susceptibility of N. gonorrhoeae in the effective treatment of gonorrhoea.

Detection of gyrA mutations associated with ciprofloxacin resistance in Neisseria gonorrhoeae by rapid and reliable pre-programmed short DNA sequencing

Quinolone resistance is rapidly increasing in Neisseria gonorrhoeae and is posing a significant public health threat that requires constant surveillance. A rapid and reliable mutation detection assay has been developed. The assay is based on pre-programmed short DNA sequencing and is designed to detect point mutations in the gyrA gene that are highly related to ciprofloxacin resistance, i.e. in codons 91 and 95. By developing an assay based on pyrosequencing and exploiting the pre-programmed nucleotide dispensation capability of this technology, the sequence comprising the mutations will be analysed and promptly reveal whether the N. gonorrhoeae pathogen carries resistance to ciprofloxacin. A panel of 40 N. gonorrhoeae clinical isolates, of which 27 phenotypically displayed decreased susceptibility or resistance to ciprofloxacin, was used in the present study. All point mutations in the short stretch of the N. gonorrhoeae gyrA gene were easily discriminated, and the genotypic results obtained by pre-programmed sequencing were mainly in agreement with the phenotypically identified decreased susceptibility or resistance to ciprofloxacin. The new method used in the present study has the potential for rapid and reliable identification of known as well as previously unknown drug resistance mutations.

Cultivation of Neisseria gonorrhoeae in liquid media and determination of its in vitro susceptibilities to quinolones

The cultivation of Neisseria gonorrhoeae by use of fastidious broth (FB) was evaluated. FB was found to be able to support the growth of all N. gonorrhoeae strains tested in this study without a rapid decrease in the viable count after exponential growth. After 24 h of incubation at 35 degrees C with 5% CO(2), viable counts of all strains reached over 10(8) CFU/ml in FB. Similar growth of the wild-type strain and its target-altered quinolone-resistant derivatives was observed. The susceptibilities of laboratory-adapted strains and clinical isolates to quinolones were tested by the microdilution method using FB. The MICs determined by microdilution were not significantly different from those determined by the agar dilution method recommended by the CLSI (formerly National Committee for Clinical Laboratory Standards). Moreover, the concentration-dependent time-kill of quinolones such as gatifloxacin and ciprofloxacin was observed in FB. At 2 to 4 times the MIC, gatifloxacin and ciprofloxacin were predominantly bactericidal against N. gonorrhoeae WHO A. At the MIC, the activities of both quinolones ranged from bactericidal to bacteriostatic. At 0.25 to 0.5 times the MIC, gonococcal growth was comparable to that of the growth control. These results suggest that the cultivation of N. gonorrhoeae by use of FB may be useful for evaluation of the antibacterial effects of quinolones.

Fluoroquinolone-resistant Neisseria gonorrhoeae: the inevitable epidemic

The worldwide incidence of fluoroquinolone-resistant Neisseria gonorrhoeae has increased dramatically in the last few years. Single doses of fluoroquinolones can no longer be used to treat N gonorrhoeae infections acquired in the Far East, parts of the Middle East, the Pacific Islands, and parts of Western Europe and the United States. Although California and Hawaii account for most of the current United States cases, the increased incidence of FQR in some high-risk groups independent of geography heralds an imminent spread of drug-resistant strains throughout the rest of the population. The use of molecular tests has revolutionized the diagnostic field in STIs. The main limitation of their application in N gonorrhoeae testing has been the loss of culture specimens that allow antimicrobial sensitivity testing. New molecular methods have made it possible to detect antimicrobial resistance without the use of live organisms. These tests hold the promise of improving epidemiologic tracking of N gonorrhoeae drug resistance, leading to better patient management at the local level. The loss of fluoroquinolones limits available oral regimens to a single CDC-recommended antibiotic, cefixime. Oral, inexpensive, single-dose alternatives are needed to ensure continued therapeutic success.

Use of applied biosystems 7900HT sequence detection system and Taqman assay for detection of quinolone-resistant Neisseria gonorrhoeae

Mutations in quinolone resistance-determining regions (QRDRs) have been associated with quinolone-resistant Neisseria gonorrhoeae (QRNG). Since diagnostic nucleic acid amplification tests for gonococci are now in frequent use, molecular detection of QRNG could facilitate surveillance in the absence of culture. Here we describe a real-time molecular assay for detecting QRDR mutations in gonococci.

Remarkable increase in central Japan in 2001-2002 of Neisseria gonorrhoeae isolates with decreased susceptibility to penicillin, tetracycline, oral cephalosporins, and fluoroquinolones

Four hundred sixty-two clinical isolates of Neisseria gonorrhoeae recovered from 1999 through 2002 in central Japan were examined for MICs of antimicrobial agents. The majority was sensitive to ceftriaxone and spectinomycin, but a remarkable increase in isolates with decreased susceptibility to penicillin, tetracycline, oral cephalosporins, and fluoroquinolones was observed from 2001 through 2002.

The use of fluoroquinolones in gonorrhoea: the increasing problem of resistance

The recent re-emergence of gonorrhoea in developed countries has been accompanied by the rise and spread of gonococcal resistance to the fluoroquinolones. In the 1980s fluoroquinolones were considered an important addition to the arsenal of agents used to treat gonorrhoea. They proved to be excellent drugs for this indication, including infections caused by penicillinase-producing and tetracycline-resistant strains of Neisseria gonorrhoeae. However, as gonococci have a well-recognised potential to develop resistance to antibiotics, the first reports of reduced susceptibility to fluoroquinolones appeared a few years after their introduction. Gonococcal resistance to fluoroquinolones is now well-established in the Far East, from where it has spread to Australia, Hawaii, California and Europe. In Africa and Latin America, gonococci continue to be susceptible to fluoroquinolones.

Treatment of uncomplicated gonococcal urethritis by double-dosing of 200 mg cefixime at a 6-h interval

The efficacy of antimicrobial regimens for the treatment of uncomplicated gonococcal urethritis depends partially upon the period of time (therapeutic time) during which the drug concentration in the blood after the concentration peak is greater than four times the minimum inhibitory concentration for 90% of clinical isolates of Neisseria gonorrhoeae (MIC(90)). A therapeutic time of at least 10 h is suggested as an important determinant for elimination of 95% or more of the infection. In this study, therapeutic times for a single 400-mg dose of cefixime at various MIC(90)s were calculated, and pharmacokinetic profiles of double-dosing of 200 mg cefixime at various intervals were simulated. Subsequently, a dosing interval of 6 h was tested in 6 healthy Japanese men, and then 93 Japanese men with gonococcal urethritis were treated with a regimen of two 200-mg doses of cefixime given at a 6-h interval. For a single dose of 400 mg cefixime, therapeutic times were calculated to be 12.8, 9.1, 5.4, and 1.7 h for MIC(90)s of 0.06, 0.125, 0.25, and 0.5 microg/ml, respectively. In the simulation study of double-dosing of 200 mg cefixime at a 6-h interval, the therapeutic times for the MIC(90)s of < or =0.125 microg/ml were longer than 10 h. Of the 93 patients, 68 were evaluated for microbiological outcome, and N. gonorrhoeae was eradicated in 60 (88.2%). The MIC(90) of cefixime for the 61 isolates tested was 0.125 microg/ml. All strains with MICs of < or =0.06 microg/ml were eradicated, whereas 8 of 16 strains with MICs of > or =0.125 microg/ml persisted after treatment. This regimen would not be effective against infection by strains exhibiting cefixime MIC(90)s of > or =0.125 microg/ml. For such strains, a different regimen with a higher dose of cefixime would be required.

Quinolone Resistance in Neisseria gonorrhoeae

Single-dose oral quinolones have been recommended for gonorrhea treatment since 1989. The antimicrobial resistance surveillance system has detected several outbreaks of quinolone-resistant gonococcal infections (QRNG), and sporadic treatment failures have been reported from high-incidence areas such as southeast Asia. QRNG may result from mutations that cause structural-functional changes in DNA topoisomerase (the quinolone target enzyme) or by changes in antimicrobial transport into the bacteria. QRNG has occurred sporadically in the United States, predominantly in persons with contact to persons in southeast Asia, and has typically occurred as an epiphenomenon in persons who were treated with other regimens. Nevertheless, this entity warrants close monitoring. The emergence of QRNG is probably related to antimicrobial misuse and overuse, in particular long-term suppressive or subtherapeutic doses.

Clinical perspectives on new antimicrobials: focus on fluoroquinolones

Respiratory tract infections are the most common infectious presentation in the community and hospital settings and are a major cause of morbidity and mortality worldwide. Recently, newer fluoroquinolones have been recommended for the treatment of these infections. Among them, moxifloxacin shows improved activity against gram-positive pathogens, has maintained potency against gram-negative organisms, and shows activity against atypical pathogens and anaerobes. Moxifloxacin also has excellent in vitro activity against strains resistant to penicillin, erythromycin, and other fluoroquinolones, such as levofloxacin. Moxifloxacin has demonstrated clinical efficacy rates of 90%-95% in clinical trials in community-acquired pneumonia, acute exacerbations of chronic bronchitis, and acute sinusitis. In these trials, moxifloxacin demonstrated no serious or unexpected adverse effects. Development of resistance appears to be slower for moxifloxacin than for several other fluoroquinolones, making moxifloxacin a good treatment choice. The pharmacodynamics of moxifloxacin support once-daily oral therapy of short duration, providing convenience, compliance, and safety advantages.

Single-dose gatifloxacin compared with ofloxacin for the treatment of uncomplicated gonorrhea: a randomized, double-blind, multicenter trial

BACKGROUND

Treatment of gonorrhea is complicated by widespread resistance of Neisseria gonorrhoeae to antimicrobial agents of choice, including decreased susceptibility to ciprofloxacin.

GOAL

To demonstrate the efficacy and safety of gatifloxacin, a novel 8-methoxy fluoroquinolone antibiotic, compared with ofloxacin in treating patients with uncomplicated gonococcal infection.

STUDY DESIGN

In a double-blind, randomized (2:2:1), controlled trial, 340 men and 388 women with uncomplicated gonorrhea who were 16 years or older received a single oral dose of gatifloxacin (400 mg or 600 mg) or ofloxacin (400 mg). Primary analysis of efficacy was based on bacteriologic eradication from sites of infection. Secondary analyses examined clinical response and adverse event profiles.

RESULTS

Bacteriologic eradication rates for gatifloxacin in evaluable men with urethral gonorrhea were 99% (400 mg) and 100% (600 mg) versus 100% for ofloxacin (n = 117, 122, and 55, respectively; P = ns). Eradication rates in evaluable women with endocervical gonorrhea were 99% for both 400 mg and 600 mg gatifloxacin versus 100% for ofloxacin (n = 101, 104, and 55, respectively; P = ns). Eradication rates were 100% for both rectal (n = 43) and pharyngeal (n = 31) infection across all treatment groups. All three drug regimens were well tolerated and exhibited similar clinical response profiles.

CONCLUSION

Gatifloxacin is safe and effective as a single 400-mg or 600-mg dose for the treatment of uncomplicated gonorrhea. Similar efficacy rates were observed with the 400-mg and 600-mg doses. A single 400-mg dose can be recommended for treatment of uncomplicated gonorrhea.

Concurrent gonococcal and chlamydial infection: how best to treat

Clinicians treating concurrent gonococcal and chlamydial infections have a variety of drugs to choose from. Neisseria gonorrhoeae is adept at developing resistance and the choice of antibiotic must be dictated to some extent by the patterns of resistance in the locality of the clinician. In contrast, resistance of Chlamydia trachomatis to some classes of drugs has been shown in vitro but does not appear to be clinically important at present. The success of treatment depends on patient compliance with the drug administration schedule. With these organisms, which can be carried asymptomatically, many patients are unlikely to comply with courses of antibiotics. Although single-dose therapy with azithromycin is available and established for chlamydial genital infection, it is more expensive and difficult to justify in a cash limited Healthcare system, and its efficacy for treating concurrent gonococcal infection requires further study. In patients where compliance is likely to be of concern, its use may be justified. Another major deterrent for completing antibiotic courses is the adverse effect profile. Most of the available drugs cause only minor adverse effects, in particular gastrointestinal. Ofloxacin has a better profile than doxycycline but is considerably more expensive. Newer fluoroquinolones, found to be effective in vitro, are being assessed in clinical studies. However, more evidence is required before recommending these over the tried and tested therapies.

Increasing antimicrobial resistance in STDs and the need for surveillance: Neisseria gonorrhoeae as a model

Neisseria gonorrhoeae has a rising trend of resistance against antimicrobials. Today, third generation cephalosporins are the only antibiotics for treatment of gonorrhea against which there is no resistance in gonococci. On the other hand, decreased susceptibility against this group, including ceftriaxone, has already been observed. This historically famous pathogen deserves current attention and is reviewed here with respect to its resistance mechanisms and patterns, and the problems concerning standardization of its susceptibility testing are discussed.

Antimicrobial resistance in Neisseria gonorrhoeae

Despite a declining incidence of gonorrhea in much of the industrialized world, antimicrobial resistance continues to present a challenge to the treatment of gonococcal infections. Although no clinically significant resistance to the broad-spectrum cephalosporins has been identified, fluoroquinolone-resistant gonococcal strains are now prevalent in Australia and much of the Far East. Ongoing surveillance for antimicrobial resistance is crucial to obtain the information needed to choose effective empiric therapies for gonorrhea.

Drift in susceptibility of Neisseria gonorrhoeae to ciprofloxacin and emergence of therapeutic failure

Ciprofloxacin, 500 mg, was introduced as the first-line therapy for gonorrhea at St. Mary's Hospital, London, in 1989, when a surveillance program was initiated to detect the emergence of resistance. Isolates of Neisseria gonorrhoeae from consecutive patients attending the Jefferiss Wing, Genitourinary Medicine Clinic at St. Mary's Hospital, between 1989 and 1997 have been tested for susceptibility to ciprofloxacin by using an agar dilution breakpoint technique. Isolates considered potentially resistant (MIC, >0.12 microg/ml) were further characterized by determination of the MICs of ciprofloxacin, nalidixic acid, and penicillin, auxotyped and serotyped, and screened for mutations in the DNA gyrase gene, gyrA, and the topoisomerase IV gene, parC. A total of 4,875 isolates were tested. While the majority of isolates were highly susceptible (MIC, 0.12 microg/ml); all of these belonged to serogroup B, and NR/IB-1 was the most common auxotype/serovar class. The infections in 14 of the 18 patients were known to be acquired abroad, and 5 were known to result in therapeutic failure. The surveillance program has established that ciprofloxacin is still a highly effective antibiotic against N. gonorrhoeae in this population. However, it has identified a drift in susceptibility which may have resulted from increased usage of ciprofloxacin. High-level resistance has now emerged, although treatment failure is still uncommon.