High-level azithromycin resistance occurs in Neisseria gonorrhoeae as a result of a single point mutation in the 23S rRNA genes

Surveillance and molecular epidemiology of Neisseria gonorrhoeae isolates in Shenzhen, China, 2010-2017

OBJECTIVES

The development and emergence of antimicrobial resistance in Neisseria gonorrhoeae (NG) have become a major public-health problem worldwide. This study aimed to analyse the antimicrobial susceptibility and molecular characteristics of NG isolates in Shenzhen, China.

METHODS

A total of 1282 NG isolates were consecutively collected between 2010 and 2017. Patient demographic information was also collected. MICs of ceftriaxone, spectinomycin, ciprofloxacin, azithromycin and penicillin were determined by agar dilution. Isolates were genotyped using N. gonorrhoeae multi-antigen sequence typing (NG-MAST).

RESULTS

Among the isolates, 97.4% were resistant to ciprofloxacin and 68.2% to penicillin. Moreover, 5.0% showed decreased susceptibility to ceftriaxone (CRO^D) and 17.3% were resistant to azithromycin (AZM-R); 1.3% were simultaneously CRO^D and AZM-R. All isolates were susceptible to spectinomycin. Increasing ceftriaxone MICs were found from 2010 to 2017. A total of 427 sequence types (STs) and 68 genogroups were identified from 724 isolates. ST5061, ST3741 and ST1766 were observed across the study years. ST14638 (n = 3) was predominant among 32 CRO^D isolates. Prevalent STs were ST5061 (n = 6), ST1866 (n = 5) and ST11133 (n = 5) among 96 AZM-R isolates.

CONCLUSIONS

A high prevalence of isolates resistant to ciprofloxacin and penicillin was found in this study. Azithromycin, one antimicrobial of dual antimicrobial therapy recommended by the WHO, showed a high prevalence of resistance. The other, ceftriaxone, can be used continuously in this region owing to lower resistance levels. However, the emergence of CRO^D and decreasing susceptibility to ceftriaxone indicate that continuous antimicrobial resistance surveillance is essential.

Azithromycin resistant gonococci: a literature review

OBJECTIVE

Gonorrhea is the second most common sexually transmitted bacterial infection (STI) next to Chlamydia. Untreated cases could results in major complications like pelvic inflammatory disease (PID), ectopic pregnancy, infertility, miscarriage, fetal death and congenital infections. Gonorrhea has been treated with antibiotics for more than eight decades. However, the emergence and spread of antimicrobial resistance (AMR) in gonococcus seriously compromises the management of the disease. The aim of this review was to describe the current developments in the field of azithromycin resistant gonococci.

METHODS

Literatures published in English in the last 10 years were retrieved from PubMed, SCOPUS, Google scholar, Cochrane library and the Google databases using relevant searching terms.

RESULTS

Gonococcus is capable of using a number of strategies to confer resistance as the bacterium has an extraordinary capacity to alter its genome. So far the accumulated data on the field showed that the world is heading towards a pandemic of extensively drug-resistant (XDR) gonococcus which is now seems to be evolving into a true "superbug". Hence, in the near future gonorrhea may become untreatable on the international basis unless new drugs become available. An antibiotic resistance in gonococcus has been noted beginning in 1940s against sulfonamides. Since then, resistance has rapidly emerged to penicillins, tetracyclines, macrolides, fluoroquinolones, and cephalosporins. Currently, in most nations, the injectable extended-spectrum cephalosporin (ESC), i.e. ceftriaxone based therapy is the only remaining option for gonorrhea. Based on the WHO and the US-CDC recommendations, countries are increasingly using a combination of cephalosporin and azithromycin for the treatment of gonorrhoea. Azithromycin revolutionized gonoccocal therapy as it shortened treatment time by more than half from 7 to 14 days and improved patient compliance due to high tissue levels and long half-life. However, constantly emerging reports from different parts of the globe showed that N. gonorrhoeae is developing significant level of resistance against azithromycin, and so far more than 33% level of resistance was reported. Two strategies have been commonly implicated in gonococcal resistance against azithromycin: over expression of an efflux pump (due to mutations at mtrR coding region) and decreased antimicrobial affinity (due to mutations in genes encoding the 23S ribosomal subunit).

CONCLUSIONS

With no alternative antimicrobial treatment options for gonorrhoea and only a few new drugs in the development pipeline, it is necessary to monitor drug resistance and optimize treatment regimens regularly. Moreover, investigations for novel drugs should be wired.

Optimising treatments for sexually transmitted infections: surveillance, pharmacokinetics and pharmacodynamics, therapeutic strategies, and molecular resistance prediction

Progressive antimicrobial resistance in Neisseria gonorrhoeae, Mycoplasma genitalium, and Trichomonas vaginalis has created a pressing need for treatment optimisations for sexually transmitted infections (STIs). In this Review, we aim to highlight urgent needs in global STI management, including: (1) improved surveillance to monitor antimicrobial resistance and clinical outcomes; (2) systematic pharmacokinetic and pharmacodynamic evaluations to ensure resistance suppression and bacterial eradication at all sites of infection; (3) development of novel, affordable antimicrobials; and (4) advancements in new molecular and point-of-care tests to detect antimicrobial resistance determinants. Antimicrobial resistance among STIs is a global public health crisis. Continuous efforts to develop novel antimicrobials will be essential, in addition to other public health interventions to reduce the global STI burden. Apart from prevention through safer sexual practices, the development of STI vaccines to prevent transmission is a crucial research priority.

Persistence Dynamics of Antimicrobial-Resistant Neisseria in the Pharynx of Rhesus Macaques

Pharyngeal infections by Neisseria gonorrhoeae are often asymptomatic, making them difficult to treat. However, in vivo animal modeling of human pharyngeal infections by pathogenic Neisseria species is challenging due to numerous host tropism barriers. We have relied on rhesus macaques to investigate pharyngeal persistence of naturally occurring Neisseria species in response to antibiotics. These species include Neisseria mucosa, Neisseria oralis, and a species unique to macaques. Four animals previously treated intramuscularly with the fluoroquinolone enrofloxacin for 2 weeks were monitored for persistence of their preexisting Neisseria populations for a period of 10 weeks. Enrofloxacin exposure did not eliminate preexisting flora from two of the four animals. Characterization of a collection of macaque Neisseria isolates supported the hypothesis that pharyngeal persistence was linked to reduced enrofloxacin susceptibility conferred by mutations in either gyrA or parC Interestingly, we observed a change in neisserial population dynamics for several weeks following enrofloxacin exposure. Enrofloxacin appeared to promote competition between strains for dominance in the pharyngeal niche. Specifically, following enrofloxacin treatment, strains bearing single gyrA mutations and low MICs persisted long-term. In contrast, strains with both gyrA and parC mutations and high MICs became culturally undetectable, consistent with the hypothesis that they were less fit. Our study has provided insight into pharyngeal persistence dynamics of Neisseria species bearing fluoroquinolone resistance determinants. The rhesus macaque provides a valuable host animal that may be used in the future to simulate treatment failures associated with the presence of antimicrobial-resistant Neisseria spp. in the human pharynx.

Genetic relatedness of ceftriaxone-resistant and high-level azithromycin resistant Neisseria gonorrhoeae cases, United Kingdom and Australia, February to April 2018

Between February and April 2018, three ceftriaxone-resistant and high-level azithromycin-resistant Neisseria gonorrhoeae cases were identified; one in the United Kingdom and two in Australia. Whole genome sequencing was used to show that the isolates from these cases belong to a single gonococcal clone, which we name the A2543 clone.

Antimicrobial Resistance of Neisseria Gonorrhoeae in a Newly Implemented Surveillance Program in Uganda: Surveillance Report

BACKGROUND

Neisseria gonorrhoeae (commonly known as gonorrhea) has developed resistance to all first-line therapy in Southeast Asia. East Africa has historically had absent or rudimentary gonorrhea surveillance programs and, while the existence of antimicrobial-resistant gonorrhea is recognized, the extent of its resistance is largely unknown. In 2016, the World Health Organization's Enhanced Gonococcal Antimicrobial Surveillance Program (EGASP) was initiated in Uganda to monitor resistance trends.

OBJECTIVE

This study characterizes gonorrhea and antibiotic resistance in a large surveillance program of men with urethral discharge syndrome from Kampala, Uganda.

METHODS

Men attending sentinel clinics with urethritis provided demographic information, behavior data, and a urethral swab in line with the World Health Organization's EGASP protocols for culture, identification, and antibiotic-sensitivity testing using 2 methods-disk diffusion (Kirby-Bauer test) and Etest (BioMérieux Inc). A subset of samples underwent detailed antimicrobial resistance testing.

RESULTS

Of 639 samples collected from September 2016 to February 2018, 400 (62.6%) were culture-positive though 414 (64.8%) had microscopic evidence of gonorrhea. The mean age of the men from whom the samples were collected was 26.9 (SD 9.6) years and 7.2% (46/639) reported having HIV. There was high-level resistance to ciprofloxacin, tetracycline, and penicillin (greater than 90%) by Kirby-Bauer disk diffusion and 2.1% (4/188) had reduced azithromycin sensitivity by Etest. Of the early isolates that underwent detailed characterization, 60.3% (70/116) were culture-positive, 94% (66/69) isolates were either ciprofloxacin-resistant or ciprofloxacin-intermediate by Etest, 96% (65/68) were azithromycin-sensitive, and 96% (66/69) were gentamicin-sensitive. Resistance profiles were comparable between methods except for ceftriaxone (disk diffusion: 68/69, 99%; Etest: 67/69, 97%) and for gentamicin (disk diffusion: 2/8, 25%; Etest: 66/69, 96%) sensitivity.

CONCLUSIONS

This is the first report from a systematic gonorrhea surveillance program in Uganda. Findings demonstrated resistance or increased minimum inhibitory concentration to all key antigonococcal antibiotics. There was evidence of poor antibiotic stewardship, near-universal resistance to several antibiotics, and emerging resistance to others. Individuals in the population sampled were at exceptionally high risk of STI and HIV infection requiring intervention. Ongoing surveillance efforts to develop interventions to curtail antimicrobial-resistant gonorrhea are needed.

Neisseria gonorrhoeae 23S rRNA A2059G mutation is the only determinant necessary for high-level azithromycin resistance and improves in vivo biological fitness

Objectives

The global emergence of Neisseria gonorrhoeae isolates displaying high-level azithromycin resistance is a major concern for the currently recommended azithromycin/ceftriaxone dual therapy. N. gonorrhoeae high-level azithromycin resistance has been associated with an A2059G mutation in 23S rRNA. Here we investigated the specific contribution of this 23S rRNA A2059G mutation to high-level azithromycin resistance and its impact on biological fitness.

Methods

A2059G/G2059A alleles were specifically cloned into all four genomic copies of 23S rDNA of an azithromycin-susceptible isolate and a high-level azithromycin-resistant isolate. WT and mutant strains were subsequently investigated for azithromycin susceptibility using the agar dilution method. In addition, their biological fitness was studied by comparative liquid growth in the presence of hydrophobic and amphipathic compounds, by competition assays in a mouse vaginal tract infection model and by competition assays for invasion and intracellular survival.

Results

Azithromycin susceptibility analyses showed that the 23S rRNA A2059G mutation is the only genetic determinant required for N. gonorrhoeae to display the high-level azithromycin resistance phenotype. Further analysis of biological fitness showed that strains containing 2059G outcompeted isogenic strains containing 2059A for colonization in the mouse vaginal tract infection model and for invasion of HeLa cervical epithelial cells. Furthermore, the A2059G mutation enhanced growth in the presence of lithocholic acid or Triton X-100.

Conclusions

Our findings that the 23S rRNA A2059G mutation is sufficient for high-level azithromycin resistance and that this mutation generally enhanced the biological fitness of N. gonorrhoeae have important implications for the currently recommended treatment policies and antimicrobial stewardship programmes.

Genomic Characterization of Neisseria gonorrhoeae Strains from 2016 U.S. Sentinel Surveillance Displaying Reduced Susceptibility to Azithromycin

In 2016, the proportion of Neisseria gonorrhoeae isolates with reduced susceptibility to azithromycin rose to 3.6%. A phylogenetic analysis of 334 N. gonorrhoeae isolates collected in 2016 revealed a single, geographically diverse lineage of isolates with MICs of 2 to 16 μg/ml that carried a mosaic-like mtr locus, whereas the majority of isolates with MICs of ≥16 μg/ml appeared sporadically and carried 23S rRNA mutations. Continued molecular surveillance of N. gonorrhoeae isolates will identify new resistance mechanisms.

Evidence of Recent Genomic Evolution in Gonococcal Strains With Decreased Susceptibility to Cephalosporins or Azithromycin in the United States, 2014-2016

BACKGROUND

Given the lack of new antimicrobials or a vaccine, understanding the evolutionary dynamics of Neisseria gonorrhoeae is a significant public and global health priority. We investigated the emergence and spread of gonococcal strains with decreased susceptibility to cephalosporins and azithromycin using detailed genomic analyses of gonococcal isolates collected in the United States, 2014-2016.

METHODS

We sequenced genomes of 649 isolates collected through the Gonococcal Isolate Surveillance Project. We examined the genetic relatedness of isolates and assessed associations between clades and various genotypic and phenotypic combinations.

RESULTS

We identified a large and clonal lineage of strains (MLST ST9363) associated with elevated azithromycin minimum inhibitory concentration (AZIem), characterized by a mosaic mtr locus (C substitution in the mtrR promoter, mosaic mtrR and mtrD). Mutations in 23S rRNA were sporadically distributed among AZIem strains. Another clonal group (MLST ST1901) possessed 7 unique PBP2 patterns, and it shared common mutations in other genes associated with cephalosporin resistance.

CONCLUSIONS

Whole-genome sequencing methods can enhance monitoring of antimicrobial resistant gonococcal strains by identifying gonococcal populations containing mutations of concern. These methods could inform the development of point-of-care diagnostic tests designed to determine the specific antibiotic susceptibility profile of a gonococcal infection in a patient.

Equations To Predict Antimicrobial MICs in Neisseria gonorrhoeae Using Molecular Antimicrobial Resistance Determinants

The emergence of Neisseria gonorrhoeae strains that are resistant to azithromycin and extended-spectrum cephalosporins represents a public health threat, that of untreatable gonorrhea infections. Multivariate regression modeling was used to determine the contributions of molecular antimicrobial resistance determinants to the overall antimicrobial MICs for ceftriaxone, cefixime, azithromycin, tetracycline, ciprofloxacin, and penicillin. A training data set consisting of 1,280 N. gonorrhoeae strains was used to generate regression equations which were then applied to validation data sets of Canadian (n = 1,095) and international (n = 431) strains. The predicted MICs for extended-spectrum cephalosporins (ceftriaxone and cefixime) were fully explained by 5 amino acid substitutions in PenA, A311V, A501P/T/V, N513Y, A517G, and G543S; the presence of a disrupted mtrR promoter; and the PorB G120 and PonA L421P mutations. The correlation of predicted MICs within one doubling dilution to phenotypically determined MICs of the Canadian validation data set was 95.0% for ceftriaxone, 95.6% for cefixime, 91.4% for azithromycin, 98.2% for tetracycline, 90.4% for ciprofloxacin, and 92.3% for penicillin, with an overall sensitivity of 99.9% and specificity of 97.1%. The correlations of predicted MIC values to the phenotypically determined MICs were similar to those from phenotype MIC-only comparison studies. The ability to acquire detailed antimicrobial resistance information directly from molecular data will facilitate the transition to whole-genome sequencing analysis from phenotypic testing and can fill the surveillance gap in an era of increased reliance on nucleic acid assay testing (NAAT) diagnostics to better monitor the dynamics of N. gonorrhoeae.

Characterization of antimicrobial resistance genes from Neisseria gonorrhoeae positive remnant Aptima urine specimens

Aim: To ascertain the antimicrobial resistance and strain types (STs) of Neisseria gonorrhoeae from 50 remnant Aptima urine specimens using molecular methods. Methods: Mutations predictive of resistance to six antibiotics were identified in eight genes. STs were determined using NG-MAST and NG-STAR. Results: All eight antimicrobial resistance genes could be characterized in 36 specimens. A total of 17 specimens were predicted to be susceptible to all antibiotics, including ceftriaxone. Decreased susceptibility to cefixime and ciprofloxacin resistance was predicted in 11 specimens (PBP2 type 34.001). Overall, 38/50 specimens were predicted to be ciprofloxacin susceptible; three were azithromycin resistant. Nineteen NG-MAST and 21 NG-STAR STs were noted. Conclusion: Molecular analysis of remnant Aptima specimens enabled the prediction of emerging gonococcal cefixime and azithromycin resistance which would otherwise have been undetected.

Increasing prevalence of Neisseria gonorrhoeae with decreased susceptibility to ceftriaxone and resistance to azithromycin in Hangzhou, China (2015-17)

Objectives

Development of resistance in Neisseria gonorrhoeae to ceftriaxone monotherapy or ceftriaxone plus azithromycin dual therapy is a global public health concern. The aim of this study was to analyse the trend in antimicrobial resistance in Hangzhou, China, over the period 2015-17.

Methods

In total, 379 clinical isolates were collected from seven hospitals and antimicrobial susceptibility was determined using the agar dilution method. Isolates showing resistance to ceftriaxone, azithromycin or cefixime were analysed for the presence of resistance determinants. STs were determined with the N. gonorrhoeae multiantigen sequence typing (NG-MAST) method and phylogenetic analysis and strain clustering was determined using porB and tbpB sequences.

Results

Ceftriaxone resistance, decreased susceptibility to ceftriaxone and azithromycin resistance were observed in 3%, 17% and 21% of the isolates, respectively. This resulted in 5% of the isolates showing both decreased susceptibility to ceftriaxone and azithromycin resistance. Importantly, resistance levels to ceftriaxone and azithromycin increased over the study period, resulting in 5% ceftriaxone resistance, 27% decreased susceptibility to ceftriaxone and 35% azithromycin resistance in 2017 and 11% of the isolates showing both decreased susceptibility to ceftriaxone and azithromycin resistance. Phylogenetic and cluster analysis showed the emergence and expansion in 2017 of a clonally related cluster containing strains with high abundance of decreased susceptibility to ceftriaxone and/or cefixime, which was related to the presence of the mosaic penA allele X. Co-resistance to azithromycin was also observed in this cluster.

Conclusions

Our findings have major implications for the future reliability of ceftriaxone monotherapy and ceftriaxone plus azithromycin dual therapy in China.

Emergence and Spread of Neisseria gonorrhoeae Strains with High-Level Resistance to Azithromycin in Taiwan from 2001 to 2018

A total of 598 Neisseria gonorrhoeae isolates obtained from patients in Taiwan from 2001 to 2018 were evaluated. The MICs of ceftriaxone (CRO) and azithromycin (AZM) against the isolates were determined by the agar dilution method. N. gonorrhoeae isolates with AZM MICs of ≥1 μg/ml were identified and characterized by the presence of AZM resistance determinants. For high-level AZM-resistant (AZM-HLR) isolates (MIC ≥ 256 μg/ml), genotyping was performed using multilocus sequence typing (MLST) and N. gonorrhoeae multiantigen sequence typing (NG-MAST). Among the N. gonorrhoeae isolates studied, 8.7% (52/598) exhibited AZM MICs of ≥1 μg/ml. Thirteen of the 52 isolates contained A2059G (23S rRNA NG-STAR type 1) or C2611T (23S rRNA NG-STAR type 2) mutations. The prevalence of the A2059G mutation was higher in AZM-HLR isolates (P < 0.001). The -35A deletion in the promoter region of the mtrR gene did not differ between AZM-HLR isolates (100%, 10/10) and the isolates with AZM MICs of 1 μg/ml to 64 μg/ml (95.2%, 40/42) (P = 1.000). The presence of mutations in the mtrR coding region was significantly different between these two groups at 90% (9/10) and 26.2% (11/42), respectively (P < 0.001). The AZM-HLR isolates, all carrying four mutated A2059G alleles, a -35A deletion, and G45D, were classified as MLST 12039/10899 and NG-MAST 1866/16497. In conclusion, Taiwan is among the countries reporting gonococci with high-level resistance to AZM so that a single dose of 1 g ceftriaxone intramuscularly as the first choice for management of N. gonorrhoeae infection should be evaluated.

Impact of Species Diversity on the Design of RNA-Based Diagnostics for Antibiotic Resistance in Neisseria gonorrhoeae

Quantitative assessment of antibiotic-responsive RNA transcripts holds promise for a rapid point-of-care (POC) diagnostic tool for antimicrobial susceptibility testing. These assays aim to distinguish susceptible and resistant isolates by transcriptional differences upon drug exposure. However, an often-overlooked dimension of designing these tests is that the genetic diversity within a species may yield differential transcriptional regulation independent of resistance phenotype. Here, we use a phylogenetically diverse panel of Neisseria gonorrhoeae and transcriptome profiling coupled with reverse transcription-quantitative PCR to test this hypothesis, to identify azithromycin responsive transcripts and evaluate their potential diagnostic value, and to evaluate previously reported diagnostic markers for ciprofloxacin resistance (porB and rpmB). Transcriptome profiling confirmed evidence of genetic distance and population structure impacting transcriptional response to azithromycin. Taking this into account, we found azithromycin-responsive transcripts overrepresented in susceptible strains compared to resistant strains and selected four candidate diagnostic transcripts (rpsO, rplN, omp3, and NGO1079) that were the most significantly differentially regulated between phenotypes across drug exposure. RNA signatures for these markers categorically predicted resistance in 19/20 cases, with the one incorrect categorical assignment for an isolate at the threshold of reduced susceptibility. Finally, we found that porB and rpmB expression were not uniformly diagnostic of ciprofloxacin resistance in a panel of isolates with unbiased phylogenetic sampling. Overall, our results suggest that RNA signatures as a diagnostic tool are promising for future POC diagnostics; however, development and testing should consider representative genetic diversity of the target pathogen.

Genomic Characterization of Gonococci from Different Anatomic Sites, Italy, 2007-2014

In recent decades, Neisseria gonorrhoeae has developed resistance to several antimicrobial classes. Molecular epidemiology approaches are useful for detecting emerging, often resistant, gonococcal clones. In this study, 67 N. gonorrhoeae isolates from different anatomic sites, collected over 8 years in Italy, were analyzed by whole genome sequencing (WGS). WGS was performed using the Illumina NextSeq 500 platform. Phylogenetic analysis was based on core single nucleotide polymorphism (SNP) and core genome multilocus sequence typing (cgMLST). N. gonorrhoeae multi-antigen sequence typing (NG-MAST), MLST, and N. gonorrhoeae sequence typing for antimicrobial resistance (NG-STAR) were carried out in silico using WGS data. Antimicrobial susceptibility against a four-drug panel was evaluated using a gradient diffusion method. Overall, gonococci clustered in accordance with NG-MAST, MLST, NG-STAR, and antimicrobials susceptibility profiles, but not with the site of isolation, HIV status, and patient sexual orientation. Phylogenetic analysis identified nine clades: two of them were the predominant and including gonococci of G1407 and G2400 genogroups.

Neisseria gonorrhoeae ciprofloxacin-resistant strains were associated with Chlamydia trachomatis coinfection

Aim: This study aims to characterize circulating strains to predict their relationship with sexually transmitted microorganisms, Chlamydia trachomatis, HIV, HCV, Treponema pallidum, HPV, Mycoplasmas, in an Italian multiethnic area, which has revealed a recent increase of Neisseria gonorrhoeae first-line antibiotic resistance. Materials & methods: We performed N. gonorrhoeae multiantigen sequence typing and the N. gonorrhoeae sequence typing for antimicrobial resistance. Results: We identified mutations in genes conferring resistance to cephalosporins, macrolides, fluoroquinolones through por and tbpB loci, and we reported new combinations of already known alleles. N. gonorrhoeae resistance to ciprofloxacin was associated with C. trachomatis coinfection. Conclusion: This study's data proved the utility of a routine N. gonorrhoeae molecular characterization to monitor the evolution of antibiotic resistance and to detect the most effective clinical treatment.

Construction and optimization of a 'NG Morbidostat' - An automated continuous-culture device for studying the pathways towards antibiotic resistance in Neisseria gonorrhoeae

To obtain a detailed picture of the dynamics of antibiotic resistance development in Neisseria gonorrhoeae, we built a morbidostat according to the protocol of Toprak et al., adjusted to the specific characteristics required for the growth of N. gonorrhoeae. In this article we describe the adaptations, specifications and the difficulties we encountered during the construction and optimization of the NG morbidostat. As a proof of concept, we conducted a morbidostat experiment by increasing concentrations of azithromycin in response to bacterial growth. We started the experiment with two N. gonorrhoeae reference strains WHO-F and WHO-X. These strains were grown in 12 mL GC Broth supplemented with IsoVitaleX™ (1%) and vancomycin, colistin, nystatin, trimethoprim (VCNT) selective supplement for 30 days in a 6% CO ₂ environment at 36°C. Samples of the cultures were taken 2-3 times a week and minimal inhibitory concentrations (MICs) of azithromycin were determined using E-test. The initial MICs of WHO-F and WHO-X were 0.125 µg/mL and 0.25 µg/mL, respectively. In less than 30 days, we were able to induce high level azithromycin resistance in N. gonorrhoeae, with a 750 and 1000 fold increase in MIC for WHO-F and WHO-X, respectively.

Construction and optimization of a 'NG Morbidostat' - An automated continuous-culture device for studying the pathways towards antibiotic resistance in Neisseria gonorrhoeae

To obtain a detailed picture of the dynamics of antibiotic resistance development in Neisseria gonorrhoeae, we built a morbidostat according to the protocol of Toprak et al., adjusted to the specific characteristics required for the growth of N. gonorrhoeae. In this article we describe the adaptations, specifications and the difficulties we encountered during the construction and optimization of the NG morbidostat. As a proof of concept, we conducted a morbidostat experiment by increasing concentrations of azithromycin in response to bacterial growth. We started the experiment with two N. gonorrhoeae reference strains WHO-F and WHO-X. These strains were grown in 12 mL GC Broth supplemented with IsoVitaleX™ (1%) and vancomycin, colistin, nystatin, trimethoprim (VCNT) selective supplement for 30 days in a 6% CO 2 environment at 36°C. Samples of the cultures were taken 2-3 times a week and minimal inhibitory concentrations (MICs) of azithromycin were determined using E-test. The initial MICs of WHO-F and WHO-X were 0.125 µg/mL and 0.25 µg/mL, respectively. In less than 30 days, we were able to induce high level azithromycin resistance in N. gonorrhoeae, with a 750 and 1000 fold increase in MIC for WHO-F and WHO-X, respectively.

Emergence of Neisseria gonorrhoeae Strains Harboring a Novel Combination of Azithromycin-Attenuating Mutations

The nimbleness of Neisseria gonorrhoeae to evade the effect of antibiotics has perpetuated the fight against antibiotic-resistant gonorrhea for more than 80 years. The ability to develop resistance to antibiotics is attributable to its indiscriminate nature in accepting and integrating exogenous DNA into its genome. Here, we provide data demonstrating a novel combination of the 23S rRNA A2059G mutation with a mosaic-multiple transferable resistance (mosaic-mtr) locus haplotype in 14 N. gonorrhoeae isolates with high-level azithromycin MICs (≥256 μg/ml), a combination that may confer more fitness than in previously identified isolates with high-level azithromycin resistance. To our knowledge, this is the first description of N. gonorrhoeae strains harboring this novel combination of resistance determinants. These strains were isolated at two independent jurisdictions participating in the Gonococcal Isolate Surveillance Project (GISP) and in the Strengthening the U.S. Response to Resistant Gonorrhea (SURRG) project. The data suggest that the genome of N. gonorrhoeae continues to shuffle its genetic material. These findings further illuminate the genomic plasticity of N. gonorrhoeae, which allows this pathogen to develop mutations to escape the inhibitory effects of antibiotics.

Antimicrobial Resistance in Neisseria gonorrhoeae: Proceedings of the STAR Sexually Transmitted Infection-Clinical Trial Group Programmatic Meeting

The goal of the Sexually Transmitted Infection Clinical Trial Group's Antimicrobial Resistance (AMR) in Neisseria gonorrhoeae (NG) meeting was to assemble experts from academia, government, nonprofit and industry to discuss the current state of research, gaps and challenges in research and technology and priorities and new directions to address the continued emergence of multidrug-resistant NG infections. Topics discussed at the meeting, which will be the focus of this article, include AMR NG global surveillance initiatives, the use of whole genome sequencing and bioinformatics to understand mutations associated with AMR, mechanisms of AMR, and novel antibiotics, vaccines and other methods to treat AMR NG. Key points highlighted during the meeting include: (i) US and International surveillance programs to understand AMR in NG; (ii) the US National Strategy for combating antimicrobial-resistant bacteria; (iii) surveillance needs, challenges, and novel technologies; (iv) plasmid-mediated and chromosomally mediated mechanisms of AMR in NG; (v) novel therapeutic (eg, sialic acid analogs, factor H [FH]/Fc fusion molecule, monoclonal antibodies, topoisomerase inhibitors, fluoroketolides, LpxC inhibitors) and preventative (eg, peptide mimic) strategies to combat infection. The way forward will require renewed political will, new funding initiatives, and collaborations across academic and commercial research and public health programs.

Genomic epidemiology and antimicrobial resistance of Neisseria gonorrhoeae in New Zealand

Background

Antimicrobial-resistant Neisseria gonorrhoeae is a major threat to public health. No studies to date have examined the genomic epidemiology of gonorrhoea in the Western Pacific Region, where the incidence of gonorrhoea is particularly high.

Methods

A population-level study of N. gonorrhoeae in New Zealand (October 2014 to May 2015). Comprehensive susceptibility testing and WGS data were obtained for 398 isolates. Relatedness was inferred using phylogenetic trees, and pairwise core SNPs. Mutations and genes known to be associated with resistance were identified, and correlated with phenotype.

Results

Eleven clusters were identified. In six of these clusters, >25% of isolates were from females, while in eight of them, >15% of isolates were from females. Drug resistance was common; 98%, 32% and 68% of isolates were non-susceptible to penicillin, ciprofloxacin and tetracycline, respectively. Elevated MICs to extended-spectrum cephalosporins (ESCs) were observed in 3.5% of isolates (cefixime MICs ≥ 0.12 mg/L, ceftriaxone MICs ≥ 0.06 mg/L). Only nine isolates had penA XXXIV genotypes, three of which had decreased susceptibility to ESCs (MIC = 0.12 mg/L). Azithromycin non-susceptibility was identified in 43 isolates (10.8%); two of these isolates had 23S mutations (C2611T, 4/4 alleles), while all had mutations in mtrR or its promoter.

Conclusions

The high proportion of females in clusters suggests transmission is not exclusively among MSM in New Zealand; re-assessment of risk factors for transmission may be warranted in this context. As elevated MICs of ESCs and/or azithromycin were found in closely related strains, targeted public health interventions to halt transmission are urgently needed.

A Comparison of Real-Time Polymerase Chain Reaction Assays for the Detection of Antimicrobial Resistance Markers and Sequence Typing From Clinical Nucleic Acid Amplification Test Samples and Matched Neisseria gonorrhoeae Culture

Real-time polymerase chain reaction (PCR) assays to detect antimicrobial resistance-associated mutations were tested on Neisseria gonorrhoeae-positive clinical samples with matched isolates. Of the nucleic acid amplification tests/cultures, 87.7% (64/73), 98.6% (72/73), and 98.4% (62/63) predicted cephalosporin, ciprofloxacin, and azithromycin susceptibilities, respectively. N. gonorrhoeae multiantigen sequence type was correctly predicted for 98.7% (79/80), and 13 of 58 N. gonorrhoeae-negative specimens showed false-positive results.

Evidence for Clonally Associated Increasing Rates of Azithromycin Resistant Neisseria gonorrhoeae in Rio de Janeiro, Brazil

Azithromycin is one of the drugs used in the combined therapy for syndromic treatment of gonorrhoea in many countries, including Brazil. Our research group, which receives isolates from clinical laboratories since 2006, has detected, after 2016, a tendency of rising rates of azithromycin resistance, with isolates showing higher minimal inhibitory concentrations (MICs) than those previously reported in this country. In this study, we report the susceptibility to azithromycin of 93 N. gonorrhoeae isolates obtained between 2014 and 2017. Strains with MIC ≥2 μg/mL were characterized according to azithromycin resistance mechanisms and strain typing. Results indicate that azithromycin resistance has emerged in all these years in unrelated MLST-STs, but after 2016 a clonal complex connected with ST1901 has been more frequently detected, grouping isolates with MIC varying from 2 to 64 μg/mL, with DelA mutations at the mtrR promoter region associated or not with mutations at rrl alleles. High rates of azithromycin resistance may compromise the use of this drug in the combined therapy with ceftriaxone. Inclusion of Rio de Janeiro in the Brazilian gonococcal surveillance program is important to evaluate if this data indicates an epidemiological phenomenon in the country.

Evaluation of the accuracy of molecular assays targeting the mutation A2059G for detecting high-level azithromycin resistance in Neisseria gonorrhoeae: a systematic review and meta-analysis

BACKGROUND

Neisseria gonorrhoeae resistance to azithromycin has become a significant public health concern globally, and high-level azithromycin-resistant (HL-AzmR) isolates have emerged frequently. However, high-level azithromycin resistance is considered to be caused by mutated alleles of 23S rRNA gene at position 2059, and identification of HL-AzmR isolates mainly relies on agar dilution method or E-test method. This study aimed to assess the accuracy of the molecular assays targeting the mutation A2059G for identifying HL-AzmR isolates and thereby determine the association between the mutation and high-level azithromycin resistance.

METHODS

Two researchers independently searched six databases to identify studies published from the launch of each database to October 15, 2017. The fixed effects model was used to estimate the pooled sensitivity rate, specificity rate, positive predictive value (PPV), and negative predictive value (NPV). Summary receiver operating characteristic curves were generated, and the area under the curve (AUC) was determined to estimate the overall performance of the assays. The Deeks' test was conducted to evaluate potential publication bias.

RESULTS

Ten relevant studies were included in the meta-analysis to assess the synthetic accuracy of the molecular assays. The molecular assays had the synthetic sensitivity rate of 97.8% and the synthetic specificity rate of 99.1%. And the aggregated PPV and NPV were 96.4% and 99.5%, respectively. AUC was 0.99, suggesting a close relation existing between the mutation A2059G and high-level azithromycin resistance. This indicated that the molecular assays targeting the mutation A2059G have relatively high overall accuracy for identifying HL-AzmR N. gonor-rhoeae isolates. Publication bias was statistically significant.

CONCLUSION

The mutation A2059G is the critical factor causing high-level azithromycin resistance. Hence, molecular methods are recommended to be put into clinical practice by commercialization, which will assist clinicians to prescribe more precisely.

Mismatch Amplification Mutation Assay-Based Real-Time PCR for Rapid Detection of Neisseria gonorrhoeae and Antimicrobial Resistance Determinants in Clinical Specimens

Molecular methods are often used for Neisseria gonorrhoeae detection, but complete definition of antimicrobial resistance (AMR) patterns still requires phenotypic tests. We developed an assay that both identifies N. gonorrhoeae and detects AMR determinants in clinical specimens.

Molecular methods are often used for Neisseria gonorrhoeae detection, but complete definition of antimicrobial resistance (AMR) patterns still requires phenotypic tests. We developed an assay that both identifies N. gonorrhoeae and detects AMR determinants in clinical specimens. We designed a mismatch amplification mutation assay (MAMA)-based SYBR green real-time PCR targeting one N. gonorrhoeae-specific region (opa); mosaic penA alleles (Asp345 deletion [Asp345del], Gly545Ser) associated with decreased susceptibility to cephalosporins; and alterations conferring resistance to ciprofloxacin (GyrA Ser91Phe), azithromycin (23S rRNA A2059G and C2611T), and spectinomycin (16S rRNA C1192T). We applied the real-time PCR to 489 clinical specimens, of which 94 had paired culture isolates, and evaluated its performance by comparison with the performance of commercial diagnostic molecular and phenotypic tests. Our assay exhibited a sensitivity/specificity of 93%/100%, 96%/85%, 90%/91%, 100%/100%, and 100%/90% for the detection of N. gonorrhoeae directly from urethral, rectal, pharyngeal, cervical, and vaginal samples, respectively. The MAMA strategy allowed the detection of AMR mutations by comparing cycle threshold values with the results of the reference opa reaction. The method accurately predicted the phenotype of resistance to four antibiotic classes, as determined by comparison with the MIC values obtained from 94 paired cultures (sensitivity/specificity for cephalosporins, azithromycin, ciprofloxacin, and spectinomycin resistance, 100%/95%, 100%/100%, 100%/100%, and not applicable [NA]/100%, respectively, in genital specimens and NA/72%, NA/98%, 100%/97%, and NA/96%, respectively, in extragenital specimens). False-positive results, particularly for the penA Asp345del reaction, were observed predominantly in pharyngeal specimens. Our real-time PCR assay is a promising rapid method to identify N. gonorrhoeae and predict AMR directly in genital specimens, but further optimization for extragenital specimens is needed.

Azithromycin Resistance through Interspecific Acquisition of an Epistasis-Dependent Efflux Pump Component and Transcriptional Regulator in Neisseria gonorrhoeae

Mosaic interspecifically acquired alleles of the multiple transferable resistance (mtr) efflux pump operon correlate with increased resistance to azithromycin in Neisseria gonorrhoeae in epidemiological studies. However, whether and how these alleles cause resistance is unclear. Here, we use population genomics, transformations, and transcriptional analyses to dissect the relationship between variant mtr alleles and azithromycin resistance. We find that the locus encompassing the mtrR transcriptional repressor and the mtrCDE pump is a hot spot of interspecific recombination introducing alleles from Neisseria meningitidis and Neisseria lactamica into N. gonorrhoeae, with multiple rare haplotypes in linkage disequilibrium at mtrD and the mtr promoter region. Transformations demonstrate that resistance to azithromycin, as well as to other antimicrobial compounds such as polymyxin B and crystal violet, is mediated through epistasis between these two loci and that the full-length mosaic mtrD allele is required. Gene expression profiling reveals the mechanism of resistance in mosaics couples novel mtrD alleles with promoter mutations that increase expression of the pump. Overall, our results demonstrate that epistatic interactions at mtr gained from multiple neisserial species has contributed to increased gonococcal resistance to diverse antimicrobial agents.IMPORTANCENeisseria gonorrhoeae is the sexually transmitted bacterial pathogen responsible for more than 100 million cases of gonorrhea worldwide each year. The incidence of resistance to the macrolide azithromycin has increased in the past decade; however, a large proportion of the genetic basis of resistance remains unexplained. This study is the first to conclusively demonstrate the acquisition of macrolide resistance through mtr alleles from other Neisseria species, demonstrating that commensal Neisseria bacteria are a reservoir for antibiotic resistance to macrolides, extending the role of interspecies mosaicism in resistance beyond what has been previously described for cephalosporins. Ultimately, our results emphasize that future fine-mapping of genome-wide interspecies mosaicism may be valuable in understanding the pathways to antimicrobial resistance. Our results also have implications for diagnostics and public health surveillance and control, as they can be used to inform the development of sequence-based tools to monitor and control the spread of antibiotic-resistant gonorrhea.

Trends in Neisseria gonorrhoeae Antimicrobial Resistance over a Ten-Year Surveillance Period, Johannesburg, South Africa, 2008⁻2017

Background: In South Africa, sexually transmitted infections (STIs) are managed through a syndromic approach at primary healthcare centres (PHCs). Neisseria gonorrhoeae is the predominant cause of male urethritis syndrome. We describe antimicrobial resistance patterns and trends in Neisseria gonorrhoeae during a ten-year surveillance period at a large PHC in Johannesburg. Methods: Neisseria gonorrhoeae was cultured from genital discharge swab specimens obtained from consenting adult patients presenting at the Alexandra Health Centre in Johannesburg between 2008 and 2017. Isolates were tested for antimicrobial susceptibility by Etest™ (cefixime, ceftriaxone, ciprofloxacin) or agar dilution (penicillin, tetracycline, azithromycin). Results: During the period of surveillance, high-level resistance prevalence increased from 30% to 51% for penicillin (p-value for trend < 0.001), 75% to 83% for tetracycline (p-value for trend = 0.008), and 25% to 69% for ciprofloxacin (p-value for trend < 0.001). Analysis did not reveal high-level resistance to spectinomycin or a minimum inhibitory concentration (MIC) creep for extended-spectrum cephalosporins, and the prevalence of intermediate-resistance to azithromycin was less than 5%. Conclusions: High prevalence resistance to penicillin, tetracycline, and ciprofloxacin in N. gonorrhoeae obviates their use in future national treatment algorithms for genital discharge. It is essential to continue monitoring for emerging resistance to currently recommended antimicrobial therapy in this rapidly evolving pathogen.

Decreased Azithromycin Susceptibility of Neisseria gonorrhoeae Isolates in Patients Recently Treated with Azithromycin

Background

Increasing azithromycin usage and resistance in Neisseria gonorrhoeae threatens current dual treatment. Because antimicrobial exposure influences resistance, we analyzed the association between azithromycin exposure and decreased susceptibility of N. gonorrhoeae.

Methods

We included N. gonorrhoeae isolates of patients who visited the Amsterdam STI Clinic between 1999 and 2013 (t0), with another clinic visit in the previous 60 days (t-1). Exposure was defined as the prescription of azithromycin at t-1. Using multivariable linear regression, we assessed the association between exposure and azithromycin minimum inhibitory concentration (MIC). Whole genome sequencing (WGS) was performed to produce a phylogeny and identify multilocus sequence types (MLST), N. gonorrhoeae multiantigen sequence types (NG-MAST), and molecular markers of azithromycin resistance.

Results

We included 323 isolates; 212 were unexposed to azithromycin, 14 were exposed ≤30 days, and 97 were exposed between 31 and 60 days before isolation. Mean azithromycin MIC was 0.28 mg/L (range, <0.016-24 mg/L). Linear regression adjusted for age, ethnicity, infection site, and calendar year showed a significant association between azithromycin exposure ≤30 days and MIC (β, 1.00; 95% confidence interval, 0.44-1.56; P = .002). WGS was performed on 31 isolates: 14 unexposed, 14 exposed to azithromycin ≤30 days before isolation, and 3 t-1 isolates. Exposure to azithromycin was significantly associated with A39T or G45D mtrR mutations (P = .046) but not with MLST or NG-MAST types.

Conclusions

The results suggest that frequent azithromycin use in populations at high risk of contracting N. gonorrhoeae induces an increase in MIC and may result in resistance.

Increasing Resistance to Azithromycin in Neisseria gonorrhoeae in Eastern Chinese Cities: Resistance Mechanisms and Genetic Diversity among Isolates from Nanjing

Azithromycin resistance (AZM-R) of Neisseria gonorrhoeae is emerging as a clinical and public health challenge. We determined molecular characteristics of recent AZM-R Nanjing gonococcal isolates and tracked the emergence of AZM-R isolates in eastern Chinese cities in recent years. A total of 384 N. gonorrhoeae isolates from Nanjing collected from 2013 to 2014 were tested for susceptibility to AZM and six additional antibiotics; all AZM-R strains were characterized genetically for resistance determinants by sequencing and were genotyped using N. gonorrhoeae multiantigen sequence typing (NG-MAST). Among the 384 isolates, 124 (32.3%) were AZM-R. High-level resistance (MIC, ≥256 mg/liter) was present in 10.4% (40/384) of isolates, all of which possessed the A2143G mutation in all four 23S rRNA alleles. Low- to mid-level resistance (MIC, 1 to 64 mg/liter) was present in 21.9% (84/384) of isolates, 59.5% of which possessed the C2599T mutation in all four 23S rRNA alleles. The 124 AZM-R isolates were distributed in 71 different NG-MAST sequence types (STs). ST1866 was the most prevalent type in high-level AZM-R (HL-AZM-R) isolates (45% [18/40]). This study, together with previous reports, revealed that the prevalence of AZM-R in N. gonorrhoeae isolates in certain eastern Chinese cities has risen >4-fold (7% to 32%) from 2008 to 2014. The principal mechanisms of AZM resistance in recent Nanjing isolates were A2143G mutations (high-level resistance) and C2599T mutations (low- to mid-level resistance) in the 23S rRNA alleles. Characterization of NG-MAST STs and phylogenetic analysis indicated the genetic diversity of N. gonorrhoeae in Nanjing; however, ST1866 was the dominant genotype associated with HL-AZM-R isolates.

Sustained transmission of high-level azithromycin-resistant Neisseria gonorrhoeae in England: an observational study

BACKGROUND

Between Nov 3, 2014, and Feb 24, 2017, 70 cases of high-level azithromycin-resistant (HL-AziR; minimum inhibitory concentration [MIC] ≥256 mg/L) Neisseria gonorrhoeae were reported from across England. Whole-genome sequencing was done to investigate this outbreak to determine whether the ongoing outbreak represented clonal spread of an HL-AziR N gonorrhoeae strain identified in Leeds. We also wanted to elucidate the molecular mechanisms of azithromycin resistance in N gonorrhoeae in the UK.

METHODS

In this observational study, whole-genome sequencing was done on the HL-AziR N gonorrhoeae isolates from England. As comparators, 110 isolates from the UK and Ireland with a range of azithromycin MICs were also sequenced, including eight isolates from Scotland with azithromycin MICs ranging from 0·12 mg/L to 1·00 mg/L that were N gonorrhoeae multi-antigen sequence type 9768 (ST9768), which was the sequence type initially responsible for the outbreak. The presence of mutations or genes associated with azithromycin resistance was also investigated.

FINDINGS

37 of the 60 HL-AziR isolates from England belonged to ST9768, and were genetically similar (mean 4·3 single-nucleotide polymorphisms). A 2059A→G mutation was detected in three or all four alleles of the 23S rRNA gene. Five susceptible ST9768 isolates had one mutated 23S rRNA allele and one low-level resistant ST9768 isolate had two mutated alleles.

INTERPRETATION

Sustained transmission of a successful HL-AziR clone was seen across England. Mutation 2059A→G was found in isolates with lower azithromycin MICs. Azithromycin exposure might have provided the selection pressure for one or two mutated copies of the 23S rRNA gene to recombine with wild-type copies, leading to three or four mutated copies and the HL-AziR phenotype. HL-AziR could emerge in isolates with low azithromycin MICs and eliminate the effectiveness of azithromycin as part of dual therapy for the treatment of gonorrhoea.

FUNDING

Public Health England.

Increases in Neisseria gonorrhoeae With Reduced Susceptibility to Azithromycin Among Men Who Have Sex With Men in Seattle, King County, Washington, 2012-2016

Background

Antimicrobial-resistant Neisseria gonorrhoeae is a major public health threat. The Centers for Disease Control and Prevention (CDC) recommends ceftriaxone 250 mg plus azithromycin (AZM) 1 g for gonorrhea treatment. Resistance to AZM could affect gonorrhea control efforts.

Methods

Using gonococcal isolates collected at the Public Health-Seattle & King County (PHSKC) Sexually Transmitted Disease (STD) Clinic from 2012 to 2016, focusing on 2014-2016, we compared cases with the CDC AZM alert value minimum inhibitory concentration (MIC) (≥2 µg/mL) to those with AZM MIC ≤1 µg/mL, antimicrobial susceptibility profiles and clinical outcomes.

Results

In 2012 and 2013, none of the 263 patients from whom we isolated N. gonorrhoeae from the urethra were infected with organisms with an AZM MIC ≥2 µg/mL. Between 2014 and 2016, 4.4% of 926 gonorrhea cases demonstrated reduced susceptibility to AZM; 93% of these cases occurred among men who have sex with men (MSM). Among MSM, 5.0% of 2014-2016 cases demonstrated reduced susceptibility to AZM. No AZM alert value isolates had concomitant cephalosporin resistance. There were 2 potential treatment failures: 1 pharyngeal infection treated with AZM 2 g alone, and 1 pharyngeal infection that persisted after study drug.

Conclusions

Among MSM with gonorrhea in Seattle, 5% have gonorrhea with reduced susceptibility to AZM. The World Health Organization recommends changing treatment guidelines when >5% of isolates are resistant to a recommended drug. The emergence of resistant AZM gonorrhea should prompt reconsideration of current treatment recommendations, and highlights the need for new therapies for gonorrhea.

Antimicrobial resistance of Neisseria gonorrhoeae in Germany: low levels of cephalosporin resistance, but high azithromycin resistance

Background

The widespread antimicrobial resistance of Neisseria gonorrhoeae is a serious problem for the treatment and control of gonorrhoea. Many of the previously effective therapeutic agents are no longer viable. Because N. gonorrhoeae infections are not reportable in Germany, only limited data on disease epidemiology and antimicrobial susceptibility patterns are available. The Gonococcal Resistance Network (GORENET) is a surveillance project to monitor trends in the antimicrobial susceptibility of N. gonorrhoeae in Germany in order to guide treatment algorithms and target future prevention strategies.

Methods

Between April 2014 and December 2015, data on patient-related information were collected from laboratories nationwide, and susceptibility testing was performed on 537 N. gonorrhoeae isolates forwarded from the network laboratories to the Conciliar Laboratory for gonococci. Susceptibility results for cefixime, ceftriaxone, azithromycin, ciprofloxacin and penicillin were defined according to EUCAST 4.0 standards. Percentages, medians and interquartile ranges (IQR) were calculated.

Results

Altogether, 90% of isolates were from men. The median age was 32 (IQR 25–44) years for men and 25 (IQR 22–40) years for women (p-value < 0.001). The most frequently tested materials among men were urethral (96.1%) and rectal swabs (1.7%), and among women, it was mainly endocervical and vaginal swabs (84.3%). None of the isolates were resistant to ceftriaxone. Furthermore, 1.9% (in 2014) and 1.4% (in 2015) of the isolates were resistant to cefixime, 11.9% and 9.8% showed resistance against azithromycin, 72.0% and 58.3% were resistant to ciprofloxacin, and 29.1% and 18.8% were resistant to penicillin.

Conclusions

Resistance to ceftriaxone was not detected, and the percentage of isolates with resistance to cefixime was low, whereas azithromycin resistance showed high levels during the observation period. The rates of ciprofloxacin resistance and penicillin resistance were very high across Germany. Continued surveillance of antimicrobial drug susceptibilities for N. gonorrhoeae remains highly important to ensure efficient disease management.

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.

ARIBA: rapid antimicrobial resistance genotyping directly from sequencing reads

Antimicrobial resistance (AMR) is one of the major threats to human and animal health worldwide, yet few high-throughput tools exist to analyse and predict the resistance of a bacterial isolate from sequencing data. Here we present a new tool, ARIBA, that identifies AMR-associated genes and single nucleotide polymorphisms directly from short reads, and generates detailed and customizable output. The accuracy and advantages of ARIBA over other tools are demonstrated on three datasets from Gram-positive and Gram-negative bacteria, with ARIBA outperforming existing methods.

Recent advances in the development and use of molecular tests to predict antimicrobial resistance in Neisseria gonorrhoeae

INTRODUCTION

The number of genetic tests, mostly real-time PCRs, to detect antimicrobial resistance (AMR) determinants and predict AMR in Neisseria gonorrhoeae is increasing. Several of these assays are promising, but there are important shortcomings and few assays have been adequately validated and quality assured. Areas covered: Recent advances, focusing on publications since 2012, in the development and use of molecular tests to predict gonococcal AMR for surveillance and for clinical use, advantages and disadvantages of these tests and of molecular AMR prediction compared with phenotypic AMR testing, and future perspectives for effective use of molecular AMR tests for different purposes. Expert commentary: Several challenges for direct testing of clinical, especially extra-genital, specimens remain. The choice of molecular assay needs to consider the assay target, quality controls, sample types, limitations intrinsic to molecular technologies, and specific to the chosen methodology, and the intended use of the test. Improved molecular- and particularly genome-sequencing-based methods will supplement AMR testing for surveillance purposes, and translate into point-of-care tests that will lead to personalized treatments, while sparing the last available empiric treatment option (ceftriaxone). However, genetic AMR prediction will never completely replace phenotypic AMR testing, which detects also AMR due to unknown AMR determinants.

WGS to predict antibiotic MICs for Neisseria gonorrhoeae

Background

Tracking the spread of antimicrobial-resistant Neisseria gonorrhoeae is a major priority for national surveillance programmes.

Objectives

We investigate whether WGS and simultaneous analysis of multiple resistance determinants can be used to predict antimicrobial susceptibilities to the level of MICs in N. gonorrhoeae.

Methods

WGS was used to identify previously reported potential resistance determinants in 681 N. gonorrhoeae isolates, from England, the USA and Canada, with phenotypes for cefixime, penicillin, azithromycin, ciprofloxacin and tetracycline determined as part of national surveillance programmes. Multivariate linear regression models were used to identify genetic predictors of MIC. Model performance was assessed using leave-one-out cross-validation.

Results

Overall 1785/3380 (53%) MIC values were predicted to the nearest doubling dilution and 3147 (93%) within ±1 doubling dilution and 3314 (98%) within ±2 doubling dilutions. MIC prediction performance was similar across the five antimicrobials tested. Prediction models included the majority of previously reported resistance determinants. Applying EUCAST breakpoints to MIC predictions, the overall very major error (VME; phenotypically resistant, WGS-prediction susceptible) rate was 21/1577 (1.3%, 95% CI 0.8%-2.0%) and the major error (ME; phenotypically susceptible, WGS-prediction resistant) rate was 20/1186 (1.7%, 1.0%-2.6%). VME rates met regulatory thresholds for all antimicrobials except cefixime and ME rates for all antimicrobials except tetracycline. Country of testing was a strongly significant predictor of MIC for all five antimicrobials.

Conclusions

We demonstrate a WGS-based MIC prediction approach that allows reliable MIC prediction for five gonorrhoea antimicrobials. Our approach should allow reasonably precise prediction of MICs for a range of bacterial species.

A Case-Control Study of Molecular Epidemiology in Relation to Azithromycin Resistance in Neisseria gonorrhoeae Isolates Collected in Amsterdam, the Netherlands, between 2008 and 2015

Neisseria gonorrhoeae resistance to ceftriaxone and azithromycin is increasing, which threatens the recommended dual therapy. We used molecular epidemiology to identify N. gonorrhoeae clusters and associations with azithromycin resistance in Amsterdam, the Netherlands. N. gonorrhoeae isolates (n = 143) were selected from patients visiting the Amsterdam STI Outpatient Clinic from January 2008 through September 2015. We included all 69 azithromycin-resistant isolates (MIC ≥ 2.0 mg/liter) and 74 frequency-matched susceptible controls (MIC ≤ 0.25 mg/liter). The methods used were 23S rRNA and mtrR sequencing, N. gonorrhoeae multiantigen sequence typing (NG-MAST), N. gonorrhoeae multilocus variable-number tandem-repeat analysis (NG-MLVA), and a specific PCR to detect mosaic penA genes. A hierarchical cluster analysis of NG-MLVA related to resistance and epidemiological characteristics was performed. Azithromycin-resistant isolates had C2611T mutations in 23S rRNA (n = 62, 89.9%, P < 0.001) and were NG-MAST genogroup G2992 (P < 0.001), G5108 (P < 0.001), or G359 (P = 0.02) significantly more often than susceptible isolates and were more often part of NG-MLVA clusters (P < 0.001). Two resistant isolates (2.9%) had A2059G mutations, and five (7.3%) had wild-type 23S rRNA. No association between mtrR mutations and azithromycin resistance was found. Twenty-four isolates, including 10 azithromycin-resistant isolates, showed reduced susceptibility to extended-spectrum cephalosporins. Of these, five contained a penA mosaic gene. Four of the five NG-MLVA clusters contained resistant and susceptible isolates. Two clusters consisting mainly of resistant isolates included strains from men who have sex with men and from heterosexual males and females. The co-occurrence of resistant and susceptible strains in NG-MLVA clusters and the frequent occurrence of resistant strains outside of clusters suggest that azithromycin resistance develops independently from the background genome.

Azithromycin Resistance and Decreased Ceftriaxone Susceptibility in Neisseria gonorrhoeae, Hawaii, USA

During 2016, eight Neisseria gonorrhoeae isolates from 7 patients in Hawaii were resistant to azithromycin; 5 had decreased in vitro susceptibility to ceftriaxone. Genomic analysis demonstrated a distinct phylogenetic clade when compared with local contemporary strains. Continued evolution and widespread transmission of these strains might challenge the effectiveness of current therapeutic options.

Ribosomal Mutations Conferring Macrolide Resistance in Legionella pneumophila

Monitoring the emergence of antibiotic resistance is a recent issue in the treatment of Legionnaires' disease. Macrolides are recommended as first-line therapy, but resistance mechanisms have not been studied in Legionella species. Our aim was to determine the molecular basis of macrolide resistance in L. pneumophila Twelve independent lineages from a common susceptible L. pneumophila ancestral strain were propagated under conditions of erythromycin or azithromycin pressure to produce high-level macrolide resistance. Whole-genome sequencing was performed on 12 selected clones, and we investigated mutations common to all lineages. We reconstructed the dynamics of mutation for each lineage and demonstrated their involvement in decreased susceptibility to macrolides. The resistant mutants were produced in a limited number of passages to obtain a 4,096-fold increase in erythromycin MICs. Mutations affected highly conserved 5-amino-acid regions of L4 and L22 ribosomal proteins and of domain V of 23S rRNA (G2057, A2058, A2059, and C2611 nucleotides). The early mechanisms mainly affected L4 and L22 proteins and induced a 32-fold increase in the MICs of the selector drug. Additional mutations related to 23S rRNA mostly occurred later and were responsible for a major increase of macrolide MICs, depending on the mutated nucleotide, the substitution, and the number of mutated genes among the three rrl copies. The major mechanisms of the decreased susceptibility to macrolides in L. pneumophila and their dynamics were determined. The results showed that macrolide resistance could be easily selected in L. pneumophila and warrant further investigations in both clinical and environmental settings.

Neisseria gonorrhoeae Sequence Typing for Antimicrobial Resistance, a Novel Antimicrobial Resistance Multilocus Typing Scheme for Tracking Global Dissemination of N. gonorrhoeae Strains

A curated Web-based user-friendly sequence typing tool based on antimicrobial resistance determinants in Neisseria gonorrhoeae was developed and is publicly accessible (https://ngstar.canada.ca). The N. gonorrhoeae Sequence Typing for Antimicrobial Resistance (NG-STAR) molecular typing scheme uses the DNA sequences of 7 genes (penA, mtrR, porB, ponA, gyrA, parC, and 23S rRNA) associated with resistance to β-lactam antimicrobials, macrolides, or fluoroquinolones. NG-STAR uses the entire penA sequence, combining the historical nomenclature for penA types I to XXXVIII with novel nucleotide sequence designations; the full mtrR sequence and a portion of its promoter region; portions of ponA, porB, gyrA, and parC; and 23S rRNA sequences. NG-STAR grouped 768 isolates into 139 sequence types (STs) (n = 660) consisting of 29 clonal complexes (CCs) having a maximum of a single-locus variation, and 76 NG-STAR STs (n = 109) were identified as unrelated singletons. NG-STAR had a high Simpson's diversity index value of 96.5% (95% confidence interval [CI] = 0.959 to 0.969). The most common STs were NG-STAR ST-90 (n = 100; 13.0%), ST-42 and ST-91 (n = 45; 5.9%), ST-64 (n = 44; 5.72%), and ST-139 (n = 42; 5.5%). Decreased susceptibility to azithromycin was associated with NG-STAR ST-58, ST-61, ST-64, ST-79, ST-91, and ST-139 (n = 156; 92.3%); decreased susceptibility to cephalosporins was associated with NG-STAR ST-90, ST-91, and ST-97 (n = 162; 94.2%); and ciprofloxacin resistance was associated with NG-STAR ST-26, ST-90, ST-91, ST-97, ST-150, and ST-158 (n = 196; 98.0%). All isolates of NG-STAR ST-42, ST-43, ST-63, ST-81, and ST-160 (n = 106) were susceptible to all four antimicrobials. The standardization of nomenclature associated with antimicrobial resistance determinants through an internationally available database will facilitate the monitoring of the global dissemination of antimicrobial-resistant N. gonorrhoeae strains.

Use of whole-genome sequencing data to analyze 23S rRNA-mediated azithromycin resistance

The whole-genome sequences of 24 isolates of Neisseria gonorrhoeae with elevated minimum inhibitory concentrations (MICs) to azithromycin (≥2.0 µg/mL) were analyzed against a modified sequence derived from the whole-genome sequence of N. gonorrhoeae FA1090 to determine, by signal ratio, the number of mutant copies of the 23S rRNA gene and the copy number effect on 50S ribosome-mediated azithromycin resistance. Isolates that were predicted to contain four mutated copies were accurately identified compared with the results of direct sequencing. Fewer than four mutated copies gave less accurate results but were consistent with elevated MICs.

The role of whole genome sequencing in antimicrobial susceptibility testing of bacteria: report from the EUCAST Subcommittee

Whole genome sequencing (WGS) offers the potential to predict antimicrobial susceptibility from a single assay. The European Committee on Antimicrobial Susceptibility Testing established a subcommittee to review the current development status of WGS for bacterial antimicrobial susceptibility testing (AST). The published evidence for using WGS as a tool to infer antimicrobial susceptibility accurately is currently either poor or non-existent and the evidence / knowledge base requires significant expansion. The primary comparators for assessing genotypic-phenotypic concordance from WGS data should be changed to epidemiological cut-off values in order to improve differentiation of wild-type from non-wild-type isolates (harbouring an acquired resistance). Clinical breakpoints should be a secondary comparator. This assessment will reveal whether genetic predictions could also be used to guide clinical decision making. Internationally agreed principles and quality control (QC) metrics will facilitate early harmonization of analytical approaches and interpretive criteria for WGS-based predictive AST. Only data sets that pass agreed QC metrics should be used in AST predictions. Minimum performance standards should exist and comparative accuracies across different WGS laboratories and processes should be measured. To facilitate comparisons, a single public database of all known resistance loci should be established, regularly updated and strictly curated using minimum standards for the inclusion of resistance loci. For most bacterial species the major limitations to widespread adoption for WGS-based AST in clinical laboratories remain the current high-cost and limited speed of inferring antimicrobial susceptibility from WGS data as well as the dependency on previous culture because analysis directly on specimens remains challenging. For most bacterial species there is currently insufficient evidence to support the use of WGS-inferred AST to guide clinical decision making. WGS-AST should be a funding priority if it is to become a rival to phenotypic AST. This report will be updated as the available evidence increases.

New treatment options for infections caused by increasingly antimicrobial-resistant Neisseria gonorrhoeae

The emergence of high-level resistance to ceftriaxone is giving rise to serious concern about absence of effective treatment options to cure gonococcal infections. Increasing the dosage regimen can be applied to ceftriaxone and azithromycin, but the emergence of high-level resistance has already been reported. Spectinomycin is another active drug but has low efficacy in the treatment of pharyngeal gonorrhoea. Conventional antibiotics could be introduced for gonococcal treatment, but they have some limitations, such as the absence of clinical trials and breakpoint. Combining antibiotics is another promising method to cure patients and to prevent the emergence of resistance. The most important strategy to maintain the efficacy of antibiotics is rapid detection and dissemination control of novel resistant isolate.

Molecular tests for the detection of antimicrobial resistant Neisseria gonorrhoeae: when, where, and how to use?

PURPOSE OF REVIEW

Molecular methods for the diagnosis of Neisseria gonorrhoeae are replacing bacterial culture in many settings. This review focuses on recent progress in the development of molecular tests to detect resistant N. gonorrhoeae both to enhance surveillance and to guide decisions about individual patient management.

RECENT FINDINGS

Assays to enhance surveillance have been developed to detect determinants of resistance for all antibiotics used as first-line gonorrhoea treatment, or to detect specific 'superbug' strains, but few have been applied in clinical practice. The most advanced strategy relevant to individual case management is to identify ciprofloxacin-sensitive strains so that unnecessary use of ceftriaxone can be avoided. Cross-reactivity with pharyngeal commensal Neisseria species reduces specificity and is a challenge for many assays.

SUMMARY

Progress with laboratory-based molecular tests to detect gonococcal resistance is being made but substantial challenges remain. No laboratory-based assay has been subjected to a field evaluation and no assay so far can be used as a point-of-care test. Given the threat of antimicrobial resistance, now is the time to exploit the molecular technologies used for diagnosis and to invest in the development of molecular gonococcal resistance tests that can be implemented for public health good.

The Molecular Epidemiology and Antimicrobial Resistance of Neisseria gonorrhoeae in Australia: A Nationwide Cross-Sectional Study, 2012

BACKGROUND

 Antimicrobial resistance (AMR) by Neisseria gonorrhoeae is considered a serious global threat.

METHODS

 In this nationwide study, we used MassARRAY iPLEX genotyping technology to examine the epidemiology of N. gonorrhoeae and associated AMR in the Australian population. All available N. gonorrhoeae isolates (n = 2452) received from Australian reference laboratories from January to June 2012 were included in the study. Genotypic data were combined with phenotypic AMR information to define strain types.

RESULTS

 A total of 270 distinct strain types were observed. The 40 most common strain types accounted for over 80% of isolates, and the 10 most common strain types accounted for almost half of all isolates. The high male to female ratios (>94% male) suggested that at least 22 of the top 40 strain types were primarily circulating within networks of men who have sex with men (MSM). Particular strain types were also concentrated among females: two strain types accounted for 37.5% of all isolates from females. Isolates harbouring the mosaic penicillin binding protein 2 (PBP2)-considered a key mechanism for cephalosporin resistance-comprised 8.9% of all N. gonorrhoeae isolates and were primarily observed in males (95%).

CONCLUSIONS

 This large scale epidemiological investigation demonstrated that N. gonorrhoeae infections are dominated by relatively few strain types. The commonest strain types were concentrated in MSM in urban areas and Indigenous heterosexuals in remote areas, and we were able to confirm a resurgent epidemic in heterosexual networks in urban areas. The prevalence of mosaic PBP2 harboring N. gonorrhoeae strains highlight the ability for new N. gonorrhoeae strains to spread and become established across populations.