Molecular analysis of antimicrobial resistance mechanisms in Neisseria gonorrhoeae isolates from Ontario, Canada

Antimicrobial resistance in Neisseria gonorrhoeae in the 21st century: past, evolution, and future

Neisseria gonorrhoeae is evolving into a superbug with resistance to previously and currently recommended antimicrobials for treatment of gonorrhea, which is a major public health concern globally. Given the global nature of gonorrhea, the high rate of usage of antimicrobials, suboptimal control and monitoring of antimicrobial resistance (AMR) and treatment failures, slow update of treatment guidelines in most geographical settings, and the extraordinary capacity of the gonococci to develop and retain AMR, it is likely that the global problem of gonococcal AMR will worsen in the foreseeable future and that the severe complications of gonorrhea will emerge as a silent epidemic. By understanding the evolution, emergence, and spread of AMR in N. gonorrhoeae, including its molecular and phenotypic mechanisms, resistance to antimicrobials used clinically can be anticipated, future methods for genetic testing for AMR might permit region-specific and tailor-made antimicrobial therapy, and the design of novel antimicrobials to circumvent the resistance problems can be undertaken more rationally. This review focuses on the history and evolution of gonorrhea treatment regimens and emerging resistance to them, on genetic and phenotypic determinants of gonococcal resistance to previously and currently recommended antimicrobials, including biological costs or benefits; and on crucial actions and future advances necessary to detect and treat resistant gonococcal strains and, ultimately, retain gonorrhea as a treatable infection.

Antibiotic resistance in prevalent bacterial and protozoan sexually transmitted infections

The emergence of multi-drug resistant sexually transmitted infections (STIs) is causing a treatment crisis across the globe. While cephalosporin-resistant gonorrhea is one of the most pressing issues, extensively antibiotic resistant Chlamydia trachomatis and Mycoplasma hominis are also becoming commonplace. Experts have suggested that the failure of current treatment regimens are "largely inevitable" and have called for entirely new classes of antimicrobial agents. With the exception of several new classes of drugs primarily targeting nosocomial infections, progress has been slow. While pharmaceutical companies continue to introduce new drugs, they are based on decade-old discoveries. While there is disagreement about what constitutes new classes of antibiotics, many experts suggest that the last truly new family of antimicrobials was discovered in 1987. This review summarizes the existing literature on antibiotic resistance in common bacterial and protozoal STIs. It also briefly discusses several of the most promising alternatives to current therapies, and further examines how advances in drug delivery, formulation, concentration, and timing are improving the efficacy of existing treatments. Finally, the paper discusses the current state of pharmaceutical development for multidrug-resistant STI.

Antibiotic resistance in prevalent bacterial and protozoan sexually transmitted infections

The emergence of multi-drug resistant sexually transmitted infections (STIs) is causing a treatment crisis across the globe. While cephalosporin-resistant gonorrhea is one of the most pressing issues, extensively antibiotic resistant Chlamydia trachomatis and Mycoplasma hominis are also becoming commonplace. Experts have suggested that the failure of current treatment regimens are "largely inevitable" and have called for entirely new classes of antimicrobial agents. With the exception of several new classes of drugs primarily targeting nosocomial infections, progress has been slow. While pharmaceutical companies continue to introduce new drugs, they are based on decade-old discoveries. While there is disagreement about what constitutes new classes of antibiotics, many experts suggest that the last truly new family of antimicrobials was discovered in 1987. This review summarizes the existing literature on antibiotic resistance in common bacterial and protozoal STIs. It also briefly discusses several of the most promising alternatives to current therapies, and further examines how advances in drug delivery, formulation, concentration, and timing are improving the efficacy of existing treatments. Finally, the paper discusses the current state of pharmaceutical development for multidrug-resistant STI.

Antimicrobial susceptibility of Neisseria gonorrhoeae isolates from symptomatic men attending the Nanjing sexually transmitted diseases clinic (2011-2012): genetic characteristics of isolates with reduced sensitivity to ceftriaxone

BACKGROUND

Evolving gonococcal antimicrobial resistance (AMR) poses a serious threat to public health. The aim of this study was to: update antimicrobial susceptibility data of Neisseria gonorrhoeae recently isolated in Nanjing, China and identify specific deteminants of antimicrobial resistance and gentoypes of isolates with decreased sensitivity to ceftriaxone.

METHODS

334 N. gonorrhoeae isolates were collected consecutively from symptomatic men attending the Nanjing STD Clinic between April 2011 and December 2012. The minimum inhibitory concentrations (MICs) for penicillin, tetracycline, ciprofloxacin, spectinomycin and ceftriaxone were determined by agar plate dilution for each isolate. Penicillinase-producing N. gonorrhoeae (PPNG) and tetracycline-resistant N. gonorrhoeae (TRNG) were examined and typed for β-lactamase and tetM encoding plasmids respectively. Isolates that displayed elevated MICs to ceftriaxone (MIC ≥0.125 mg/L) were also tested for mutations in penA, mtrR, porB1b, ponA and pilQ genes and characterized by Neisseria gonorrhoeae multi-antigen sequence typing (NG-MAST).

RESULTS

98.8% (330/334) of N. gonorrhoeae isolates were resistant to ciprofloxacin; 97.9% (327/334) to tetracycline and 67.7% (226/334) to penicillin. All isolates were susceptible to ceftriaxone (MIC ≤0.25 mg/L) and spectinomycin (MIC ≤32 mg/L). Plasmid mediated resistance was exhibited by 175/334 (52%) of isolates: 120/334 (36%) of isolates were PPNG and 104/334 (31%) were TRNG. 90.0% (108/120) of PPNG isolates carried the Asia type β-lactamase encoding plasmid and 96% (100/104) of TRNG isolates carried the Dutch type tetM containing plasmid. Elevated MICs for ceftriaxone were present in 15 (4.5%) isolates; multiple mutations were found in penA, mtrR, porB1b and ponA genes. The 15 isolates were distributed into diverse NG-MAST sequence types; four different non-mosaic penA alleles were identified, including one new type.

CONCLUSIONS

N. gonorrhoeae isolates in Nanjing generally retained similar antimicrobial resistance patterns to isolates obtained five years ago. Fluctuations in resistance plasmid profiles imply that genetic exchange among gonococcal strains is ongoing and is frequent. Ceftriaxone and spectinomycin remain treatments of choice of gonorrhea in Nanjing, however, decreased susceptibility to ceftriaxone and rising MICs for spectinomycin of N. gonorrhoeae isolates underscore the importance of maintaining surveillance for AMR (both phenotypic and genotypic).

High-level azithromycin-resistant Neisseria gonorrhoeae clinical isolate in France, March 2014

We report the first case in France of a high-level azithromycin-resistant Neisseria gonorrhoeae (minimum inhibitory concentration (MIC) = 96 mg/L) assigned to MLST7363 (NG-MAST ST6360), also resistant to ciprofloxacin and tetracycline but susceptible to ceftriaxone. The patient was a 51 year-old heterosexual man who returned following 1g azithromycin monotherapy. Mechanisms of azithromycin resistance were a C2599T mutation in the four copies of the rrl gene and a novel mutation in the promoter of the mtrR gene.

Azithromycin resistance is coevolving with reduced susceptibility to cephalosporins in Neisseria gonorrhoeae in Ontario, Canada

Azithromycin (AZM) is routinely recommended as a component of dual therapy for gonorrhea in combination with third-generation cephalosporins (3GC). In this study, we examined the prevalence of AZM-resistant (AZM(r)) Neisseria gonorrhoeae from July 2010 to February 2013, assessed the rate of concurrent cephalosporin resistance under the current treatment recommendations, and analyzed the clonal distribution of AZM(r) isolates in Ontario, Canada. Nineteen AZM(r) clinical isolates (one per patient; MIC, ≥2 μg/ml) were included in the study. Susceptibility profiles of these isolates to 11 antibiotics, molecular typing, characterization of macrolide resistance mechanisms, and penicillin-binding protein 2 (PBP2) patterns were determined for all the isolates. Two groups were defined based on AZM(r) level; group A isolates displayed high-level resistance (MIC, ≥2,048 μg/ml) due to mutations (A2143G) in the four copies of the 23S rRNA rrl gene, and group B isolates had moderate resistance to AZM (MICs, 2 to 8 μg/ml, C2599T mutation in the rrl gene), with a subgroup belonging to sequence type 3158 (ST3158) (n = 8), which also showed reduced susceptibility to 3GC (MICs, 0.12 to 0.25 μg/ml, PBP2 pattern XXXIV). This AZM(r) phenotype was not observed in previous provincial surveillance in 2008 (the ST3158 clone was found, with AZM MICs of 0.25 to 0.5 μg/ml associated with mtrR mutations). We hypothesized that the AZM mutant prevention concentration (MPC) in the ST3158 subpopulation we found in 2008 was higher than the MPC in wild-type isolates (AZM MIC, ≤0.031 μg/ml), increasing the chances of additional selection of AZM(r) mutations. Full AZM resistance is now emerging in this clone together with reduced susceptibility to 3GC, threatening the future efficacy of these antibiotics as therapeutic options for treatment of gonorrhea.

Characterization of Neisseria gonorrhoeae isolates detected in Switzerland (1998-2012): emergence of multidrug-resistant clones less susceptible to cephalosporins

BACKGROUND

The spread of Neisseria gonorrhoeae (Ng) isolates resistant to the clinically implemented antibiotics is challenging the efficacy of treatments. Unfortunately, phenotypic and molecular data regarding Ng detected in Switzerland are scarce.

METHODS

We compared the characteristics of Ng detected during 1998-2001 (n = 26) to those detected during 2009-2012 (n = 34). MICs were obtained with the Etest and interpreted as non-susceptible (non-S) according to EUCAST criteria. Sequence type (ST) was achieved implementing the NG-MAST. BlaTEM, ponA, penA, mtrR, penB, tet(M), gyrA, parC, mefA, ermA/B/C/F, rplD, rplV, and 23S rRNA genes were analyzed.

RESULTS

The following susceptibility results were obtained (period: % of non-S, MIC90 in mg/L): penicillin (1998-2001: 42.3%, 3; 2009-2012: 85.3%, 16), cefixime (1998-2001: 0%, ≤0.016; 2009-2012: 8.8%, 0.125), ceftriaxone (1998-2001: 0%, 0.004; 2009-2012: 0%, 0.047), ciprofloxacin (1998-2001: 7.7%, 0.006; 2009-2012: 73.5%, ≥32), azithromycin (1998-2001: 11.5%, 0.25; 2009-2012: 23.6%, 0.38), tetracycline (1998-2001: 65.4%, 12; 2009-2012: 88.2%, 24), spectinomycin (1998-2001: 0%, 12; 2009-2012: 0%, 8). The prevalence of multidrug-resistant (MDR) isolates increased from 7.7% in 1998-2001 to 70.6% in 2009-2012. International STs and genogroups (G) emerged during 2009-2012 (G1407, 29.4%; G2992, 11.7%; G225, 8.8%). These isolates possessed distinctive mechanisms of resistance (e.g., G1407: PBP1 with L421, PBP2 pattern XXXIV, GyrA with S91F and D95G, ParC with S87R, PorB with G120K and A121N, mtrR promoter with A deletion).

CONCLUSIONS

The prevalence of penicillin- ciprofloxacin- and tetracycline-resistant Ng has reached dramatic levels, whereas cefixime and ceftriaxone show MICs that tend to increase during time. International MDR clones less susceptible to cephalosporins are rapidly emerging indicating that the era of untreatable gonococcal infections is close.

Behavioral and socioeconomic risk factors associated with probable resistance to ceftriaxone and resistance to penicillin and tetracycline in Neisseria gonorrhoeae in Shanghai

Globally, incidence of Neisseria gonorrhoeae infection is once again the highest of the bacterial sexually transmitted infections. The bacterium can produce serious complications in those infected, and emerging resistance to third generation cephalosporins could usher in an era of potentially untreatable gonorrhea. This research aimed to identify risk factors for antibiotic resistant gonorrhea infection among clients at a Shanghai sexually transmitted infection clinic over two time periods, 2004-2005 and 2008-2011. Demographic and risk factor behavior data, and biological samples for antimicrobial resistance analysis, were collected. Statistical models were built to identify risk factors associated with probable resistance to ceftriaxone and resistance to penicillin and tetracycline. High levels of ciprofloxacin resistance (98%) in our sample precluded examining its risk factors; all isolates were susceptible to spectinomycin. Overall (P<0.001), chromosomal (P<0.001), and plasmid-mediated (P = 0.01) penicillin resistance decreased from the first to second period of the study. For tetracycline, chromosomal resistance decreased (P = 0.01) and plasmid-mediated resistance increased (P<0.001) between the first and second periods of study. In multi-level multivariable regression models, male gender (P = 0.03) and older age (P = 0.01) were associated with increased minimum inhibitory concentrations to ceftriaxone. Male gender (P = 0.03) and alcohol use (P = 0.02) were associated with increased odds of overall tetracycline resistance. Male gender was associated with increased odds of chromosomally-mediated tetracycline resistance (P = 0.04), and alcohol use was associated with increased odds of plasmid-mediated tetracycline resistance (P = 0.02). Additionally, individuals in middle-salary categories were found to have lower odds of plasmid-mediated resistance to tetracycline compared with those in the lowest salary category (P≤0.02). This study is one of the first to use multilevel analysis to consider the association between risk factors for gonorrhea infections and mechanisms of resistance to individual antibiotics. Such information is urgently needed to combat the growing threat of untreatable gonorrhea.

Unique combined penA/mtrR/porB mutations and NG-MAST strain types associated with ceftriaxone and cefixime MIC increases in a 'susceptible' Neisseria gonorrhoeae population

OBJECTIVES

To determine which mutations in penA, mtrR and porB are implicated in increasing minimum MICs of ceftriaxone and cefixime in a susceptible gonococcal population and to ascertain associations with gonococcal strain types (STs).

METHODS

One hundred and forty-six Neisseria gonorrhoeae isolates formed two extended-spectrum cephalosporin susceptibility groups: group 1 isolates with cefixime and ceftriaxone MICs of 0.0005-0.016 mg/L; and group 2 isolates with cefixime MICs of 0.03-0.125 mg/L (n = 24) and ceftriaxone MICs of 0.03-0.06 mg/L (n = 23). Mutation patterns in penicillin-binding protein 2 (PBP2; penA), multiple transfer resistance repressor (MtrR; mtrR) and porin B (PorB; porB) were ascertained by DNA sequence and bioinformatic analysis. STs were determined using N. gonorrhoeae multiantigen sequence typing (NG-MAST).

RESULTS

Most isolates carried PBP2 mutation pattern IX (D345a, F504L, A510V, A516G and P551L; 50/146, 34.2%), a G45D substitution in MtrR (37.7%) and a wild-type (WT) sequence for PorB (43.2%). Group 2 gonococcal isolates were significantly associated with: penA pattern IX; dual mutations in the promoter (A-) and DNA dimerization domain (H105Y) of MtrR; and G120K;A121D substitutions in PorB. There were 50 combined penA/mtrR/porB mutation patterns, with corresponding patterns I/WT/WT and IX/G45D/G120K;A121D predominating. Gonococci susceptible to ceftriaxone and cefixime were significantly associated with NG-MAST ST 25 (33/36; 92%) and the combined penA/mtrR/porB mutation pattern I/WT/WT. No combined mutation pattern or specific ST was associated with elevated ceftriaxone MICs. NG-MAST ST 3654 was significantly associated with the pattern IX/G45D/G120K;A121D and cefixime group 2 isolates.

CONCLUSIONS

Specific single or combined mutation patterns in penA, mtrR and porB and specific STs were associated with differences in susceptibility to ceftriaxone and cefixime.

Molecular epidemiology of Neisseria gonorrhoeae isolates from Saskatchewan, Canada: utility of NG-MAST in predicting antimicrobial susceptibility regionally

OBJECTIVES

To investigate the molecular epidemiology of isolates of Neisseria gonorrhoeae from Saskatchewan, Canada, using Neisseria gonorrhoeae multi antigen sequence typing (NG-MAST), and to assess associations between antimicrobial susceptibility (AMS) and specific strain types (STs).

METHODS

320 consecutive gonococcal isolates, collected between 2003 and 2008, were typed by NG-MAST. STs were grouped if one of their alleles was common and the other differed by ≤1% in DNA sequence. AMS was determined by agar dilution (CLSI) to seven antibiotics.

RESULTS

N gonorrhoeae isolates were resolved into 82 individual NG-MAST STs and 18 NG-MAST ST groups with groups 25, 3655, 921, 3654, 3657 and 3656 comprising 53.4% (171/320) of the isolates. N gonorrhoeae isolates susceptible to all the tested antimicrobials were significantly (p<0.05) associated with ST 25 (87%). Other significant associations between ST and AMS included: ST 3654 and isolates with minimum inhibitory concentrations of ≥0.03 mg/L to third generation cephalosporins; ST 3711 (100%) and TRNG; and ST/group 3654 (43%) and chromosomal resistance to penicillin and tetracycline. Several NG-MAST STs/groups were significantly associated with isolates with chromosomal resistance to tetracycline. Isolates resistant to ciprofloxacin (n=5) and azithromycin (n=2) appeared as individual STs. Significant associations were observed among individual STs, sex and age of the patient, and regional and temporal distributions.

CONCLUSIONS

Associations between N gonorrhoeae AMS and NG-MAST STs were identified and may be useful in predicting AMS regionally. Because STs in different countries vary considerably, the use of NG-MAST for the prediction of AMS globally requires further study.

Molecular diagnostics for gonorrhoea: implications for antimicrobial resistance and the threat of untreatable gonorrhoea

This Essay from Nicola Low and colleagues discusses the importance of the nucleic acid amplification tests for rapid detection of N. gonorrhoeae and its resistance determinants, as well as the importance of ensuring their rational use, as priorities for controlling both gonorrhoea and antimicrobial resistance.

Please see later in the article for the Editors' Summary

Worldwide susceptibility rates of Neisseria gonorrhoeae isolates to cefixime and cefpodoxime: a systematic review and meta-analysis

BACKGROUND

Neisseria gonorrhoeae (NG) infection is a serious public health problem. The third-generation extended-spectrum cephalosporins (ESCs) have been used as the first-line treatment for NG infection for almost three decades. However, in recent years, treatment failures with the oral third-generation ESCs have been reported worldwide. This study aimed to estimate worldwide susceptibility rates of NG to cefixime and cefpodoxime by analyzing data from all relevant published studies.

METHODOLOGY/PRINCIPAL FINDINGS

Two researchers independently searched five databases to identify studies on susceptibilities of NG to cefixime and cefpodoxime published between January 1, 1984 and October 15, 2012. A fixed-effect model was used to perform group analysis, and a χ2 test was employed to make subgroup comparison. Publication bias was assessed with the Begg rank correlation test. The pooled susceptibility rate of NG isolates to cefixime was 99.8% (95% CI: 99.7%-99.8%). The cefixime susceptibility rate of NG isolates from men was significantly lower than that from patients without information of gender or from men and women; the susceptibility rate of NG isolates from Asia was significantly lower than that from other continents; and the susceptibility rate of NG isolates collected before or during 2003 was significantly higher than that after 2003. The pooled susceptibility rate of NG isolates to cefpodoxime was 92.8% (95% CI: 89.0%-95.3%), which was lower than that to cefixime (92.8% vs. 99.8%, χ2 = 951.809, P<0.01).

CONCLUSIONS

The susceptibility rate of NG isolates to cefixime varied with the gender of patients and geographical location from which NG isolates were collected, and declined with time. The reported lower susceptibility rate of NG isolates to cefixime and associated treatment failures, as well as the emergence of NG strains with cephalosporin resistance call for the more effective control of NG infection and the development of new antibiotics.

Neisseria gonorrhoeae and extended-spectrum cephalosporins in California: surveillance and molecular detection of mosaic penA

BACKGROUND

The spread of Neisseria gonorrhoeae strains with mosaic penA alleles and reduced susceptibility to extended-spectrum cephalosporins is a major public health problem. While much work has been performed internationally, little is known about the genetics or molecular epidemiology of N. gonorrhoeae isolates with reduced susceptibility to extended-spectrum cephalosporins in the United States. The majority of N. gonorrhoeae infections are diagnosed without a live culture. Molecular tools capable of detecting markers of extended-spectrum cephalosporin resistance are needed.

METHODS

Urethral N. gonorrhoeae isolates were collected from 684 men at public health clinics in California in 2011. Minimum inhibitory concentrations (MICs) to ceftriaxone, cefixime, cefpodoxime and azithromycin were determined by Etest and categorized according to the U.S. Centers for Disease Control 2010 alert value breakpoints. 684 isolates were screened for mosaic penA alleles using real-time PCR (RTPCR) and 59 reactive isolates were subjected to DNA sequencing of their penA alleles and Neisseria gonorrhoeae multi-antigen sequence typing (NG-MAST). To increase the specificity of the screening RTPCR in detecting isolates with alert value extended-spectrum cephalosporin MICs, the primers were modified to selectively amplify the mosaic XXXIV penA allele.

RESULTS

Three mosaic penA alleles were detected including two previously described alleles (XXXIV, XXXVIII) and one novel allele (LA-A). Of the 29 isolates with an alert value extended-spectrum cephalosporin MIC, all possessed the mosaic XXXIV penA allele and 18 were sequence type 1407, an internationally successful strain associated with multi-drug resistance. The modified RTPCR detected the mosaic XXXIV penA allele in urethral isolates and urine specimens and displayed no amplification of the other penA alleles detected in this study.

CONCLUSION

N. gonorrhoeae isolates with mosaic penA alleles and reduced susceptibility to extended-spectrum cephalosporins are currently circulating in California. Isolates with the same NG-MAST ST, penA allele and extended-spectrum cephalosporin MICs have caused treatment failures elsewhere. The RTPCR assay presented here may be useful for the detection of N. gonorrheoae isolates and clinical specimens with reduced extended-spectrum cephalosporin MICs in settings where antimicrobial susceptibility testing is unavailable. In an era of increasing antimicrobial resistance and decreasing culture capacity, molecular assays capable of detecting extended-spectrum cephalosporin of resistance are essential to public health.

Antimicrobial activity of solithromycin against clinical isolates of Legionella pneumophila serogroup 1

The activity of solithromycin was evaluated against clinical Legionella pneumophila serogroup 1 (Lp1) isolates (n = 196) collected in Ontario, Canada, from 1980 to 2011. Its in vitro activity was compared to that of azithromycin (AZM) using the broth microdilution method. Solithromycin had a MIC50 of ≤0.015 μg/ml and a MIC90 of 0.031 μg/ml, making its activity at least 8-fold to 32-fold higher than that of AZM (MIC50 and MIC90, 0.125 μg/ml and 1 μg/ml, respectively). Ninety-nine percent of the isolates had MICs for solithromycin ranging from ≤0.015 μg/ml to 0.031 μg/ml, whereas 83.6% of the isolates showed MICs for AZM ranging from 0.062 μg/ml to 0.25 μg/ml. Interestingly, 96.7% (30 out of 31 clinical isolates) identified with higher AZM MICs (0.5 μg/ml to 2 μg/ml) belonged to the clinically prevalent sequence type 1. To investigate the intracellular activity of solithromycin, in vitro invasion assays were also performed against a subset of representative Lp1 isolates internalized within human lung epithelial cells. Solithromycin and AZM both inhibited growth of all intracellular Lp1 isolates at 1× or 8× MICs, displaying bacteriostatic effects, as would be expected with protein synthesis inhibitor rather than bactericidal activity. Solithromycin demonstrated the highest in vitro and intracellular potency against all Lp1 isolates compared to AZM. Given the rapid spread of resistance mechanisms among respiratory pathogens and the reported treatment failures in legionellosis, the development of this new fluoroketolide, already in phase 3 oral clinical studies, constitutes a promising alternative option for the treatment of legionellosis.

Utility of specimens positive for Neisseria gonorrhoeae by the Aptima Combo 2 assay for assessment of strain diversity and antibiotic resistance

In our jurisdiction, the Aptima Combo 2 assay (Gen-Probe, Inc.) is used to detect Neisseria gonorrhoeae from specimens collected at clinics for sexually transmitted infections (STI) and from select community patients. In addition, swabs are also collected for N. gonorrhoeae culture, susceptibility testing, and sequence typing (ST). Since only a small proportion of samples from provincial cases undergo culture, the available trends in antimicrobial susceptibility and predominant strain types may not be representative of all N. gonorrhoeae infections. Due to the limitations facing the use of N. gonorrhoeae culture to understand these trends in the general community, we performed a molecular analysis for markers of cephalosporin resistance and ST determination by using nucleic acid extracts of specimens sent for Aptima testing. Thirty-four samples submitted for both Aptima testing and N. gonorrhoeae culture from the same anatomic location (within 24 h) were included in the study. Sequence type was determined based on the sequence of the por and tbpB genes, and amino acid changes in the PBP 2 protein, encoded by the penA gene, were considered representative for the assessment of antimicrobial susceptibility. Sequence identity of 100% was observed between the sequences obtained from Aptima-analyzed samples and culture samples. Sequencing results showed an association between decreased susceptibility to extended-spectrum cephalosporins (ESC(ds)), tbp allele 110, ST 1407, and amino acid changes (G545S, I312M, and V316T) in the PBP 2 protein. Our data, generated based on a few representative genes, suggest that gonococcal samples positive by Aptima testing can be used to determine single nucleotide polymorphisms associated with ESC(ds) and the sequence type based on molecular strain typing. Confirmation of these findings may obviate the need for gonorrhea culture in the future.

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

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

Determination of In Vitro Activities of Solithromycin at Different pHs and Its Intracellular Activity against Clinical Isolates of Neisseria gonorrhoeae from a Laboratory Collection

We evaluated the activity of solithromycin against 196 clinical gonococcal isolates collected at the Public Health Ontario Laboratories, Toronto, Canada, including isolates with different levels of azithromycin resistance, as well as the role of pH in MIC determinations using pH-adjusted agar plates (pH range, 5.6 to 7.6). In vitro invasion assays were performed using monolayers of HeLa epithelial cells and clinical gonococci displaying different azithromycin MICs; infected cultures were treated with solithromycin, and its intracellular activity was determined by CFU assays after 3 and 20 h of exposure. Solithromycin displayed a MIC₅₀ and MIC₉₀ of 0.0625 and 0.125 μg/ml, respectively, making its activity at least 4-fold higher than that of azithromycin. Clinical isolates with elevated MICs for azithromycin (MICs of ≥2,048 μg/ml and 4 to 8 μg/ml) showed solithromycin MIC values of 8 and 0.5 μg/ml, respectively. In contrast to azithromycin, solithromycin MICs were not significantly affected by acidic pHs, suggesting more stability at lower pH. Moreover, when intracellular Neisseria gonorrhoeae isolates were incubated with solithromycin at 4 times, 1 times, and one-fourth of the MIC, the exposure to solithromycin resulted in the progressive loss of viability of most isolates over time. The intracellular activity of solithromycin, combined with the low MICs to this agent, indicates that it may be an attractive option for gonorrhea treatment if clinical trials in development reveal that this drug can be used safely in adult indications, especially when multidrug-resistant clinical isolates are now emerging.

Revolutionising bacteriology to improve treatment outcomes and antibiotic stewardship

Laboratory investigation of bacterial infections generally takes two days: one to grow the bacteria and another to identify them and to test their susceptibility. Meanwhile the patient is treated empirically, based on likely pathogens and local resistance rates. Many patients are over-treated to prevent under-treatment of a few, compromising antibiotic stewardship. Molecular diagnostics have potential to improve this situation by accelerating precise diagnoses and the early refinement of antibiotic therapy. They include: (i) the use of 'biomarkers' to swiftly distinguish patients with bacterial infection, and (ii) molecular bacteriology to identify pathogens and their resistance genes in clinical specimens, without culture. Biomarker interest centres on procalcitonin, which has given good results particularly for pneumonias, though broader biomarker arrays may prove superior in the future. PCRs already are widely used to diagnose a few infections (e.g. tuberculosis) whilst multiplexes are becoming available for bacteraemia, pneumonia and gastrointestinal infection. These detect likely pathogens, but are not comprehensive, particularly for resistance genes; there is also the challenge of linking pathogens and resistance genes when multiple organisms are present in a sample. Next-generation sequencing offers more comprehensive profiling, but obstacles include sensitivity when the bacterial load is low, as in bacteraemia, and the imperfect correlation of genotype and phenotype. In short, rapid molecular bacteriology presents great potential to improve patient treatments and antibiotic stewardship but faces many technical challenges; moreover it runs counter to the current nostrum of defining resistance in pharmacodynamic terms, rather than by the presence of a mechanism, and the policy of centralising bacteriology services.

Tracing subsequent dissemination of a cluster of gonococcal infections caused by an ST1407-related clone harbouring mosaic penA alleles in Taiwan

OBJECTIVES

Successful clones of Neisseria gonorrhoeae multiantigen sequence typing sequence type (ST) 1407 and ST1407-related genotypes have been reported to cause cefixime and ceftriaxone treatment failure in many countries. We characterized the 47 isolates of a strain cluster of ST4378, a genotype that differs in the porB sequence by only one nucleotide from ST1407, in Taiwan during April 2006 to June 2012.

METHODS

We identified 47 ST4378 isolates among our 2357 total isolates from the Gonococci-National Isolate Collection for Epidemiology. The corresponding patients' medical records were collected. The 47 isolates were further typed by multilocus sequence typing. Genes involved in β-lactam (ponA), quinolone (gyrA and parC) and multidrug (mtrR, porB1b and pilQ) resistance were sequenced. Antimicrobial susceptibility was determined by the disc diffusion test and Etest.

RESULTS

Cefixime MICs for the 47 isolates ranged from 0.016 to 0.19 mg/L and ceftriaxone MICs ranged from 0.012 to 0.094 mg/L. Forty-six of the 47 isolates had a mosaic penA allele type XXXIV and one had a new allele type XL, which appeared to be a recombinant of mosaic penA type XXXIV and non-mosaic penA type II. All of the isolates harboured nearly identical polymorphism in the ponA, gyrA, parC, mtrR, porB1b and pilQ genes. Among the 33 patients with known medical records, 25 (76%) were men who have sex with men (MSM), 3 (9%) were bisexual and 5 (15%) were heterosexual. Fourteen (42%) of the 33 patients had HIV, 8 (24%) had syphilis and 7 (21%) had both infections.

CONCLUSIONS

This is the first report of a cluster of ST1407-related strains in Taiwan. ST4378 is a genotype that may develop to cause third-generation cephalosporin treatment failures. Our results showed that ST4378 strains primarily transmitted in a high-risk MSM/bisexual network. The potential of these strains to become untreatable and spread to other low-risk sexual networks should be closely monitored.

Longitudinal analysis of the evolution and dissemination of Neisseria gonorrhoeae strains (Saskatchewan, Canada, 2005 to 2008) reveals three major circulating strains and convergent evolution of ciprofloxacin and azithromycin resistance

A longitudinal study combining multilocus sequence typing with molecular evolutionary analysis determined the distribution, population structure, and evolution of antibiotic resistance in Neisseria gonorrhoeae isolates in Saskatchewan that were collected between 2005 and 2008. Of 195 gonococcal isolates examined, 29 sequence types (STs) were identified with 3 major circulating strains (ST-1 through ST-3) comprising 52% of all gonococcal isolates studied. The prevalences, persistence, distribution patterns, and clonalities of these isolates strongly suggest that gonorrhea endemicity within this broad geographic region was driven by these 3 circulating strains. ST-1 exhibited a significantly (P = 0.001) higher prevalence throughout the study than did the others, accounting for ∼25% of the tested isolates each year. The spatial distributions of the gonococcal strains indicated that ST-1 in 2007 entered a linear component of the sexual network, reaching the remote north and resulting in the further spread and maintenance of infection. Ciprofloxacin and azithromycin resistances were observed in distantly related gonococcal lineages, clearly indicating the convergent acquisition of these antibiotic-resistant phenotypes. In addition, all ciprofloxacin- and azithromycin-resistant lineages were found at the edges of the minimum spanning tree, far from the major lineages, suggesting that these antibiotic phenotypes were most likely introduced into the province. In contrast, resistance to penicillin was found mostly in the endemic gonococcal lineages, suggesting that penicillin resistance was probably acquired in Saskatchewan as a result of spontaneous mutations in already-established lineages. Tetracycline resistance was present in all STs except one, indicating its ubiquitous nature in the gonococcal population studied.

Emergence of multidrug-resistant, extensively drug-resistant and untreatable gonorrhea

The new superbug Neisseria gonorrhoeae has retained resistance to antimicrobials previously recommended for first-line treatment and has now demonstrated its capacity to develop resistance to the extended-spectrum cephalosporin, ceftriaxone, the last remaining option for first-line empiric treatment of gonorrhea. An era of untreatable gonorrhea may be approaching, which represents an exceedingly serious public health problem. Herein, we review the evolution, origin and spread of antimicrobial resistance and resistance determinants (with a focus on extended-spectrum cephalosporins) in N. gonorrhoeae, detail the current situation regarding verified treatment failures with extended-spectrum cephalosporins and future treatment options, and highlight essential actions to meet the large public health challenge that arises with the possible emergence of untreatable gonorrhea. Essential actions include: implementing action/response plans globally and nationally; enhancing surveillance of gonococcal antimicrobial resistance, treatment failures and antimicrobial use/misuse; and improving prevention, early diagnosis and treatment of gonorrhea. Novel treatment strategies, antimicrobials (or other compounds) and, ideally, a vaccine must be developed.

Genome sequencing of a Neisseria gonorrhoeae isolate of a successful international clone with decreased susceptibility and resistance to extended-spectrum cephalosporins

The recent emergence of Neisseria gonorrhoeae strains with decreased susceptibility to extended-spectrum cephalosporins is a major concern globally. We sequenced the genome of an N. gonorrhoeae multiantigen sequence typing (NG-MAST) ST1407 isolate (SM-3) with decreased susceptibility and resistance to oral extended-spectrum cephalosporins. The isolate was cultured in 2008 in San Francisco, CA, and possessed mosaic penA allele XXXIV, which is associated with an international clone that possesses decreased susceptibility as well as resistance to oral extended-spectrum cephalosporins globally. The genome sequence of strain NCCP11945 was used as a scaffold, and our assembly resulted in 91 contigs covering 2,029,064 bp (91%; >150× coverage) of the genome. Numerous instances of suspected horizontal genetic transfer events with other Neisseria species were identified, and two genes, opa and txf, acquired from nongonococcal Neisseria species, were identified. Strains possessing mosaic penA alleles (n = 108) and nonmosaic penA alleles (n = 169) from the United States and Europe (15 countries), cultured in 2002 to 2009, were screened for the presence of these genes. The opa gene was detected in most (82%) penA mosaic-containing isolates (mainly from 2007 to 2009) but not in any penA nonmosaic isolates. The txf gene was found in all strains containing opa but also in several (18%) penA nonmosaic strains. Using opa and txf as genetic markers, we identified a strain that possesses mosaic penA allele XXXIV, but the majority of its genome is not genetically related to strain SM-3. This implies that penA mosaic allele XXXIV was transferred horizontally. Such isolates also possessed decreased susceptibility and resistance to oral extended-spectrum cephalosporins. These findings support that genetic screening for particular penA mosaic alleles can be a valuable method for tracking strains with decreased susceptibility as well as resistance to oral extended-spectrum cephalosporins worldwide and that screening using only NG-MAST may not be sufficient.

The use of cephalosporins for gonorrhea: an update on the rising problem of resistance

INTRODUCTION

Over the last several years, Neisseria gonorrhoeae has developed decreased susceptibility to extended-spectrum cephalosporins worldwide. Gonococcal antimicrobial surveillance programs in multiple regions have documented the rise in N. gonorrhoeae isolates' minimum inhibitory concentrations to cephalosporins, and the first cases of ceftriaxone treatment failure have been reported. These developments have prompted the use of the term 'superbug' and concerns about the emergence of untreatable gonococcal infections.

AREAS COVERED

Since the publication of the last detailed review of the use of cephalosporins for gonorrhea in 2009, several new developments have occurred, which are detailed in this review. A variety of treatment strategies have been proposed in response to this 'superbug' threat, including increasing the dose or providing multiple doses of cephalosporins, multidrug therapy, rotating therapeutic regimens and individualized treatment based on susceptibility testing.

EXPERT OPINION

A robust public health response is needed that includes better diagnosis and treatment of pharyngeal gonorrhea, improved surveillance of antimicrobial resistance, informed treatment approaches and reduction of the global burden of gonococcal infections.

Using the Neisseria gonorrhoeae multiantigen sequence-typing method to assess strain diversity and antibiotic resistance in San Francisco, California

Urogenital Neisseria gonorrhoeae isolates (266) collected in San Francisco, CA, in 2009 were analyzed for antimicrobial susceptibility and were subsequently genotyped by N. gonorrhoeae multiantigen sequence typing (NG-MAST). Isolates of identical or closely related sequence types were found to possess highly similar phenotypes with regard to drug susceptibility. Isolates containing decreased susceptibility to oral cephalosporins were detected in 2009 and were found to contain the mosaic penA allele (XXXIV) found previously to be associated with decreased susceptibility to cephalosporins. A better understanding of the relationships between phenotypic and genotypic markers for antimicrobial resistance may be helpful to the development of effective surveillance systems for drug-resistant N. gonorrhoeae.

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).

Surveillance of gonococcal antimicrobial susceptibility resulting in early detection of emerging resistance

OBJECTIVES

To undertake laboratory and clinical surveillance of gonococcal antimicrobial susceptibility to various therapeutic agents in Hong Kong, so as to monitor for emerging resistance and to inform on appropriate choice of empirical therapy.

METHODS

Trends in susceptibility of gonococci to ceftriaxone, spectinomycin, ceftibuten and azithromycin were monitored over time. Isolates with reduced susceptibility to oral extended-spectrum cephalosporins were further characterized by detection of the mosaic penA gene and typing by Neisseria gonorrhoeae multi-antigen sequence typing (NG-MAST). Correlation with clinical and epidemiological findings was undertaken on isolates positive for the mosaic penA gene.

RESULTS

Trends in susceptibility of gonococci to ceftriaxone, spectinomycin and ceftibuten remained stable between 2005 and 2010. In 2010, 30.3% of tested strains were not susceptible to azithromycin. The percentage of gonococcal strains harbouring the mosaic penA gene increased from 1.0% during April to December 2010 to 8.2% during January to September 2011 (P < 0.0001). Review of available clinical records showed that, out of 35 patients infected by strains positive for the mosaic penA gene, 30 had laboratory-documented treatment failure.

CONCLUSIONS

This study showed that ceftriaxone and spectinomycin remained effective against gonorrhoea in Hong Kong. There was an alarming increase in strains with reduced susceptibility to oral extended-spectrum cephalosporins associated with clinical treatment failure. One-third of gonococcal isolates were non-susceptible to azithromycin. The need to switch to agents other than oral extended-spectrum cephalosporins for empirical treatment is imminent. Continued surveillance with strain characterization is essential to monitor the effectiveness of currently recommended therapy.

Contrasting Roles of IL-22 and IL-17 in Murine Genital Tract Infection by Neisseria gonorrhoeae

Murine genital tract infection with Neisseria gonorrhoeae has previously been found to induce IL-17 which is important in both recruitment of neutrophils and prompt clearance of the infection. As IL-22 is another Th17-related cytokine that has been implicated in the immune responses in several infection models, we investigated its role in vaginal gonococcal infection of mice. Production of IL-22 was observed in response to stimulation with N. gonorrhoeae in both mouse splenic mononuclear cells and vaginal tissue explants cultured ex vivo. Tissue from mice genetically deficient in IL-22 showed diminished production of IL-6 and the CXC chemokine KC in response to N. gonorrhoeae, whereas IL-17 and the chemokines LIX and MIP-2α were produced to the same extent as in wild-type tissue. IL-22-deficient mice were unexpectedly resistant to genital tract infection with N. gonorrhoeaein vivo, but showed no change in the influx of neutrophils to the site of infection. These results reveal divergent roles for IL-17 and IL-22 in response to gonococcal infection.

Clonally related Neisseria gonorrhoeae isolates with decreased susceptibility to the extended-spectrum cephalosporin cefotaxime in Amsterdam, the Netherlands

From 2006 to 2008, Neisseria gonorrhoeae isolates were identified with decreased susceptibility to the extended-spectrum cephalosporin (ESC) cefotaxime among visitors of the Amsterdam sexually transmitted infections (STI) clinic, the Netherlands. Spread, clonality, and characteristics of 202 isolates were examined using antibiograms, conventional penA mosaic gene PCR, and N. gonorrhoeae multiple-locus variable-number tandem repeat analysis (NG-MLVA). A strictly defined subset was further characterized by N. gonorrhoeae multiantigen sequence typing (NG-MAST) and sequencing of ESC resistance determinants (penA, mtrR, and porB1b). Seventy-four N. gonorrhoeae isolates with a cefotaxime MIC of >0.125 μg/ml (group A), 54 with a cefotaxime MIC of 0.125 μg/ml (group B), and a control group of 74 with a cefotaxime MIC of <0.125 μg/ml (group C) were included. Fifty-three clonally related penA mosaic-positive isolates (penicillin-binding protein 2 type XXXIV) were identified in group A (n = 47 isolates; 64%) and B (n = 6 isolates; 11%). The 53 penA mosaic-positive isolates were predominantly NG-MAST ST1407 (87%) and contained an mtrR promoter A deletion (98%) and porB1b alterations G101K/A102N. All were assigned to the same NG-MLVA cluster that comprised in total 56 isolates. A correlation was found between decreased cefotaxime susceptibility and ST1407 that was highly prevalent among visitors of the Amsterdam STI clinic. The rapid spread of this strain, which also has been identified in many other countries, might be facilitated by high-risk sexual behavior and should be monitored closely to identify potential treatment failure. Quality-assured surveillance of ESC susceptibility on the national and international levels and exploration of new drugs and/or strategies for treatment of gonorrhea are crucial.

High-level cefixime- and ceftriaxone-resistant Neisseria gonorrhoeae in France: novel penA mosaic allele in a successful international clone causes treatment failure

Recently, the first Neisseria gonorrhoeae strain (H041) highly resistant to the expanded-spectrum cephalosporins (ESCs) ceftriaxone and cefixime, which are the last remaining options for first-line gonorrhea treatment, was isolated in Japan. Here, we confirm and characterize a second strain (F89) with high-level cefixime and ceftriaxone resistance which was isolated in France and most likely caused a treatment failure with cefixime. F89 was examined using six species-confirmatory tests, antibiograms (33 antimicrobials), porB sequencing, N. gonorrhoeae multiantigen sequence typing (NG-MAST), multilocus sequence typing (MLST), and sequencing of known gonococcal resistance determinants (penA, mtrR, penB, ponA, and pilQ). F89 was assigned to MLST sequence type 1901 (ST1901) and NG-MAST ST1407, which is a successful gonococcal clone that has spread globally. F89 has high-level resistance to cefixime (MIC = 4 μg/ml) and ceftriaxone (MIC = 1 to 2 μg/ml) and resistance to most other antimicrobials examined. A novel penA mosaic allele (penA-CI), which was penA-XXXIV with an additional A501P alteration in penicillin-binding protein 2, was the primary determinant for high-level ESC resistance, as determined by transformation into a set of recipient strains. N. gonorrhoeae appears to be emerging as a superbug, and in certain circumstances and settings, gonorrhea may become untreatable. Investigations of the biological fitness and enhanced understanding and monitoring of the ESC-resistant clones and their international transmission are required. Enhanced disease control activities, antimicrobial resistance control and surveillance worldwide, and public health response plans for global (and national) perspectives are also crucial. Nevertheless, new treatment strategies and/or drugs and, ideally, a vaccine are essential to develop for efficacious gonorrhea management.