Evidence that the gonococcal porA pseudogene is present in a broad range of Neisseria gonorrhoeae strains; suitability as a diagnostic target

An isothermal CRISPR-based diagnostic assay for Neisseria gonorrhoeae and Chlamydia trachomatis detection

IMPORTANCE

A method for Neisseria gonorrhoeae (NG)/Chlamydia trachomatis (CT) detection is developed using multiplex-recombinase polymerase amplification and Cas12a/Cas13a. This method can detect NG and CT simultaneously with high sensitivity and specificity. This method has great potential to be further developed into larger-scale screening and point-of-care testing (POCT).

Development of Cas13a-based assays for Neisseria gonorrhoeae detection and gyrase A determination

Neisseria gonorrhoeae is one of the most common bacterial sexually transmitted infections. The emergence of antimicrobial-resistant N. gonorrhoeae is an urgent public health threat. Currently, the diagnosis of N. gonorrhoeae infection requires expensive laboratory infrastructure, while antimicrobial susceptibility determination requires bacterial culture, both of which are infeasible in low-resource areas where the prevalence of infection is highest. Recent advances in molecular diagnostics, such as specific high-sensitivity enzymatic reporter unlocking (SHERLOCK) using CRISPR-Cas13a and isothermal amplification, have the potential to provide low-cost detection of pathogen and antimicrobial resistance. We designed and optimized RNA guides and primer sets for SHERLOCK assays capable of detecting N. gonorrhoeae via the porA gene and of predicting ciprofloxacin susceptibility via a single mutation in the gyrase A (gyrA) gene. We evaluated their performance using both synthetic DNA and purified N. gonorrhoeae isolates. For porA, we created both a fluorescence-based assay and lateral flow assay using a biotinylated fluorescein reporter. Both methods demonstrated sensitive detection of 14 N. gonorrhoeae isolates and no cross-reactivity with 3 non-gonococcal Neisseria isolates. For gyrA, we created a fluorescence-based assay that correctly distinguished between 20 purified N. gonorrhoeae isolates with phenotypic ciprofloxacin resistance and 3 with phenotypic susceptibility. We confirmed the gyrA genotype predictions from the fluorescence-based assay with DNA sequencing, which showed 100% concordance for the isolates studied. We report the development of Cas13a-based SHERLOCK assays that detect N. gonorrhoeae and differentiate ciprofloxacin-resistant isolates from ciprofloxacin-susceptible isolates. IMPORTANCE Neisseria gonorrhoeae, the cause of gonorrhea, disproportionately affects resource-limited settings. Such areas, however, lack the technical capabilities for diagnosing the infection. The consequences of poor or absent diagnostics include increased disease morbidity, which, for gonorrhea, includes an increased risk for HIV infection, infertility, and neonatal blindness, as well as an overuse of antibiotics that contributes to the emergence of antibiotic resistance. We used a novel CRISPR-based technology to develop a rapid test that does not require laboratory infrastructure for both diagnosing gonorrhea and predicting whether ciprofloxacin can be used in its treatment, a one-time oral pill. With further development, that diagnostic test may be of use in low-resource settings.

Development of Cas13a-based Assays for Neisseria gonorrhoeae Detection and Gyrase A Determination

Background

Neisseria gonorrhoeae is one of the most common bacterial sexually transmitted infections. The emergence of antimicrobial-resistant N. gonorrhoeae is an urgent public health threat. Currently, diagnosis of N. gonorrhoeae infection requires expensive laboratory infrastructure, while antimicrobial susceptibility determination requires bacterial culture, both of which are infeasible in low-resource areas where prevalence is highest. Recent advances in molecular diagnostics, such as Specific High-sensitivity Enzymatic Reporter unLOCKing (SHERLOCK) using CRISPR-Cas13a and isothermal amplification, have the potential to provide low-cost detection of pathogen and antimicrobial resistance.

Methods and Results

We designed and optimized RNA guides and primer-sets for SHERLOCK assays capable of detecting N. gonorrhoeae via the por A gene and of predicting ciprofloxacin susceptibility via a single mutation in the gyrase A ( gyr A) gene. We evaluated their performance using both synthetic DNA and purified N. gonorrhoeae isolates. For por A, we created both a fluorescence-based assay and lateral flow assay using a biotinylated FAM reporter. Both methods demonstrated sensitive detection of 14 N. gonorrhoeae isolates and no cross-reactivity with 3 non-gonococcal Neisseria isolates. For gyr A, we created a fluorescence-based assay that correctly distinguished between 20 purified N. gonorrhoeae isolates with phenotypic ciprofloxacin resistance and 3 with phenotypic susceptibility. We confirmed the gyr A genotype predictions from the fluorescence-based assay with DNA sequencing, which showed 100% concordance for the isolates studied.

Conclusion

We report the development of Cas13a-based SHERLOCK assays that detect N. gonorrhoeae and differentiate ciprofloxacin-resistant isolates from ciprofloxacin-susceptible isolates.

High-Resolution Melting Analysis to Detect Antimicrobial Resistance Determinants in South African Neisseria gonorrhoeae Clinical Isolates and Specimens

BACKGROUND

Antimicrobial resistance is limiting treatment options for Neisseria gonorrhoeae infections. To aid or replace culture and the syndromic management approach, molecular assays are required for antimicrobial susceptibility testing to guide appropriate and rapid treatment.

OBJECTIVE

We aimed to detect single-nucleotide polymorphisms and plasmids associated with antimicrobial resistance from N. gonorrhoeae isolates from a clinic population in South Africa, using real-time PCR as a rapid test for AMR detection.

METHODS

N. gonorrhoeae isolates, from female and male patients presenting for care at a sexually transmitted infections clinic in Durban, South Africa, were analysed using phenotypic and genotypic methods for identification and antibiotic susceptibility testing (AST). Real-time PCR and high-resolution melting analysis were used to detect porA pseudogene (species-specific marker) and resistance-associated targets. Whole-genome sequencing was used as the gold standard for the presence of point mutations.

RESULTS

The real-time porA pseudogene assay identified all N. gonorrhoeae-positive isolates and specimens. Concordance between molecular detection (real-time PCR and HRM) and resistance phenotype was ≥92% for bla TEM (HLR penicillin), rpsJ_V57M (tetracycline), tetM (tetracycline), and gyrA_S91F (ciprofloxacin). Resistance determinants 16SrRNA_C1192U (spectinomycin), mtrR_G45D (azithromycin), and penA_D545S, penA_mosaic (cefixime/ceftriaxone) correlated with the WHO control isolates.

CONCLUSIONS

Eight resistance-associated targets correlated with phenotypic culture results. The porA pseudogene reliably detected N. gonorrhoeae. Larger cohorts are required to validate the utility of these targets as a convenient culture-free diagnostic tool, to guide STI management in a South African population.

Development and application of Cas13a-based diagnostic assay for Neisseria gonorrhoeae detection and azithromycin resistance identification

BACKGROUND

Gonorrhoea, caused by Neisseria gonorrhoeae, has spread worldwide. Strains resistant to most antibiotics, including ceftriaxone and azithromycin, have emerged to an alarming level. Rapid testing for N. gonorrhoeae and its antimicrobial resistance will therefore contribute to clinical decision making for early diagnosis and rational drug use.

METHODS

A Cas13a-based assay (specific high-sensitivity enzymatic reporter unlocking; SHERLOCK) was developed for N. gonorrhoeae detection (porA gene) and azithromycin resistance identification (A2059G, C2611T). Assays were evaluated for sensitivity with purified dsDNA and specificity with 17 non-gonococcal strains. Performance of SHERLOCK (porA) was compared with Roche Cobas 4800 using 43 urine samples. Identification of azithromycin resistance mutations (A2059G, C2611T) was evaluated using a total of 84 clinical isolates and 18 urine samples. Lateral flow was tested for this assay as a readout tool. Moreover, we directly assayed 27 urethral swabs from patients with urethritis to evaluate their status in terms of N. gonorrhoeae infection and azithromycin resistance.

RESULTS

The SHERLOCK assay was successfully developed with a sensitivity of 10 copies/reaction, except 100 copies/reaction for A2059G, and no cross-reaction with other species. Comparison of the SHERLOCK assay with the Cobas 4800 revealed 100% concordance within 18 positive and 25 negative urine samples. Of the 84 isolates, 21 strains with azithromycin resistance mutations were distinguished and further verified by sequencing and MIC determination. In addition, 62.96% (17/27) strains from swab samples were detected with no mutant strains confirmed by sequencing.

CONCLUSIONS

The SHERLOCK assay for rapid N. gonorrhoeae detection combined with azithromycin resistance testing is a promising method for application in clinical practice.

Solithromycin versus ceftriaxone plus azithromycin for the treatment of uncomplicated genital gonorrhoea (SOLITAIRE-U): a randomised phase 3 non-inferiority trial

BACKGROUND

Antibiotic-resistant gonorrhoea represents a global public health threat, and new therapies are needed. We aimed to compare the efficacy and safety of solithromycin, a fourth generation macrolide, with ceftriaxone plus azithromycin for the treatment of gonorrhoea.

METHODS

We did an open-label, multicentre, non-inferiority trial of patients aged 15 years or older with uncomplicated untreated genital gonorrhoea at two sites in Australia and one site in the USA. Patients were randomly assigned (1:1) to receive single dose oral solithromycin 1000 mg or intramuscular ceftriaxone 500 mg plus oral azithromycin 1000 mg. Neisseria gonorrhoeae cultures were obtained at baseline and test of cure (day 7 ± 2). The primary outcome was the proportion of patients with eradication of genital N gonorrhoeae based on culture at test of cure, assessed in the microbiological intention-to-treat (mITT) population, which included all randomly assigned patients who received any dose of study drug and had a positive genital culture for N gonorrhoeae at baseline. Non-inferiority of solithromycin was to be concluded if the lower limit of the 95% CI for the between-group differences was greater than -10%. Safety was analysed in all patients who received any dose of study drug. This trial is registered with ClinicalTrials.gov, number NCT02210325.

FINDINGS

Between Sept 3, 2014, and Aug 27, 2015, 262 patients were randomly assigned and 261 received treatment (130 in the solithromycin group and 131 in the ceftriaxone plus azithromycin group). In the mITT population, 99 (80%) of 123 patients in the solithromycin group and 109 (84%) of 129 patients in the ceftriaxone plus azithromycin group had N gonorrhoeae eradication at test of cure (difference -4·0%, 95% CI -13·6 to 5·5), thus solithromycin did not meet the criterion for non-inferiority at the prespecified -10% margin. The frequency of adverse events was higher in the solithromycin group than the ceftriaxone plus azithromycin group (69 [53%] of 130 patients vs 45 [34%] of 131 patients), the most common of which were diarrhoea (31 [24%] of 130 patients vs 20 [15%] of 131 patients), and nausea (27 [21%] of 130 patients vs 15 [11%] of 131 patients).

INTERPRETATION

Solithromycin as a single 1000 mg dose is not a suitable alternative to ceftriaxone plus azithromycin as first-line treatment for gonorrhoea. If insufficient duration of solithromycin exposure at the infection site in a subset of individuals was the reason for treatment failures, this might be adequately addressed with dose adjustment. However, any further trials with longer dosing need to consider the potential risk of gastrointestinal effects and liver enzyme elevations.

FUNDING

Cempra Pharmaceuticals.

Multiplex nested polymerase chain reaction targeting multiple genes for the detection of Neisseria gonorrhoeae and Chlamydia trachomatis in genitourinary specimens

Objectives:

The objective of this study was to design and evaluate a novel multiplex nested polymerase chain reaction (PCR) protocol for simultaneous detection of Neisseria gonorrhoeae and Chlamydia trachomatis in genitourinary specimens obtained from symptomatic patients clinically suspected of sexually transmitted infections (STIs), targeting two different genes each for these pathogens.

Materials and Methods:

A total of 116 genitourinary specimens were collected from men (n = 12) and women (n = 104). Direct microscopy, culture isolation, and antimicrobial susceptibility testing for N. gonorrhoeae were performed. Multiplex nested PCR was performed on clinical samples using novel designed primers targeting porA pseudogene and opa gene of N. gonorrhoeae and momp gene and cryptic plasmid of C. trachomatis simultaneously. DNA sequence analysis of nested PCR amplicons for each of four gene targets was carried out for the validation of in-house designed primers and PCR protocol.

Results:

A total of 51.72% (60/116) patients were detected to have either of the two STIs. About 35.35% (41/116) of patients were positive for C. trachomatis and 33.62% (39/116) for N. gonorrhoeae by employing multiplex nested PCR. Coinfection with N. gonorrhoeae and C. trachomatis was detected in 17.24% (20/116) patients. 31.5% endocervical swabs (n = 54), 64.4% speculum-assisted high vaginal swabs (n = 45), and 80% self-collected vaginal swabs (n = 5) were detected positive for either of two STIs.

Conclusions:

The multiplex nested PCR protocol designed and employed in the present study may be used in the diagnosis and management of both symptomatic as well as asymptomatic cases of N. gonorrhoeae and C. trachomatis, particularly among high-risk groups.

Molecular test for chlamydia and gonorrhoea used at point of care in remote primary healthcare settings: a diagnostic test evaluation

OBJECTIVES

A new molecular test for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) (GeneXpert CT/NG) has been demonstrated to be as accurate as conventional nucleic acid amplification tests (NAAT), but performance has not been evaluated in routine primary care, performed at the point of care by clinicians. We aimed to examine its diagnostic performance when used by clinicians in remote community health services in Australia with high prevalences of CT and NG infection. The trial was registered with the Australian and New Zealand Clinical Trials Registry (#12613000808741) METHODS: At 12 health services, training was provided to 99 clinicians in the use of the GeneXpert CT/NG assay who tested specimens from all patients undergoing STI screening. Specimens were also sent in parallel for conventional laboratory-based NAATs and the concordance of results was evaluated.

RESULTS

Clinicians conducted 2486 tests: CT concordance was 99.4% (95% CI 99.1 to 99.7) with a positive concordance of 98.6% (95% CI 95.9 to 99.7) and negative concordance of 99.5% (95% CI 99.1 to 99.8); NG concordance was 99.9% (95% CI 99.7 to 100.0) with a positive concordance of 100.0% (95% CI 97.5 to 100.0) and negative concordance of 99.9% (95% CI 99.7 to 100.0).

CONCLUSIONS

In this first study reporting routine point-of-care use of GeneXpert CT/NG by primary care clinicians, we found excellent concordance with conventional NAATs. The use of the GeneXpert CT/NG at the point of care could potentially transform management and control of these infections in many endemic settings, including low/middle-income countries.

Loop-mediated isothermal amplification of Neisseria gonorrhoeae porA pseudogene: a rapid and reliable method to detect gonorrhea

BACKGROUND AND OBJECTIVE

Gonorrhea is a sexually transmitted disease caused by the bacterium Neisseria gonorrhoeae. Rapid detection is crucial for effective prevention and treatment. This study developed and tested a low-cost effective method for detecting N. gonorrhoeae, especially in developing countries.

METHODS

DNA from a N. gonorrhoeae standard strain, as well as from 26 genital secretion samples of gonorrhea patients, were isolated and used for loop-mediated isothermal amplification (LAMP) assay, which was conducted using either an automatic real-time PCR analyzer or a water bath. The amplified porA pseudogene sequence was compared with the NCBI database and the LAMP results were compared with that of the traditional culture method for its sensitivity and specificity.

RESULTS

LAMP was able to detect Neisseria DNA at a concentration as low as 1 pg/µL (1 × 10³ CFU/mL cells). The LAMP assay results obtained using an automatic real-time PCR analyzer was similar to that of the water bath. Relative to traditional culture, the sensitivity and specificity of the LAMP assay were 94.7 and 85.7%, respectively.

CONCLUSION

LAMP was sensitive and reliable for detecting the porA gene of N. gonorrhoeae. It could be used as a rapid, low cost, and effective method for detecting N. gonorrhoeae.

A multicentre double-blind randomised controlled trial evaluating the efficacy of daily use of antibacterial mouthwash against oropharyngeal gonorrhoea among men who have sex with men: the OMEGA (Oral Mouthwash use to Eradicate GonorrhoeA) study protocol

BACKGROUND

Gonorrhoea is one of the most common sexually transmissible infections in men who have sex with men (MSM). Gonorrhoea rates have increased substantially in recent years. There is concern that increasing gonorrhoea prevalence will increase the likelihood of worsening antibiotic resistance in Neisseria gonorrhoeae. A recent randomised controlled trial (RCT) demonstrated that a single-dose of mouthwash has an inhibitory effect against oropharyngeal gonorrhoea. We are conducting the first RCT to evaluate whether daily use of mouthwash could reduce the risk of acquiring oropharyngeal gonorrhoea.

METHODS/DESIGN

The OMEGA (Oral Mouthwash use to Eradicate GonorrhoeA) study is a double-blind RCT and will be conducted at several sexual health clinics and high caseload General Practice (GP) clinics in Melbourne and Sydney, Australia. A total of 504 MSM attending the participating sites will be recruited. Participants will be randomised to either using 'Study mouthwash A' or 'Study mouthwash B' for 12 weeks. Study mouthwash A was inhibitory against N. gonorrhoeae in vitro, whereas study mouthwash B was not. Participants will be instructed to rinse and gargle the study mouthwash for 60 seconds every day. The primary outcome is the proportion of participants with oropharyngeal gonorrhoea detected by nucleic acid amplification test by 12 weeks.

DISCUSSION

The results from this trial may provide a novel way to reduce gonorrhoea prevalence and transmission without the use of antibiotics that may be associated with development of resistance. If shown to be effective, the widespread use of mouthwash will reduce the prevalence of oropharyngeal gonorrhoea, which plays key role in driving the emergence of gonococcal antimicrobial resistance through DNA exchange with oral commensal bacteria. The anticipated net effect will be interruption of onward transmission of N. gonorrhoeae within high density sexual networks within MSM populations.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12616000247471 , registered on 23rd February 2016.

Neisseria gonorrhoeae Bacterial DNA Load in the Pharynges and Saliva of Men Who Have Sex with Men

Neisseria gonorrhoeae can be cultured in the saliva of individuals with pharyngeal gonorrhea. The aim of this study was to quantify the gonococcal bacterial DNA loads in the pharynges and saliva among men who have sex with men (MSM) with untreated pharyngeal gonorrhea. Untreated MSM who tested positive for pharyngeal gonorrhea by culture and returned for antibiotic treatment within 14 days at the Melbourne Sexual Health Centre between October 2014 and March 2015 were eligible for this study. The gonococcal bacterial DNA load was measured using real-time quantitative PCR. The median gonococcal bacterial DNA loads in the pharynges and saliva were calculated and compared to culture positivity using the Mann-Whitney U test. A total of 33 men were included in this study. The median gonococcal bacterial DNA load did not differ between the pharynges in men who were culture positive (2.5 × 10(5) copies/swab) and culture negative (2.9 × 10(4) copies/swab) (P = 0.166) and the saliva (culture positive, 2.2 × 10(5) copies/ml; culture negative, 2.7 × 10(5) copies/ml) (P = 0.499). The bacterial DNA load in the pharynges (P = 0.695) and saliva (P = 0.969) did not differ between who men returned for treatment within 7 days and those who returned 8 to 14 days later. Substantial gonococcal bacterial DNA loads were detected in both saliva and pharynges among MSM with pharyngeal gonorrhea. These findings suggest that gonorrhea can be transmitted via sexual practices involving exposure to saliva, such as oroanal practices (rimming) and saliva use as a lubricant for anal sex.

Molecular epidemiology of Neisseria gonorrhoeae using multi-antigen sequence typing and pulse-field gel electrophoresis in highly endemic Western Australian populations

Background

The remote and indigenous populations of Western Australia (WA) have one of the highest notification rates of gonorrhoea in the world. Despite this, the low rate of antimicrobial resistance in Neisseria gonorrhoeae from these regions permits the use of amoxycillin as empirical therapy. We describe the first molecular epidemiological study of gonococci isolated from this population using two different typing platforms.

Methods

Pulse-field gel electrophoresis (PFGE), Neisseria gonorrhoeae multi-antigen sequence typing (NG-MAST) and antimicrobial susceptibility tests were performed on 128 consecutive N. gonorrhoeae isolates cultured between January 2011 and December 2013. To highlight clusters isolates were evaluated based on their tbpB sequence types.

Results

No predominant NG-MAST or PFGE types were found. A total of 67 distinct PFGE pulsotypes were identified amongst the 128 isolates in this study with 20 PFGE pulsotypes representing 78 isolates. A total of 59 NG-MAST sequence types were found, represented by 45 porB alleles and 28 tbpB alleles with 13 tbpB genomogroups from 45 NG-MAST sequence types. TbpB genomogroup 29, represented by 45 isolates, was by far the most common genomogroup overall.

Conclusions

Results from this study suggest that gonococcal epidemiology in WA is quite different between remote regions and major population centres and, in some cases, geographically restricted. It is likely that isolates originating from endemic regions of WA mostly represent independent, small sexual networks with an infrequent interchange between other communities and regions. Given the high rate of antimicrobial resistance elsewhere in Australia, ongoing surveillance is essential to ensure the enduring efficacy of amoxycillin empiric use in the remote regions of WA.

Purification of DNA eluates from the ProbeTec GC Q(x) assay on BD Viper™ XTR allows for further analysis and confirmation of gonorrhea

Low positive predictive values of Neisseria gonorrhoeae nucleic acid amplification tests in low-prevalence populations are a major challenge for accurate diagnostics. It is therefore necessary to verify all positive N. gonorrhoeae results with a different assay and target gene, preferably using the same sample. The BD ProbeTec™ Q(x) Collection Kit for Endocervical or Lesion Specimens, which is recommended for BD Viper™ XTR, is incompatible with other commercial platforms. Therefore, a confirmatory PCR has not been available for samples received on this transport medium. To be able to verify results from these samples with another assay, our objective was to establish a procedure for using the DNA eluates from BD Viper™ XTR for further analysis. DNA eluates from BD Viper™ XTR were collected and analyzed in two in-house confirmatory real-time PCRs targeting the porA pseudogene and the opa multicopy gene. BD Viper™ XTR DNA eluates were analyzed directly and also after purification with the nucleic acid extraction system NucliSENS® easyMag®. Purification of BD Viper™ XTR DNA eluates with the nucleic acid extraction system NucliSENS® easyMag® provided a sensitivity of the in-house PCR comparable to BD Viper™. With the inclusion of two target genes in the confirmatory PCR, specific and reliable verification of results were obtained. This study presents a simple, inexpensive procedure which allows for rapid verification of gonorrhea from samples received on the BD ProbeTec™ Q(x) Collection Kit for Endocervical or Lesion Specimens.

Multiplex bead suspension array for screening Neisseria gonorrhoeae antibiotic resistance genetic determinants in noncultured clinical samples

The increasing threat of antibiotic-resistant Neisseria gonorrhoeae highlights the need for new diagnostic options. A high-throughput multiplex bead suspension array assay was developed for profiling 29 N. gonorrhoeae genomic mutations and 2 plasmid genes conferring resistance to 6 antimicrobial agents: penicillin, ciprofloxacin, cefixime, tetracycline, azithromycin, and spectinomycin. The three steps of this assay include amplification of 12 N. gonorrhoeae chromosomal and plasmid loci, multiplex allele-specific primer extension reaction, and multiplex bead suspension array detection. Antibiotic resistance genetic determinants were identified successfully in 239 cervicovaginal N. gonorrhoeae-positive noncultured swab samples. This molecular assay can be used for detection of gonococci in clinical specimens, molecular typing, mutation profiling, and predictive assessment of N. gonorrhoeae susceptibility to antibiotics without the need for culture.

Evaluation of an opa gene-based nucleic acid amplification test for detection of Neisseria gonorrhoeae in urogenital samples in North India

Due to the poor positive predictive value of nucleic acid amplification tests (NAATs) for gonorrhoea when applied to a low-prevalence setting, current guidelines recommend the use of supplementary polymerase chain reaction (PCR) targeting a different gene for confirmation of true positives in urogenital specimens. This study sought to standardize and evaluate performance of an in-house opa gene-based PCR assay for gonorrhoea compared to assays targeting the porA pseudogene and 16S rRNA gene. Four hundred samples (300 endocervical, 100 urethral swabs) from patients attending STD clinics in New Delhi, India were used. The sensitivity, specificity, positive predictive value and negative predictive value of the opa-based PCR were 100%, 97·9%, 89·5% and 100%, respectively. In females, the use of NAATs provided enhanced diagnosis of gonorrhoea.

Is it time to move to nucleic acid amplification tests screening for pharyngeal and rectal gonorrhoea in men who have sex with men to improve gonorrhoea control?

The use of nucleic acid amplification tests (NAAT), as well as or in preference to culture for non-genital sites is now recommended both in Australia and overseas because of their greater sensitivity and improved specificity. A survey of 22 Australian sexual health clinics who each year test over 14500 men who have sex with men (MSM) show that culture remains the predominate method for detecting gonorrhoea at pharyngeal (64%) and rectal (73%) sites. This editorial discusses the potential disadvantages of using culture over NAAT in relation to optimal gonorrhoea control among MSM and advocates that significantly improved control would be achieved by moving to NAAT with the proviso that culture samples are taken wherever possible on NAAT-positive samples and from clients with urethritis to ensure continued surveillance for antimicrobial resistance.

Evaluation of the Abbott RealTime CT/NG assay in comparison to the Roche Cobas Amplicor CT/NG assay

Several commercial methods exist for the molecular detection of Chlamydia trachomatis and Neisseria gonorrhoeae in clinical samples. Here we evaluated the performance characteristics of the newly FDA-cleared Abbott RealTime CT/NG assay (where "CT" stands for Chlamydia trachomatis and "NG" stands for Neisseria gonorrhoeae) that uses the automated m2000 molecular platform. Results were compared to those of the Roche Cobas Amplicor CT/NG assay. A total of 926 cervical swab, 45 female urine, 6 male urethral swab, and 407 male urine specimens from 1,384 patients were examined. After resolving all Roche N. gonorrhoeae-positive results with two additional real-time PCR assays, we found that the agreement between the assays was excellent. For urine samples, there was 99.6% positive agreement and 97.7% negative agreement for C. trachomatis, and for male urine samples, there was 100% positive agreement and 99.7% negative agreement for N. gonorrhoeae. For cervical swab samples, there was 98.8% positive agreement and 98.5% negative agreement for C. trachomatis, and there was 96.6% positive agreement and 99.8% negative agreement for N. gonorrhoeae. In limiting dilution analyses, we found that the Abbot assay was more sensitive than the Roche assay for both C. trachomatis and N. gonorrhoeae. In addition, there appeared to be an enhanced ability of the Abbott assay to detect dual infections, especially in the presence of large amounts of N. gonorrhoeae and small amounts of C. trachomatis organisms. In summary, we conclude that the Abbott RealTime CT/NG assay is an accurate and automated new addition to the available testing options for C. trachomatis and N. gonorrhoeae.

Design of a multiplex PCR assay for the simultaneous detection and confirmation of Neisseria gonorrhoeae

OBJECTIVES

To improve the detection of Neisseria gonorrhoeae by designing a multiplex PCR assay using two N gonorrhoeae-specific genes as targets, thereby providing detection and confirmation of a positive result simultaneously.

METHODS

PCR primers were designed to detect two N gonorrhoeae genes, namely porA and pgi1. Primers for an internal control targeting the ompW gene of Vibrio cholerae were also designed and incorporated in the assay. The DNA of 45 clinical isolates including 33 N gonorrhoeae isolates, seven non-gonococcal Neisseria species, and five non-Neisseria species was tested using the multiplex PCR assay.

RESULTS

All 33 N gonorrhoeae isolates were successfully detected by the assay and none of the non-gonococcal isolates was detected. The assay showed a sensitivity and specificity of 100%, and a limit of detection of 1.25 ng of DNA.

CONCLUSION

This multiplex PCR assay offers a sensitive and specific assay suitable for the detection of N gonorrhoeae, and offers real potential for diagnostic use.

Comparison of microscopy, culture and in-house PCR and NASBA assays for diagnosis of Neisseria gonorrhoeae in Russia

This study aimed to assess the laboratory diagnosis of Neisseria gonorrhoeae in St. Petersburg, Russia. In total, 334 consecutive symptomatic patients were enrolled. Cervical and urethral specimens from women (n=286) and urethral specimens from men (n=48) were analyzed by microscopy, culture and two in-house NAATs, i.e. polymerase chain reaction (PCR) and nucleic acid sequence-based amplification (NASBA), developed in Russia. All N. gonorrhoeae-positive samples were confirmed using porA pseudogene and 16S rRNA gene sequencing. All methods displayed 100% specificity, i.e. positive predictive values of 100%. Compared to the PCR (most sensitive method in the present study), in women the sensitivity of both microscopy and culture was 31.8%, and that of NASBA was 90.9%. In men, microscopy, culture and NASBA displayed a sensitivity of 75%, 50% and 100%, respectively. The negative predictive values of microscopy, culture, and NASBA were 97.3%, 97.3%, and 99.6% in women, and 97.8%, 95.7%, and 100% in men, respectively. According to the PCR, the prevalences of N. gonorrhoeae were 4.5% (women) and 8.3% (men). In conclusion, both the investigated Russian NAATs displayed a high sensitivity and specificity. However, in general the diagnosis of gonorrhoea in Russia is suboptimal and crucially requires validation, improvements and quality assurance.

A duplex Neisseria gonorrhoeae real-time polymerase chain reaction assay targeting the gonococcal porA pseudogene and multicopy opa genes

Cross-reactions of gonococcal nucleic acid amplification tests (NAATs) with commensal Neisseria strains are well documented. Recent data now indicate that sequence-related false-negative results can occur in gonococcal NAATs, whereby target sequences either are absent or contain several mutations. In this study, a duplex Neisseria gonorrhoeae real-time polymerase chain reaction (PCR) (NGduplex) assay targeting the gonococcal porA pseudogene and multicopy opa genes was developed. The NGduplex was evaluated by testing 596 clinical specimens, including 292 urogenital specimens and 304 throat swab specimens. The results were compared with those obtained using a consensus reference standard comprising 3 monoplex real-time PCR assays. The results show that the NGduplex assay is highly suitable for routine screening for gonorrhea, providing an overall clinical sensitivity and specificity of 100% and 99.3%, respectively, for both urogenital and throat swab specimens. In addition, the 2-target system of the NGduplex assay decreases the potential for sequence-related false-negative results and can provide simultaneous confirmation of positive results.