Protocol for the molecular detection of antibiotic resistance mechanisms in Neisseria gonorrhoeae

Direct-qPCR Assay for Coupled Identification and Antimicrobial Susceptibility Testing of Neisseria gonorrhoeae

Multidrug-resistant gonorrhea has become an urgent issue for global public health. As the causative agent of gonorrhea, Neisseria gonorrhoeae, has been progressively developing resistance to nearly all prescribed antimicrobial drugs, monitoring its antimicrobial resistance on a broader scale has become a crucial agenda for effective antibiotic stewardship. Unfortunately, gold standard antimicrobial susceptibility testing (AST) relies on time and labor-intensive phenotypic assays, which lag behind the current diagnostic workflow for N. gonorrhoeae identification based on nucleic acid amplification tests (NAAT). Newer assay technologies based on NAAT can rapidly identify N. gonorrhoeae from clinical specimen but fundamentally lack the capacity to provide phenotypic AST information. Herein, we propose a direct-quantitative PCR (direct-qPCR) assay that enables pathogen-specific identification and phenotypic AST via quantitative measurement of N. gonorrhoeae growth directly from a liquid medium without any sample preprocessing. The assay has an analytical sensitivity of 10² CFU/mL and is highly specific to N. gonorrhoeae in the presence of urogenital flora and clinical swab eluent. We tested seven N. gonorrhoeae strains against three antibiotic agents, penicillin, tetracycline, and ciprofloxacin, and achieved 95.2% category agreement and 85.7% essential agreement with the FDA-approved E-test. The assay presented in this work has the unique ability to identify N. gonorrhoeae and provide phenotypic AST directly from the liquid medium with cell densities as low as 10² CFU/mL, demonstrating an accelerated, sensitive, and scalable workflow for performing both identification and AST of  N. gonorrhoeae.

Performance and Verification of a Real-Time PCR Assay Targeting the gyrA Gene for Prediction of Ciprofloxacin Resistance in Neisseria gonorrhoeae

In the United States, 19.2% of Neisseria gonorrhoeae isolates are resistant to ciprofloxacin. We evaluated a real-time PCR assay to predict ciprofloxacin susceptibility using residual DNA from the Roche Cobas 4800 CT/NG assay. The results of the assay were 100% concordant with agar dilution susceptibility test results for 100 clinical isolates. Among 76 clinical urine and swab specimens positive for N. gonorrhoeae by the Cobas assay, 71% could be genotyped. The test took 1.5 h to perform, allowing the physician to receive results in time to make informed clinical decisions.

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.

Stemming the tide of drug-resistant Neisseria gonorrhoeae: the need for an individualized approach to treatment

Drug-resistant Neisseria gonorrhoeae poses a significant public health challenge. In recent years, gonococci resistant to first- and second-line antibiotics have spread worldwide and new strains have developed that are increasingly resistant to third-generation cephalosporins, which are currently our last line of available treatments. Given the timeline required to develop new drugs or an effective vaccine for N. gonorrhoeae, a top priority is to use the drugs that are available as effectively as possible. Currently, clinical management of gonorrhoea is based upon treatment guidelines informed by international gonococcal antimicrobial susceptibility surveillance programmes. This approach, although currently the most practical, is subject to a number of limitations since surveillance data inherently provide population-level information. As a result, basing treatment guidelines on these data can result in the prescription of more aggressive or broader treatment than is needed by individual patients and hence inadvertently contribute to the development and spread of resistance to important drugs. Clearly, methods are needed that provide patient-specific drug susceptibility information in a time frame that would allow clinicians to prescribe individualized treatment regimens for gonorrhoea. Fortunately, in recent years, there have been a number of advances in the development of rapid methods for characterizing both the genotype and the drug resistance phenotype of N. gonorrhoeae strains. Here, we review these advances and propose additional studies that would help facilitate a transition towards an individualized treatment approach for gonorrhoea.

Evolving gonococcal antimicrobial resistance: research priorities and implications for management

The combination of continually increasing minimum inhibitory concentration values, and outright resistance to the currently available treatments for Neisseria gonorrhoeae, and the paucity of new drugs in the developmental pipeline raises questions that require concentrated research attention at both the microbiologic and programme levels. Here, we describe the need for research related to the mechanisms of resistance, strategies to reduce or prevent the development of resistance and the need for optimal surveillance using local, national and global data.

Current and future treatment options for gonorrhoea

The delivery of effective antimicrobial therapy is essential for public health control of gonorrhoea, in the absence of a suitable vaccine. The antimicrobial agent chosen should have high efficacy and quality, lack toxicity and give >95% success when given empirically. Guidelines, which are informed by surveillance data, are used to aid clinicians in their choice of appropriate agent. Historically, gonorrhoea treatment has been delivered as a single, directly observed dose but this has resulted in failure of successive antimicrobial agents which have been replaced by a new antimicrobial to which resistance has been rare or non-existing. Following the drift towards decreased susceptibility and treatment failure to the extended spectrum cephalosporins, and the lack of 'new' alternative antimicrobials, the threat of difficult to treat or untreatable gonorrhoea has emerged. The challenge of maintaining gonorrhoea as a treatable infection has resulted in national, regional and global response or action plans. This review discusses different approaches to the future treatment of gonorrhoea including; use of ceftriaxone, the injectable cephalosporin at increased dosage; dual antimicrobial therapy; use of drugs developed for other infections and use of older agents, directed by rapid point of care tests, to susceptible infections. Finally, it is considered whether the time is right to readdress the possibility of developing an effective gonococcal vaccine, given the major advances in our understanding of natural infection, molecular pathogenesis and the revolution in molecular biology techniques.

Whole-genome sequencing of bacterial sexually transmitted infections: implications for clinicians

PURPOSE OF REVIEW

Increasingly, genomics is being used to answer detailed clinical questions. Although genome analysis of bacterial sexually transmitted infections (STIs) lags far behind that of many other bacterial pathogens, genomics can reveal previously inaccessible aspects of pathogen biology.

RECENT FINDINGS

Comparative genomic studies on the most common bacterial STI, chlamydia, have revolutionized our understanding of this intracellular bacterium, demonstrating that it undergoes extensive recombination and that the traditional typing schemes can be misleading. Genome projects can also help us to understand the recently observed phenomenon of 'diagnostic escape' seen in both Chlamydia trachomatis and Neisseria gonorrhoeae.

SUMMARY

The routine use of genomics in clinical settings is becoming a reality. For STIs, a primary requirement is an understanding of the diversity of circulating strains and how they change over time. This can help to inform future studies and allow us to address real clinical issues such as outbreak identification, global spread of successful clones and antimicrobial resistance monitoring.

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.