Gonococcal Resistance Markers Were Common, but They Did Not Fully Explain Ciprofloxacin Failure
Neisseria gonorrhoeae remains a moving target for treatment programs that depend on timely susceptibility data. In the Eastern Cape cohort, investigators focused on a central problem in gonorrhoea control: how to characterize circulating strains and resistance determinants when culture-based surveillance is limited and many clinical samples are available only as stored DNA extracts. The answer came from two molecular approaches applied to symptomatic individuals in South Africa — multi-antigen sequence typing and targeted real-time PCR for resistance-associated mutations.
The study analyzed 235 N. gonorrhoeae-positive stored DNA extracts. Sequence typing succeeded in 200 specimens, a recovery rate of 85.1%, and the resulting profiles were not dominated by a single narrow lineage. Instead, diversity was striking, with ST21253 most frequently identified at 26 isolates. In practical terms, that pattern argues against a simple local epidemic driven by one clone and instead points to a broader circulating population that can seed resistance through multiple genetic routes.
One sentence captures the tension in the data: quinolone resistance-associated mutations were common, but they did not perfectly predict ciprofloxacin resistance.
Direct PCR on Specimen DNA Matched Whole-Genome Sequencing Well for Most Targets
The molecular assay targeted mutations in gyrA and parC, the canonical quinolone resistance pathways in gonococci, along with macrolide-linked mutations in the 23S rRNA gene. At least one gyrA or parC mutation was found in 110 of 193 specimens, or 57.0%. Compared with whole-genome sequencing from paired cultured isolates, the assay performed well overall: positive agreement reached 81.2% for parC and 97.0% for gyrA, while negative agreement was 100% and 95.8%, respectively.
Those figures matter because they show that specimen-based molecular surveillance can recover much of the same information that sequencing provides, without requiring every sample to be successfully cultured first. In settings where culture infrastructure is thin or transport conditions are suboptimal, that operational advantage is substantial. Molecular detection from stored material can widen the surveillance net, preserve epidemiologic detail, and reduce the number of missed cases in routine monitoring programs.
The study also compared molecular results with phenotypic susceptibility in paired isolates. Among 65 ciprofloxacin-resistant isolates, resistance-associated mutations were detected in 60 by real-time PCR, or 92.3%, and in 61 by whole-genome sequencing, or 93.8%. Four resistant isolates had no resistance-associated mutation detected by either method. That gap is clinically important because it means the canonical quinolone markers do not capture every resistant phenotype. Resistance can emerge through additional genomic changes, regulatory effects, or mechanisms not covered by the targeted assay, and a narrow marker set will inevitably leave some resistant isolates unclassified.
Macrolide Resistance Remained Rare in This Cohort
Macrolide findings were sparse. The 23S rRNA C2611T mutation appeared in both methods in one isolate, and that isolate had an azithromycin MIC of 8 mg/L. No A2059G mutations were detected. In a programmatic surveillance context, rarity is still useful information: it suggests that the macrolide resistance signal in this cohort was low at the time of sampling, even as quinolone resistance determinants were already well established.
The biological significance is straightforward. Quinolones and macrolides fail through different molecular routes, and the presence of one class of resistance marker does not automatically imply the presence of another. When macrolide targets remain uncommon, they may still be monitored because even isolated appearances can alter empiric treatment choices, especially where dual-therapy strategies have historically depended on azithromycin activity.
Why the Four Unclassified Ciprofloxacin-Resistant Isolates Matter
The most consequential result may be the most uncomfortable one for resistance surveillance: not every resistant isolate was explained by the targeted markers. Four ciprofloxacin-resistant isolates had no detectable RAM by either method. That finding limits any temptation to treat molecular screening as a complete substitute for phenotypic susceptibility testing.
For clinicians and microbiology services, the implication is direct. Molecular assays can accelerate resistance detection and support faster epidemiologic mapping, but they cannot yet replace culture-linked testing in full. A surveillance system built on both methods will be more resilient: molecular testing can broaden reach and speed, while phenotypic testing can catch discordant isolates and the resistance mechanisms that fall outside the assay design. In a pathogen as adaptive as N. gonorrhoeae, that redundancy is not wasteful. It is protective.
The study also strengthens the case for local genomic surveillance in Southern Africa. Eastern Cape isolates showed substantial sequence diversity, which means resistance trends may not be anchored to a single stable background. In such a setting, sequence typing does more than label strains. It helps track transmission networks, detect expansion of successful lineages, and identify whether resistance is being imported, selected locally, or both.
Molecular Surveillance Has Reach, but Its Coverage Is Not Absolute
This preprint sits in the space between laboratory efficiency and clinical certainty. Real-time PCR applied directly to specimen DNA agreed well with whole-genome sequencing for the main quinolone markers, and sequence typing was successful in most samples. Even so, the discordant resistant isolates and the limited predictive value for full ciprofloxacin susceptibility show where molecular surveillance stops short. The assay detected the major resistance biology, but not every resistant outcome.
The authors secured ethics approval from the Research Ethics Committee of the Faculty of Health Sciences at the University of Pretoria, and the work used stored DNA extracts from symptomatic individuals. As a preprint, the findings still await peer review, but the data already sketch a clear microbiologic picture: diverse gonococcal populations, frequent quinolone resistance determinants, and rare macrolide markers in this Eastern Cape cohort.
For treatment programs, the study does not support abandoning phenotypic confirmation. It supports something more operationally useful: a layered surveillance model in which direct molecular testing expands access, whole-genome sequencing refines interpretation, and culture-based susceptibility remains the final arbiter when resistance patterns do not fit the expected script.