Antimicrobial resistance (AMR) in Neisseria gonorrhoeae is recognized as a major global public health concern, particularly because resistance to the last widely used monotherapy, ceftriaxone, has been reported in several Asian countries. This investigation aimed to examine AMR among gonococcal isolates collected at the Bangrak STIs Center in Bangkok, Thailand, over the period 2018–2023 and to apply whole-genome sequencing (WGS) to isolates resistant to ceftriaxone, cefixime and/or azithromycin.
Genital and extragenital swabs were collected from males, females and transgender women attending the Bangrak STIs Center and cultured for Neisseria gonorrhoeae. Antimicrobial susceptibility testing for five antimicrobials was performed using Etest with interpretation according to EUCAST breakpoints (v16.0). Ciprofloxacin susceptibility was assessed using the disc diffusion method. Isolates that were resistant to ceftriaxone, cefixime and/or azithromycin underwent whole-genome sequencing on an Illumina NextSeq 550 platform to identify genetic determinants associated with resistance.
Between 2018 and 2023, a total of 765 gonococcal isolates were cultured from 739 individual patients at the Bangrak STIs Center. Measured resistance prevalences across the study period were: ceftriaxone 0.5%, cefixime 0.8%, azithromycin 1.7%, tetracycline 83.7% and ciprofloxacin 95.7%.
Ceftriaxone-resistant isolates were first identified in 2023 (three isolates, representing 1.2% of isolates that year), and all ceftriaxone-resistant isolates were also resistant to cefixime. Additional cefixime-resistant isolates were detected earlier, including two isolates in 2022 (1.4% that year). Azithromycin resistance first appeared in 2020 (one isolate, 0.9% that year) and increased in subsequent years, reaching nine isolates (3.7%) in 2023. These findings indicate the emergence and apparent increase of resistance to agents that are critical for current gonorrhoea treatment strategies.
WGS was performed on isolates resistant to ceftriaxone, cefixime and/or azithromycin. All ceftriaxone-resistant isolates were found to contain the penA-60.001 allele. Cefixime resistance in addition involved other penA alleles, specifically penA-34.019 and penA-10.001, indicating different mosaic or altered penA variants contributing to reduced susceptibility or resistance to extended-spectrum cephalosporins. All azithromycin-resistant isolates carried mutations in the 23S rRNA gene and/or had mosaic or semi-mosaic forms of MtrD, a subunit of the MtrCDE efflux pump, implicating target-site modification and enhanced efflux as mechanisms behind azithromycin resistance.
The study documents the emergence of resistance to ceftriaxone, cefixime and azithromycin among gonococcal strains circulating in Bangkok, Thailand, with evidence that these resistances are increasing over the study period. The concurrence of ceftriaxone and cefixime resistance and the detection of azithromycin-resistant isolates with known genetic determinants are particularly concerning because these drugs represent last options for monotherapy or components of dual therapy.
The authors emphasize the need to strengthen national culture-based and genomic surveillance to detect and prevent the spread of multidrug-resistant (MDR) and extensively drug-resistant (XDR) gonococcal strains in Thailand and beyond. They also note the importance of implementing novel oral treatments, specifically zoliflodacin and gepotidacin, as part of the response to emerging resistance.
The abstract reports aggregate culture and resistance results and summarizes key genomic findings, but does not provide detailed demographic breakdowns, the exact number of isolates undergoing WGS, or additional laboratory or clinical metadata in the abstract itself. These details were not reported in the source abstract.
Local surveillance at a major STI clinic identified low but emerging rates of resistance to critical antimicrobials, including ceftriaxone and azithromycin.
High prevalences of tetracycline and ciprofloxacin resistance confirm limited utility of those agents for empirical gonorrhoea therapy in this setting.
WGS identified established genetic markers associated with cephalosporin and azithromycin resistance (penA alleles, 23S rRNA mutations, mosaic/semi-mosaic MtrD), supporting laboratory-based genomic approaches for tracking AMR.
Strengthened culture-based surveillance, genomic characterization, and adoption of novel antimicrobials are recommended to mitigate spread of MDR/XDR strains.