Trends in population structure, antimicrobial susceptibility and resistance determinants of Neisseria gonorrhoeae isolates from surveillance in the Kanto region, Japan, 2017-2023

Abstract
Objectives
The spread of antimicrobial-resistant Neisseria gonorrhoeae has limited treatment options. To monitor trends in population structure, antimicrobial susceptibility rates and resistant determinants of gonococcus isolated from patients, we collected longitudinal isolates and performed AST and molecular analyses.

Methods
Of 985 gonococcus isolates obtained from clinical specimens submitted by health care institutions in the Kanto region of Japan between 2017 and 2023, one isolate per patient per year was eligible, and up to 50 isolates per year were randomly selected. A total of 349 isolates were analysed. MICs were determined by the agar dilution method. Multilocus sequence typing and N. gonorrhoeae sequence typing for antimicrobial resistance (NG-STAR) were performed using a high-throughput typing method based on multiplex PCR amplicon sequencing on the MiSeq (Illumina) platform.

Results
Over this study period, 29 sequence types (STs) were identified. Only one ceftriaxone non-susceptible strain—harbouring mosaic penA 60.001 and belonging to ST1903—was found in 2017. A ciprofloxacin-susceptible lineage belonging to ST9362, lacking quinolone resistance-determining region mutations, was sporadically predominant in 2018 and 2023. The susceptibility rate to azithromycin remained ≥86% throughout the study period. There was a clear association between lineage and carriage of antimicrobial resistance determinants.

Conclusions
Ceftriaxone remains a reliable first-line treatment option for gonorrhoea. Ongoing surveillance is essential to detect emerging fluoroquinolone-susceptible lineages that may inform future treatment strategies.