Sustained transmission advantage of ceftriaxone-resistant Neisseria gonorrhoeae in Tianjin, China: a retrospective genomic surveillance study

OBJECTIVES: The global dissemination of ceftriaxone-resistant Neisseria gonorrhoeae, especially penA-60.001-associated clones, poses a critical public health threat. We investigated antimicrobial resistance, genomic clones and clades, and molecular transmission networks among 188 N. gonorrhoeae isolates collected from 14 medical institutions (2021-2023) in Tianjin, China, to identify the evolutionary drivers and transmission dynamics contributing to the persistent spread of ceftriaxone resistance. METHODS: Susceptibility to six antimicrobials was determined by agar dilution, and whole-genome sequencing was performed using the Illumina NovaSeq platform. MLST and NG-STAR sequence types were derived from genome sequences. Phylogenomic and molecular network analyses included isolates from Tianjin, FC428, and eight previously reported FC428-related isolates from China. RESULTS: Ceftriaxone resistance was detected in 26% (49/188) of isolates (MIC 0.25-4 mg/L), mainly associated with MLST ST1903 and NG-STAR ST1143 or ST233. Among ceftriaxone-resistant isolates, 82% (40/49) harboured penA-60.001. Phylogenomic analysis showed that 83% (33/40) of penA-60.001 isolates clustered within clade 6 (MLST ST1903 and ST13943), and 10% (4/40) belonged to clade 4.2 (MLST ST8123). MLST ST13943 appeared to have evolved within the same genomic clade as ST1903. Three penA-60.001 isolates (MLST ST7367, ST12514, and ST1600) were distributed in clades 9 and 10.1, suggesting possible acquisition of penA-60.001 into distinct genetic backgrounds. Molecular network analysis demonstrated that ceftriaxone resistance was independently associated with inclusion in the transmission network (aOR 3.60, 95% CI 1.81-7.19; p<0.001). CONCLUSIONS: The high ceftriaxone-resistance level in Tianjin is mainly driven by sustained transmission of penA-60.001-harbouring strains. Ceftriaxone-resistant strains demonstrate an epidemiological transmission advantage within the studied population.