Objective  To investigate the role of a novel rpsE gene mutation in mediating high-level spectinomycin resistance in Neisseria gonorrhoeae and to evaluate its effect on the biological fitness of the bacteria.

Methods Spectinomycin-containing medium was used to screen for Neisseria gonorrhoeae strains with spontaneous mutations that conferred spectinomycin resistance. Minimum inhibitory concentrations (MIC) were determined, and the rpsE gene was sequenced. Changes in the growth rates of spectinomycin-resistant strain were assessed using the drop plate method and growth curves. Additionally, in vitro competition experiments were conducted with spectinomycin at different concentrations to assess changes in the biological fitness of the spectinomycin-resistant strain.

Results A Neisseria gonorrhoeae strain with high-level spectinomycin resistance mediated by a novel rpsE gene mutation (88_90delGTT) was successfully identified and designated NG-SPT^R. Compare with the wild-type strain, the NG-SPT^R exhibited reduced growth rate (optical density OD comparison, P < 0.05). In addition, in vitro competition experiments showed a competitive index (CI) < 1 in gonococcal base liquid (GCBL) without or with low-concentration spectinomycin (≤ 16 μg/mL). In the GCBL with 32 μg/mL spectinomycin, the CI value gradually increased from < 1 before 18 h to > 1 after 18 h. The mutant strain showed CI > 1 in GCBL with spectinomycin concentrations ≥ 64 μg/mL.

Conclusion  The rpsE gene mutation (88_90delGTT) mediates high-level spectinomycin resistance in Neisseria gonorrhoeae, and imposes a fitness cost on the bacteria. The biological fitness of the mutant strain is influenced by the concentration of spectinomycin.