Antimicrobial susceptibility of commensal Neisseria species in the Japanese population

Objectives
We aimed to, for the first time, characterize the antimicrobial susceptibilities of commensal Neisseria species in the general population in Japan. In particular, we assessed if the tetracycline minimum inhibitory concentrations (MICs) of these isolates were changing over time and, given the recent interest in doxycycline post exposure prophylaxis (PEP), if the tetracycline MICs were associated with those of the other antimicrobials.
Methods
Neisseria spp. were isolated from 1679 patients visiting dental clinics in Japan between 2018 and 2023. The MICs of tetracycline, ceftriaxone, cefixime, penicillin, azithromycin and ciprofloxacin against Neisseria spp. were determined using agar dilution. Linear regression was used to assess if there was an association between MIC and the year the isolate was obtained from, controlling for species identity.
Results
Neisseria spp. were detected in 424 of 1679 individuals sampled. Of these, 417 (98.3 %) isolates were identified as Neisseria subflava, and the remaining 7 (1.7 %) as Neisseria mucosa. The median tetracycline MIC was 0.5 mg/L (IQR 0.5–1 mg/L). The MICs of penicillin, cefixime, ceftriaxone and ciprofloxacin were lower in N. mucosa than in N. subflava. The tetracycline MICs of Neisseria spp. were positively correlated with penicillin, azithromycin and ciprofloxacin. No significant correlations were found with cefixime or ceftriaxone.
Conclusions
Our results suggest that despite the overall decline in antimicrobial use in Japan, MICs for several antimicrobials have increased over time. In particular, the MIC of tetracycline tends to be high in Japan. These results suggest the need to include surveillance of tetracycline MICs of commensal Neisseria spp. in doxycycline PEP implementation studies.