Purpose: STI clinic clients frequently receive antibiotics to treat sexually transmitted infections (STIs). This may select for antibiotic resistance among their commensal microbiota. We hypothesized that non-pathogenic oropharyngeal neisseriae of men who have sex with men (MSM) are less susceptible to antibiotics than those of the general population. Methods & Materials: In 2019-2020 we enrolled 96 participants at our STI clinic in Antwerp, Belgium: one group of 32 clinic employees representing the “general population” (group I) and two groups of 32 MSM (group II and III). Group I and II did not use antibiotics in the previous 6 months, whereas group III did. EswabsTM were taken from their oropharynx, plated onto modified Thayer-Martin and blood agar and incubated in 5% carbon dioxide at 36.5°C for 24 hours. Neisseria-like colonies were identified to the species level with MALDI-TOF. Minimum inhibitory concentrations (MICs) of azithromycin, ciprofloxacin and ceftriaxone were determined by E-tests®. Species diversity and MICs were compared between groups using non-parametric tests. Results: Participants’ median age was 35 (IQR 35 – 47.5). We isolated 172 non-pathogenic Neisseria colonies, representing seven different species. Data did not differ significantly between MSM of group II and III, so their data were combined. Prevalence of non-pathogenic neisseriae was 100.0% among employees and 51.6% among MSM (p<0.0001). MICs of azithromycin and ciprofloxacin were significantly higher among MSM compared with employees (azithromycin: 8.0 mg/L [IQR 3.5–268.0 mg/L] versus 3.0 mg/L, [IQR 2.0–3.6 mg/L] p<0.001; ciprofloxacin: 0.250 mg/L [IQR 0.032–0.381 mg/L] versus 0.024 mg/L [IQR 0.016–0.101 mg/L], p<0.001). MIC of ceftriaxone did not differ significantly between MSM (0.056 [IQR 0.032–0.086 mg/L]) and employees (0.043 mg/L [IQR 0.028–0.056 mg/L], p=0.25). Conclusion: MICs of oropharyngeal neisseriae from members of the general Belgian population were remarkably high, and those from STI clinic clients were ...