Azithromycin susceptibility of oral streptococci in Belgian men who have sex with men and the general population: a comparison of two cross-sectional surveys

Background: Excessive antimicrobial consumption may saturate the relationship between subsequent antimicrobial exposure and resistance. The ResistAZM randomised controlled trial in Belgium found that 2 g of azithromycin had no effect on the prevalence of macrolide resistance in oral streptococci. At baseline, macrolide resistance was, however, pervasive in this population of men who have sex with men with high exposure to antimicrobials.

Methods: The authors used the same sampling and laboratory protocol to assess if the streptococcal azithromycin susceptibilities in the ResistAZM study were higher than those from isolates obtained from the Belgian general population with lower consumption of antimicrobials (ComCom2023 study).

Results: Streptococcal azithromycin minimum inhibitory concentrations (MIC) were higher in the ResistAZM (median: 32 mg/L; interquartile range: 12–96 mg/L) than in the ComCom2023 study (median: 1 mg/L; (interquartile range: 0.5–12 mg/L; P<0.00001). The azithromycin MICs of S. mitis/oralis, S. parasanguinis, and S. sanguinis were all significantly higher in the ResistAZM study.

Interpretation: The authors found that the streptococcal macrolide MIC distribution of the ResistAZM participants was significantly higher than that of the Belgian general population in 2023. These findings are compatible with the saturation hypothesis and strengthen the argument that more discriminatory methods are needed to evaluate the effects of antimicrobials on antimicrobial resistance in populations exposed to high levels of antimicrobials. The authors’ findings add support to stewardship initiatives that aim to reduce antimicrobial consumption in this population.