Determination of Fusidic Acid Susceptibility of Multidrug-resistant Gonococcal Isolates from China

The currently recommended gonococcal therapies are rapidly losing efficacy and; therefore, novel options for treatment are urgently required to ensure future treatment remains available. Here we investigated the susceptibility of 379 contemporary clinical Neisseria gonorrhoeae isolates from China for susceptibility to fusidic acid. These isolates include numerous multidrug-resistant strains with resistance or reduced susceptibility against ceftriaxone and/or azithromycin, antimicrobials that are currently recommended as a first-line dual therapy. Although official susceptibility breakpoints have not been established, all gonococcal isolates appeared to be susceptible to fusidic acid, with the majority of isolates displaying a minimal inhibitory concentration (MIC) of 0.25 or 0.5 mg/L. Overall, the MIC 90 was 0.5 mg/L, with a MIC range of 0.08–2 mg/L. Importantly, no correlation between fusidic acid susceptibility and susceptibility to ceftriaxone or azithromycin was observed. Further analysis of gonococcal survival curves indicated that fusidic acid was only mildly bactericidal at the highest tested concentrations (4× MIC). In conclusion, fusidic acid displayed consistent antimicrobial activity against N. gonorrhoeae and, given the absence of cross-resistance with ceftriaxone and azithromycin, might be interesting for further evaluation of single or dual antimicrobial therapies in combination with ceftriaxone or azithromycin.