Definition of cefixime-decreased susceptibility

Historically, defining decreased susceptibility or resistance of N. gonorrhoeae to cefixime has been challenging due to the scarcity of treatment failure cases.³⁷ The most up-to-date recommendations of antimicrobial minimum inhibitory concentration (MIC) breakpoints by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) and the Clinical and Laboratory Standards Institute (CLSI) in the USA are as follows:

EUCAST: susceptible ≤0.125 μg mL⁻¹; resistant >0.125 μg mL⁻¹.⁴⁴

CLSI: susceptible ≤ 0.25 μg mL⁻¹; intermediate: not applicable; resistant: not applicable.⁴⁵

However, those recommendations might be too liberal when we compare those breakpoints to reported cases of clinical treatment failure. Allen et al. reported that the frequency of treatment failure with cefixime for gonococcal infections with an MIC ≥0.12 μg mL⁻¹ was 25%, compared with 1.9% among those with an MIC <0.12 μg mL⁻¹.²⁴ For this review, we have described the molecular characteristics of all N. gonorrhoeae strains reported, to date, with a MIC ≥0.12 μg mL⁻¹ as having a ‘decreased susceptibility’ to cefixime.