Evaluation of alternative antibiotics for susceptibility of gonococcal isolates from China.

Abstract

Efficacy of the currently last available first-line treatment ceftriaxone monotherapy or ceftriaxone/azithromycin dual therapy is waning, while novel antimicrobials for gonococcal infections are not going to be available in the near future. Therefore, the aim of this study was to screen alternative clinically approved antimicrobials for in vitro activity against N. gonorrhoeae. The susceptibility levels of 504 clinical isolates from Zhejiang Province, China, to ertapenem, tigecycline, gentamicin, fosfomycin, gemifloxacin, doxycycline and rifampicin was investigated by agar dilution method. Presence of resistance determinants was identified by PCR and sequencing. The MIC90 was 0.06 mg/L for ertapenem, 0.25 mg/L for tigecycline, 16 mg/L for doxycycline, 4 mg/L for gemifloxacin, 16 mg/L for gentamicin, 32 mg/L for fosfomycin and 128 mg/L for rifampicin. All strains appeared to be susceptible to tigecycline (MIC ≤0.5 mg/L), while a poor correlation between tigecycline and tetracycline susceptibility was observed, indicating that tetracycline resistance determinants have little impact on tigecycline susceptibility. For ertapenem, 30 isolates showed an MIC >0.125 mg/L, but the correlation between ertapenem and ceftriaxone susceptibility was low and only 2 strains showed an MIC >0.125 mg/L for both antibiotics. Therefore, it appeared that most ceftriaxone-resistant isolates were still susceptible to ertapenem. In conclusion, tigecycline and ertapenem showed good activity against N. gonorrhoeae and limited cross-resistance with previously used antibiotics. Therefore, they might be interesting candidates for further evaluation of their suitability as alternative anti-gonococcal therapies.