In vitro antimicrobial activity of nitroxoline against uropathogens isolated from China.

Background and objectives: The antimicrobial nitroxoline is used in treating uncomplicated urinary tract infections (UTIs) in some European countries. In vitro antimicrobial data on uropathogens from China are lacking. To investigate the activity of nitroxoline in vitro against uropathogens isolated from Chinese patients.

Methods: MICs of nitroxoline were determined using broth microdilution of 229 bacterial isolates of 10 species including Acinetobacter baumannii derived from urinary sample. The EUCAST susceptibility breakpoint for Escherichia coli (16 mg/L) was applied for all isolates. The MBC for A. baumannii (n = 34) was determined, with the MBC defined as the nitroxoline concentration at which a 99.9% reduction in the initial inoculum was observed. Time-kill curves of the two isolates of A. baumannii were tested over a 24 h period.

Results: Except for Pseudomonas aeruginosa, most isolates were susceptible to nitroxoline. The MIC50/90 values of nitroxoline for E. coli, Klebsiella pneumoniae and Proteus mirabilis were 4/8, 8/32 and 8/16 mg/L, respectively. Among the Gram-negative isolates, nitroxoline demonstrated a better inhibitory effect against A. baumannii with an MIC50/90 value of 2/2 mg/L. The MBC of A. baumannii was equal to the MIC or one dilution higher. The time-kill curves of A. baumannii displayed concentration-dependent killing.

Conclusions: Nitroxoline showed excellent in vitro activity against uropathogens isolated from China and may be a good option for uncomplicated UTIs caused by A. baumannii, which are more challenging and have few clinical options. Further in vivo efficacy studies are needed.