Comparative in vitro activity of sitafloxacin against bacteremic isolates of carbapenem resistant Acinetobacter baumannii complex

Background: The emergence of carbapenem-resistant Acinetobacter baumannii (CRAB) complex has posed a great challenge to clinicians worldwide. Sitafloxacin has been shown to have in vitro activity against pathogens resistant to other fluoroquinolones. However, data comparing the anti-CRAB activity of sitafloxacin with that of other antimicrobial agents are limited. Methods: Genospecies were identified by 16S-23S ribosomal RNA intergenic spacer sequencing. Minimum inhibitory concentrations (MICs) were determined by an agar dilution method. Isolates with sitafloxacin MICs <= 2 mg/L were provisionally considered as susceptible to sitafloxacin. The MIC breakpoint for tigecycline susceptibility was 2 mg/L. Results: A total of 167 CRAB complex blood isolates (146 A. baumannii, 7 Acinetobacter pittii, and 14 Acinetobacter nosocomialis) were collected from January 2009 to December 2011. Around 90% of the A. baumannii isolates were resistant to amikacin, cefepime, ceftazidime, piperacillin/tazobactam, ampicillin/sulbactam, ciprofloxacin, and levofloxacin. By contrast, the rate of resistance to colistin, sitafloxacin, and tigecycline was relatively low (0%, 41.1%, and 65.1%, respectively). The MIC50 and MIC90 of ciprofloxacin, levofloxacin, and sitafloxacin were 128 mg/L and >128 mg/L; 16 mg/L and 64 mg/L; 2 mg/L and 8 mg/L, respectively. Compared with ciprofloxacin and levofloxacin, sitafloxacin had a significantly lower MIC (p < 0.001), and the rate of resistance to sitafloxacin was significantly lower than that to ciprofloxacin (97.9% vs. 41.1%, p < 0.001), levofloxacin (97.3% vs. 41.1%, p < 0.001), and tigecycline (p < 0.001). Conclusion: Sitafloxacin has acceptable in vitro activity against CRAB, even against isolates resistant to other fluoroquinolones. Sitafloxacin may be considered an alternative drug of choice in treating CRAB related infections. Copyright (C) 2014, Taiwan Society of Microbiology. Published by Elsevier Taiwan LLC. All rights reserved.