Material and Method: One thousand one hundred thirty six clinical isolates of Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Staphylococcus aureus isolated from different Thai patients with urinary tract infections or lower respiratory tract infections in 2016 were included. The minimum inhibitory concentrations (MICs) of sitafloxacin, ciprofloxacin, levofloxacin, amoxicillin-clavulanate, ceftriaxone, ceftazidime, piperacillin-tazobactam, tigecycline, imipenem, meropenem, and colistin were determined by standard agar dilution method.

Results: The MIC50 and MIC90 values of sitafloxacin against all tested bacteria were lowest when compared with those of levofloxacin and ciprofloxacin. Sitafloxacin was more active than levofloxacin, ciprofloxacin, amoxicillin-clavulanate, ceftriaxone, and ceftazidime, but it was less active than piperacillin-tazobactam, tigecycline, imipenem, meropenem, and colistin against extended-spectrum beta-lactamase (ESBL)-producing E. coli isolates. Sitafloxacin was more active than levofloxacin, ciprofloxacin, amoxicillin-clavulanate, ceftriaxone, and ceftazidime against ESBL-producing K. pneumoniae. The activity of sitafloxacin against ESBL-producing K. pneumoniae was comparable to piperacillin-tazobactam, but it was less active than tigecycline, imipenem, meropenem, and colistin. Sitafloxacin was more active than levofloxacin, ciprofloxacin, ceftazidime, piperacillin-tazobactam, imipenem, and meropenem, but it was less active than colistin against A. baumannii isolates. The activity of sitafloxacin against P. aeruginosa isolates was comparable to levofloxacin, ciprofloxacin, ceftazidime, piperacillin-tazobactam, imipenem, and meropenem, but it was less active than colistin. The in vitro activity of sitafloxacin against methicillin-resistant S. aureus (MRSA) isolates was more than levofloxacin, but it was less than vancomycin. The activities of sitafloxacin against tested bacteria isolated from the patients in 2016 were not significantly different from those isolated in 2010.

Conclusion: Sitafloxacin remains active against the common antibiotic-resistant bacteria causing urinary tract infections and lower respiratory tract infections in Thai patients isolated in 2016, including ESBL-producing E. coli, ESBL-producing K. pneumoniae, A. baumannii, P. aeruginosa, and S. aureus, after its use in Thailand for five years.

Keywords: In vitro activity, Sitafloxacin, Fluoroquinolone