In-vitro activity of ceftolozane/tazobactam against Pseudomonas Aeruginosa and Enterobacterales isolates from Taiwan

Background. Ceftolozane/tazobactam (TOL/TAZ), a new antipseudomonal cephalosporin combined with a β-lactamase inhibitor, is indicated for the treatment of complicated intra-abdominal infections (requiring in combination with metronidazole), complicated urinary tract infections, and nosocomial or ventilator-associated pneumonia. Methods. Activities of TOL/TAZ and ten comparators (cefepime, cefoperazone/sulbactam, ceftazidime, ciprofloxacin, colistin, imipenem, levofloxacin, meropenem, piperacillin/tazobactam [PIP/TAZ] and tigecycline) were evaluated against isolates collected in Taiwan. The susceptibility was tested by broth microdilution methods. Results. A total of 599 isolates were collected during 2012-2015, including intra-abdomen (n = 223), respiratory tract (n = 153), urine (n = 149), skin and soft tissue (n = 55), blood (n = 11) and others (n = 8). TOL/TAZ demonstrated a good activity against Enterobacterales isolates (n = 446; 84.8% susceptibility; susceptible breakpoint, ≤ 2 μg/mL). TOL/TAZ was highly active versus Citrobacter koseri (n = 15), Klebsiella oxytoca (n = 30), Morganella morganii (n = 15), Proteus mirabilis (n = 30), and Escherichia coli (n = 125), with MIC₉₀ values of ≤ 1 μg/mL. TOL/TAZ had the best overall activity versus P. aeruginosa (94% susceptibility; MIC₉₀ = 4 μg/mL; susceptible breakpoint, ≤4 μg/mL), in comparison to imipenem (59% susceptibility, MIC₉₀ >8 μg/mL), meropenem (71% susceptibility, MIC₉₀ >8 μg/mL), and colistin (100% intermediate, MIC₉₀ = 2 μg/mL). The susceptibility rates of TOL/TAZ for K. pneumoniae isolates susceptible and non-susceptible to ceftazidime were 75.2% and 31.1%, respectively. Conclusions. TOL/TAZ demonstrated potent in-vitro activity against P. aeruginosa and Enterobacterales isolates in Taiwan. TOL/TAZ is a good option for treatment of infections caused by these organisms.