Evaluation of in vitro activity of ceftolozane-tazobactam in combination with other classes of antibacterial agents against Enterobacterales and Pseudomonas aeruginosa—the EM200 study

Ceftolozane-tazobactam is a cephalosporin/β-lactamase inhibitor combination developed for use against some β-lactam- and multidrug-resistant Gram-negative organisms. This study aimed to evaluate the in vitro activity of ceftolozane–tazobactam against clinical bacterial isolates at the University Hospital of Marrakech. This is a descriptive and analytical prospective study. A total of 143 Enterobacterales and 48 Pseudomonas aeruginosa isolates were collected from January 2018 to December 2018 from patients with respiratory, urinary and intra-abdominal infections. The identification was made by Phoenix automated system (BioMérieux). MIC50/90 were tested by broth microdilution for ceftolozane-tazobactam, and other drugs using dried panels. Antimicrobial susceptibility results were interpreted according to CLSI guidelines. Ceftolozane-tazobactam inhibited 98% of Escherichia coli (MIC(50/90); 0.25/0.5 μg/mL). The susceptibility rate of Klebsiella pneumoniae to ceftolozane-tazobactam was 68.8% (MIC(50/90), 0.5/>32 μg/mL); other Enterobacterales have shown susceptibility rates of 80.4% (MIC(50/90); 0.5/8 μg/mL). In carbapenemase-producing K. pneumoniae, the bla(OXA-48) mutation was found in two isolates. Susceptibility of P. aeruginosa to ceftolozane-tazobactam was 91.7% (MIC(50/90), 0.5/>32 μg/mL). In non-carbapenemase-producing P. aeruginosa, AmpC mutations were found in all isolates. Ceftolozane-tazobactam was satisfactorily active against a wide range of tested isolates and offers clinicians a potential therapeutic option even against resistant strains in patients with intra-abdominal infections, urinary tract infections and nosocomial pneumonia.