Ceftolozane/tazobactam activity against drug-resistant Enterobacteriaceae and Pseudomonas aeruginosa causing urinary tract and intraabdominal infections in Europe: report from an antimicrobial surveillance programme (2012-15)

Objectives: To evaluate the in vitro activity of ceftolozane/tazobactam and comparators tested against European isolates of Enterobacteriaceae and Pseudomonas aeruginosa from hospitalized patients with urinary tract infection or intraabdominal infections. Methods: A total of 6553 Gram-negative organisms (603 P. aeruginosa and 5950 Enterobacteriaceae) were consecutively collected from 41 hospitals located in 17 European countries plus Israel and Turkey. The organisms were tested for susceptibility by broth microdilution methods and the results interpreted according to EUCAST and CLSI breakpoint criteria. Results: Ceftolozane/tazobactam [MIC50/90 0.25/1 mg/L; 93.5%/91.3% susceptible (S) (CLSI/EUCAST criteria)] and meropenem [MIC50/90 <= 0.06/<= 0.06mg/L; 98.1%/98.3% S (CLSI/EUCAST)] were the most active compounds tested against Enterobacteriaceae. Among the Enterobacteriaceae isolates, 1.9% were carbapenem resistant (CRE), 15.2% exhibited an ESBL non-CRE phenotype, 14.6% were MDR, 2.2% were XDR and <0.1% were pan-drug resistant (PDR). Whereas ceftolozane/tazobactam showed activity against ESBL non-CRE phenotype isolates (MIC50/90 0.5/8 mg/L), it lacked useful activity against strains with a CRE (MIC50/90 >32/> 32 mg/L; 3.6% S) or PDR (MIC50 >32 mg/L; 0.0% S) phenotype. Ceftolozane/tazobactam was the most potent (MIC50/90 0.5/4 mg/L) beta-lactam agent tested against P. aeruginosa isolates, inhibiting 91.7% at an MIC of <= 4 mg/L. P. aeruginosa exhibited high rates of resistance to cefepime (20.6%), ceftazidime (23.1%), meropenem (9.0%) and piperacillin/tazobactam (26.9%) (EUCAST criteria). Among these four P. aeruginosa resistant phenotypes, 61.3%-70.4% were susceptible to ceftolozane/tazobactam. Conclusions: Ceftolozane/tazobactam was the most active beta-lactam agent tested against P. aeruginosa and demonstrated higher in vitro activity than currently available cephalosporins and piperacillin/tazobactam when tested against Enterobacteriaceae.