# Activity of ceftolozane/tazobactam and imipenem/relebactam against clinical isolates of Enterobacterales and Pseudomonas aeruginosa collected in Greece and Italy—SMART 2017–2021

## TL;DR

This study assesses the effectiveness of two antibiotic combinations against bacterial infections in Greece and Italy, finding they work well against many strains.

## Contribution

The study provides new data on the efficacy of ceftolozane/tazobactam and imipenem/relebactam against clinical isolates in southern Europe.

## Key findings

- Ceftolozane/tazobactam inhibited 85–87% of Enterobacterales and 94–96% of ESBL-positive isolates.
- Imipenem/relebactam inhibited 95–98% of non-CRE NME isolates and 98–99% of KPC-positive isolates.
- Both antibiotics inhibited 84% of P. aeruginosa isolates from Greece and 91–92% from Italy.

## Abstract

The current study evaluated the in vitro activities of ceftolozane/tazobactam (C/T), imipenem/relebactam (IMI/REL), and comparators against recent (2017–2021) clinical isolates of gram-negative bacilli from two countries in southern Europe.

Nine clinical laboratories (two in Greece; seven in Italy) each collected up to 250 consecutive gram-negative isolates per year from lower respiratory tract, intraabdominal, urinary tract, and bloodstream infection samples. MICs were determined by the CLSI broth microdilution method and interpreted using 2022 EUCAST breakpoints. β-lactamase genes were identified in select β-lactam-nonsusceptible isolate subsets.

C/T inhibited the growth of 85–87% of Enterobacterales and 94–96% of ESBL-positive non-CRE NME (non-Morganellaceae Enterobacterales) isolates from both countries. IMI/REL inhibited 95–98% of NME, 100% of ESBL-positive non-CRE NME, and 98–99% of KPC-positive NME isolates from both countries. Country-specific differences in percent susceptible values for C/T, IMI/REL, meropenem, piperacillin/tazobactam, levofloxacin, and amikacin were more pronounced for Pseudomonas aeruginosa than Enterobacterales. C/T and IMI/REL both inhibited 84% of P. aeruginosa isolates from Greece and 91–92% of isolates from Italy. MBL rates were estimated as 4% of Enterobacterales and 10% of P. aeruginosa isolates from Greece compared to 1% of Enterobacterales and 3% of P. aeruginosa isolates from Italy. KPC rates among Enterobacterales isolates were similar in both countries (7–8%). OXA-48-like enzymes were only identified in Enterobacterales isolates from Italy (1%) while GES carbapenemase genes were only identified in P. aeruginosa isolates from Italy (2%).

We conclude that C/T and IMI/REL may provide viable treatment options for many patients from Greece and Italy.