Carbapenem resistance and susceptibility to Ceftazidima/avibactam and Ceftolozane/tazobactam in Pseudomonas aeruginosa and Enterobacterales in a reference laboratory in Lima, Peru: A cross-sectional study

Carbapenem resistance in Pseudomonas aeruginosa and Enterobacterales is a growing threat, with intrinsic and acquired resistance mechanisms resulting in the need for new therapeutic options. In Peru, data on resistance patterns and the effectiveness of new antibiotic combinations are limited A descriptive, cross-sectional, retrospective study was conducted on P. aeruginosa and Enterobacterales clinical isolates collected from 2019 to 2024 at a reference laboratory in Lima, Peru, originating from various public and private healthcare centers. Bacterial identification was performed using VITEK MS MALDI-TOF, and antimicrobial susceptibility testing via VITEK 2 and/or Kirby-Bauer disk diffusion. Carbapenemase production was detected using colorimetric, immunochromatographic, and molecular methods, including the FilmArray® BCID panel for bloodstream infections. Microbiological and epidemiological variables were analyzed with Poisson regression models. A total of 173,308 isolates were analyzed, with E. coli (74%) and K. pneumoniae (10.6%) being most prevalent. Most samples (92%) were urinary. Meropenem resistance in P. aeruginosa reached 33% overall and 60% in respiratory specimens. K. pneumoniae showed 3.4% carbapenem resistance. Among carbapenem-resistant isolates, 43.7% were carbapenemase producers. Carbapenemase production was highest in carbapenem-resistant K. pneumoniae (93.1%), E. coli (87.3%), and P. mirabilis (77.3%), but only 32.7% in P. aeruginosa . Among carbapenemase-producing Enterobacterales, metallo-β-lactamases predominated, with bla-NDM detected in 69.6% of K. pneumoniae and bla-OXA-48-like in 100% of E. coli . Ceftazidime/avibactam (CZA) and ceftolozane/tazobactam (C/T) were highly active (>89%) against non-carbapenemase-producing P. aeruginosa , but <1% effective against producers. Resistance was more common in northern, eastern, and southern Lima. P. aeruginosa exhibited high carbapenem resistance, largely driven by non-carbapenemase mechanisms, supporting the role of C/T for treatment of non-carbapenemase-producing carbapenem-resistant P. aeruginosa. Among Enterobacterales, carbapenemase production was frequent in carbapenem-resistant isolates, with metallo-β-lactamases predominating. The limited activity of CZA against MBL producers underscores the urgent need for novel β-lactam/β-lactamase inhibitor combinations to address MBL-producing Enterobacterales.