An improved algorithm to screen for carbapenemase production in Pseudomonas aeruginosa - antimicrobial susceptibility testing-based screening algorithm

Sep 30, 2026

Objective: address the difficulty of screening for carbapenemase-producing, carbapenem-resistant Pseudomonas aeruginosa by developing an improved algorithm using routine AST results. Methods: compare antibiograms from 100 reference isolates with diverse phenotypes and genotypes, then apply the derived rule to 1482 clinical isolates. Carbapenemase PCR and a modified carbapenem inactivation method are used for confirmation. Results: the algorithm uses meropenem, ceftazidime, and tobramycin and shows 100% sensitivity and 96.6% specificity. Conclusions: confirmatory testing can be substantially reduced while maintaining sensitivity across varying carbapenemase epidemiology.

LanguageEnglish

CategoryHealthcare

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Pages5

Reading Time13 min

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Materials and methods

JAC Antimicrob Resist [https://doi.org/10.1093/jacamr/dlaf249](https://doi.org/10.1093/jacamr/dlaf249) JACAntimicrobial Resistance An improved algorithm to screen for carbapenemase production in Pseudomonas aeruginosa Justin A. Ellem1,2*, Mitchell J. Brown1, Indy Sandaradura 1, Brian P. McSharry2,3 and Thiru Vanniasinkam2 1Centre for Infectious Diseases and Microbiology Laboratory Services, NSW Health Pathology-ICPMR, Westmead Hospital, Sydney, Australia; 2School of Dentistry and Medical Sciences, Faculty of Science and Health, Charles Sturt University, Wagga Wagga, Australia; 3Gulbali Institute, Charles Sturt University, Wagga Wagga, Australia *Corresponding author. E-mail: [justin.ellem@health.nsw.gov.au](justin.ellem@health.nsw.gov.au) Received 1 July 2025; accepted 28 November 2025 Objectives: One of the biggest challenges for healthcare providers is the difficulty with screening for carbapenemase-producing, carbapenem-resistant Pseudomonas aeruginosa (CP-CRPa; P. aeruginosa), given the variety of mechanisms that can mediate carbapenem resistance in P. aeruginosa. We sought to develop an improved algorithm to screen for carbapenemase activity in P. aeruginosa using routine antimicrobial susceptibility testing readily available in most clinical microbiology laboratories. Methods: Antibiograms of a reference set of P. aeruginosa (n = 100) with diverse phenotypic and genotypic profiles were compared to determine which antibiotics optimally screen for and differentiate CP-CRPa from CRPa and non-CRPa. The developed algorithm was then applied to 1482 clinical P. aeruginosa isolates. Carbapenemase PCR and the modified carbapenem inactivation method were performed on all meropenem-resistant P. aeruginosa isolates. Results: The CP-CRPa screening algorithm developed here uses meropenem, ceftazidime and tobramycin. Carbapenem resistance was identified in 85 (5.7%) isolates, of which 26 (1.8%) were confirmed as CP-CRPa. blaGES (57.7%) was the predominant carbapenemase detected, whilst blaNDM, blaVIM, blaIMP and blaKPC carbapenemases were also detected. The CP-CRPa screening algorithm was 100% sensitive (CI95% 84.0%–100%) and 96.6% specific (CI95% 87.3%–99.4%) . Conclusions: We present an antimicrobial susceptibility testing-based screening algorithm that uses meropenem, ceftazidime, and tobramycin to screen for CP-CRPa. When appropriate screening criteria are utilized, confirmatory testing can be significantly reduced, resulting in substantial time and resource savings, without compromising sensitivity, particularly in settings with varying carbapenemase epidemiology. Introduction Pseudomonas aeruginosa is a leading cause of healthcareassociated infections, including serious respiratory and bloodstream infections.1 A major characteristic of P. aeruginosa is its intrinsic resistance to many antibiotics and its ability to acquire new resistance mechanisms.2 Carbapenem resistance in P. aeruginosa is of significant clinical concern, mediated by several key mechanisms that work individually or in combination to reduce antibiotic efficacy.3 Often combined, hyperproduction of chromosomal AmpC cephalosporinases and inactivation or repression of the OprD outer membrane porin protein are the major mechanisms causing resistance to essentially all anti-pseudomonal β-lactams, including carbapenems.4 A second mechanism is the overexpression of the resistance-nodulation-division efflux pumps, particularly MexABOprM. The MexAB-OprM efflux pump expels most β-lactam antibiotics, including carbapenems, from the cell using a proton gradient to the extracellular environment.2,5,6 Acquisition of carbapenemase genes is the third key mechanism, and although the frequency of carbapenemase production in P. aeruginosa is still relatively low in many geographical regions, the prevalence of carbapenemase production appears to be increasing.7 Screening for carbapenemase-producing, carbapenemresistant P. aeruginosa (CP-CRP

FAQs

What problem does the study address in healthcare microbiology?

Screening for carbapenemase-producing, carbapenem-resistant Pseudomonas aeruginosa is challenging because carbapenem resistance can arise through multiple mechanisms and EUCAST provides no specific guidance for this species.

Which routine AST agents are included in the developed screening algorithm?

The algorithm uses meropenem, ceftazidime, and tobramycin based on routine susceptibility testing results.

How accurate is the screening algorithm for detecting CP-CRPa?

It demonstrates 100% sensitivity (CI95% 84.0%–100%) and 96.6% specificity (CI95% 87.3%–99.4%) in the reported analysis.

Sep 30, 2026

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