Carbapenemase-producing organisms remain a growing threat, driving the need for rapid and accurate detection
The increased prevalence of carbapenemase-producing organisms (CPOs) pose a significant concern for the management of multidrug‑resistant infections. With limited treatment options and high transmission potential, these organisms stand out as particularly difficult pathogens to control, as well as a growing threat for healthcare systems.
Usually consisting of gram-negative bacteria such as Klebsiella pneumoniae, Escherichia coli, and Enterobacter cloacae, along with non-fermenters such as Pseudomonas and Acinetobacter, CPOs produce enzymes that break down carbapenems, a last-resort class of antibiotics. The genes behind this resistance (KPC, NDM, VIM, IMP, OXA-48–like) are often located on mobile plasmids, allowing resistance to spread across species and facilities.1
According to the CDC, the end of 2025 brought a 3.8% increase of CPOs across the US.1 While this number may seem small, in the world of antimicrobial resistance, even a slight uptick matters. These bacteria are experts at spreading, and every new case adds pressure on hospitals and infection control teams.
However, despite strong efforts from antimicrobial stewardship programs, some regions still face gaps in detection and containment. That means it’s time to double down on strategies that work, especially those that help us identify these organisms quickly and accurately.
Phenotypic vs. molecular detection
Detection strategies fall into two complementary categories: phenotypic and molecular. Together, they deliver both functional confirmation and mechanism clarity. Please refer to the chart below comparing phenotypic vs. molecular detection:
| Feature | Phenotypic Methods | Molecular Methods |
| Examples | Modified Hodge Test (MHT), inhibitor-based methods such as the mCIM/eCIM (modified carbapenem inactivation method with or without EDTA), and rapid biochemical tests like the Carba NP or commercial kits such as NG-Test CARBA 5 | PCR, multiplex PCR, real time PCR |
| What it Detects | Enzyme activity (functional expression) | Presence of resistance genes including specific carbapenemase genes |
| Speed | >3 hours | Fast (~1-3 hours) |
| Accuracy | Good, but can miss low-level/variable expression | Remarkably high for gene detection |
| Interpretation | Confirms enzyme activity | Confirms genetic potential (may not always be expressed) |
| Use Case | Clinical resistance assessment | Epidemiology, outbreak tracking, confirm resistance mechanism |
Phenotypic assays such as Carba NP and mCIM detect carbapenem hydrolysis/activity directly, whereas molecular assays rapidly pinpoint which gene is present (KPC vs. NDM vs. OXA48–like), enabling targeted therapy and containment.2
However, as the CDC warns of ongoing transmission risks and a rise in NDM-producing carbapenem-resistant Enterobacterales (CRE), relying solely on phenotypic screening can slow critical interventions. This stresses the critical need for molecular platforms that offer rapid, accurate, and comprehensive coverage to stay ahead of these evolving threats.
Diasorin’s LIAISON PLEX® Gram-Negative Blood Culture Assay delivers exactly that, offering:
- Multiplex PCR assay that cover broad OXA variants (including OXA-23, -24/40, 48, 58, 143 and 235), essential for selecting appropriate β‑lactam/β‑lactamase inhibitor combinations (effective for KPC producers, but not for many NDM/OXA‑48–like producers). Inclusion of SME (Serratia marcescens enzyme).
- Assists in resistance identification allowing for stronger infection prevention, rapid cohorting, and contact precautions around carriers and high-risk wards.
- Support surveillance and stewardship, delivering precise genetic-level epidemiology.
What the CDC data tells us, and where to act
The Week 52, 2025 CDC report underscores that while national cumulative totals rose 3.8%, regional differences persist. East, North, Central, Pacific, and Mountain regions carry a large share of cases, for example, hinting at local epidemiology and capacity gaps. Additionally, focusing screening, molecular capacity, and inter‑facility communication in these areas can curb spread more effectively than broad, uniform measures.1
This national increase in reported CPOs is not just a statistic, it’s an early signal that resistant mechanisms are still finding opportunities to spread, and capacity is uneven across regions. Combining robust phenotypic screening with rapid, mechanism-specific molecular testing should be the new standard of care. Platforms like LIAISON PLEX® Gram-Negative Blood Culture (BCN) Assay can help labs detect resistance faster, act earlier, and contain smarter—better protecting patients and strengthening healthcare systems against the evolving challenge of carbapenemase-mediated resistance.1,2
Download the LIAISON PLEX® Gram-Negative Antibiotic Resistance Quick Reference Guide