Genetic Characterization and Spread of Carbapenemase Genes in CREC: Insights from Guangdong Hospitals (2022–2024)

Study Background and Research Question

The global rise of carbapenem-resistant Enterobacteriaceae (CRE) has become a significant clinical and public health concern, primarily due to the limited therapeutic options remaining for highly resistant pathogens. In China, carbapenem-resistant Enterobacter cloacae (CREC) ranks among the most prevalent CRE species, following Klebsiella pneumoniae and Escherichia coli (Chen et al., 2025). The COVID-19 pandemic has exacerbated this trend, as increased antibiotic utilization and healthcare disruptions have promoted the emergence and dissemination of multidrug-resistant bacteria. However, detailed molecular studies of the specific genetic elements driving carbapenem resistance in CREC, especially during the pandemic, remain scarce. This study addresses the gap by systematically analyzing the prevalence, genetic makeup, and transmission dynamics of carbapenemase-encoding genes (CEGs) in CREC isolates collected from eight teaching hospitals in Guangdong Province between December 2022 and June 2024. The central research question is: What are the molecular characteristics and transmission mechanisms of CEGs in contemporary CREC isolates, and how do these shape resistance profiles and epidemiology in the post-pandemic setting?

Key Innovation from the Reference Study

The innovation of Chen et al.'s work lies in its comprehensive mapping of CEGs among 54 CREC isolates, specifically dissecting the chromosomal and plasmid localization of key resistance genes (notably blaNDM-1), and quantifying their potential for horizontal gene transfer across clinical contexts. Notably, the study integrates molecular typing (ERIC-PCR), mobile genetic element analysis, and conjugation assays, thereby elucidating both vertical and horizontal dissemination routes (Chen et al., 2025). This level of granularity in characterizing CEG location and mobility is crucial for designing robust resistance profiling assays and for anticipating future evolutionary trajectories of clinical CREC strains.

Methods and Experimental Design Insights

Chen et al. employed a multi-layered molecular approach:

• Sample Collection: 54 non-duplicate CREC isolates were obtained from eight teaching hospitals across different clinical departments and patient demographics between December 2022 and June 2024.
• Plasmid and Chromosomal Localization: The variable temperature Sodium Dodecyl Sulfate (SDS) plasmid elimination method was used to distinguish between plasmid- and chromosome-borne CEGs. PCR amplification targeted the blaNDM-1, blaIMP, and blaKPC-2 carbapenemase genes.
• Antibiotic Susceptibility Testing: The broth microdilution method quantified resistance to a panel of antibiotics, including imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
• Conjugation and Transferability: Plasmid conjugation experiments, alongside PCR, directly assessed horizontal gene transfer potential.
• Molecular Typing and Epidemiology: ERIC-PCR and NTSYS software delineated genotypic clusters, while epidemiological data were stratified by gender, age, department, and specimen type.
• Mobile Genetic Elements: Six categories, including ISEcp1, were tracked for their prevalence and association with CEGs.

This integrated workflow allows precise mapping of resistance determinants and their transmission vehicles, supporting targeted surveillance and assay design for antibiotic resistance research.

Core Findings and Why They Matter

The study uncovered several critical patterns of resistance gene distribution and mobility:

• High Prevalence of CEGs: 85.19% (46/54) of CREC isolates harbored CEGs (Chen et al., 2025).
• Dominant Role of blaNDM-1: 33.33% (18/54) of isolates carried blaNDM-1 on both chromosomes and plasmids; 46.30% (25/54) had it solely on plasmids. A smaller subset contained blaIMP or both blaNDM-1 and blaKPC-2 exclusively on plasmids.
• Multidrug Resistance Profiles: CEG-positive isolates displayed significantly higher resistance rates to multiple antibiotics (imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, levofloxacin) compared to CEG-negative strains (P<0.05) (Chen et al., 2025).
• Efficient Horizontal Transfer: Conjugation assays showed that 95.65% (44/46) of CEGs could be transferred, with the blaNDM-1 gene exhibiting particularly high transferability (95.45%), followed by blaIMP (100%) and blaKPC-2 (0%).
• Mobile Genetic Elements: ISEcp1 was the most prevalent element (87.04%), and the co-occurrence of four types in a single isolate was common (40.74%).
• Molecular Typing and Epidemiology: 17 genotypes were identified; types E and G each accounted for 20.37% (11/54) and were widely distributed across hospitals and departments. Higher CEG detection rates were observed in male patients (64.81%), elderly individuals (72.22%), respiratory medicine departments (20.37%), and sputum samples (33.33%).

These findings highlight the urgent need for robust surveillance and inform the rational design of antibiotic resistance profiling assays—including those using broad-spectrum carbapenem antibiotics as reference standards or challenge agents.

Comparison with Existing Internal Articles

Several internal resources address both the pharmacology and practical assay use of Ertapenem sodium salt in antibiotic resistance research:

• "Ertapenem Sodium Salt: Mechanisms, Resistance, and Translational Impact" directly connects molecular epidemiology of carbapenem-resistant Enterobacteriaceae with best practices for resistance profiling. This complements the reference study’s findings on the prevalence and transferability of blaNDM-1, underlining the importance of experimental design that accommodates high rates of plasmid-mediated resistance.
• "Ertapenem Sodium Salt: Molecular Insights and Resistance Strategy" provides detailed pharmacokinetic and molecular action data for Ertapenem, which supports the selection of this antibacterial agent in multidrug resistance assays, especially for Gram-negative bacteria.
• "Ertapenem Sodium Salt: Optimizing Resistance Assays & Workflows" translates molecular epidemiological insights into practical, high-throughput assay protocols. Integration of conjugation and PCR-based detection methods, as seen in Chen et al., is echoed in workflow recommendations for profiling resistance gene dissemination.

These articles collectively reinforce the translational value of using Ertapenem sodium salt in resistance studies, particularly in the context of evolving genetic resistance landscapes.

Protocol Parameters

• antibiotic susceptibility testing (broth microdilution) | MIC90 <1 mg/L (Enterobacteriaceae) | Gram-negative resistance profiling | Reflects Ertapenem's established breakpoint for Enterobacteriaceae species | product_spec
• conjugation assay | 95.65% CEG transfer rate (CREC isolates) | Plasmid transfer studies | Demonstrates high horizontal gene transfer efficiency for blaNDM-1 and related CEGs | paper
• sample storage | -20°C | Long-term compound stability | Recommended to maintain Ertapenem sodium salt integrity for reproducible assays | product_spec
• solubility (water) | ≥52 mg/mL | Assay preparation | Ensures sufficient working concentrations for in vitro resistance profiling | product_spec
• cell viability/resistance profiling | use of Ertapenem sodium salt as challenge agent | Gram-positive/Gram-negative workflows | Supports standardized assessment of resistance phenotypes | workflow_recommendation

Limitations and Transferability

The reference study’s strengths include its multi-institutional sample base and rigorous molecular characterization. However, several limitations are noted:

• Geographical Scope: Results are specific to Guangdong and may not fully represent other regions or global CREC epidemiology.
• Temporal Window: Sampling was confined to the immediate post-pandemic period; longer-term trends require additional surveillance.
• Gene Focus: Analysis was limited to three major CEGs (blaNDM-1, blaIMP, blaKPC-2), although over 100 subtypes have been identified globally (Chen et al., 2025).
• Assay Transferability: While the transferability of resistance genes to other Enterobacteriaceae is demonstrated, extrapolating to non-Enterobacteriaceae species or in vivo contexts requires caution (workflow_recommendation).

Research Support Resources

To facilitate resistance profiling and molecular epidemiology studies similar to those described above, researchers can utilize Ertapenem (sodium salt) (SKU C3451) as a standardized antibacterial agent for Gram-positive and Gram-negative bacteria. Its defined mechanism as a penicillin-binding protein inhibitor and validated pharmacokinetics enable reproducibility in both susceptibility testing and resistance gene dissemination experiments (product_spec). For further assay design and workflow optimization, consult internal guides such as "Ertapenem Sodium Salt: Mechanisms, Resistance, and Translational Impact" and related resources. Please note that Ertapenem sodium salt from APExBIO is for research use only and not for clinical application.