Dissecting Carbapenemase Gene Transmission in CREC: Insights from Guangdong Hospitals (2022–2024)

Study Background and Research Question

The global rise of carbapenem-resistant Enterobacteriaceae, particularly Enterobacter cloacae (CREC), represents a formidable challenge for healthcare systems. During the COVID-19 pandemic, increased empirical antibiotic use and healthcare disruptions may have accelerated the emergence and spread of multidrug-resistant organisms. Despite CREC ranking as the third most prevalent carbapenem-resistant Enterobacteriaceae in China, the genetic drivers, transmission dynamics, and clinical epidemiology of carbapenemase-encoding genes (CEGs) in CREC during this period have remained under-characterized. The study by Chen et al. (2025) addresses this gap by systematically analyzing 54 CREC isolates from eight teaching hospitals in Guangdong Province, China, collected between December 2022 and June 2024.

Key Innovation from the Reference Study

The innovation of this work lies in its comprehensive, high-resolution mapping of CEG prevalence, genetic context, and transmissibility in a real-world clinical setting during the COVID-19 era. Unlike prior studies, Chen et al. combined advanced molecular genotyping with conjugation assays and epidemiological profiling, uncovering not only the dominant resistance genes but also their genetic vehicles—chromosomes versus plasmids—and their capacity for horizontal and vertical transfer. The study reveals that plasmid-mediated blaNDM-1 is the most prevalent mechanism, and it rigorously quantifies the conjugation efficiency of these resistance determinants, providing actionable data for resistance modeling.

Methods and Experimental Design Insights

Fifty-four non-duplicate CREC strains were isolated from clinical specimens across eight tertiary hospitals. The isolates underwent a suite of molecular and microbiological analyses:

• Plasmid Elimination and PCR: Variable temperature sodium dodecyl sulfate (SDS) plasmid curing was paired with targeted PCR to distinguish chromosomal versus plasmid localization of CEGs.
• Broth Microdilution Susceptibility Testing: This method established the resistance phenotypes and compared minimum inhibitory concentrations (MICs) across CEG-positive and -negative groups.
• Plasmid Conjugation Assays: Mating experiments quantified the efficiency of CEG transfer to recipient strains, directly measuring the horizontal gene transfer potential.
• Mobile Genetic Element Typing: PCR identified the presence and combinations of insertion sequences and transposons, mapping the genetic architecture facilitating gene mobility.
• ERIC-PCR Genotyping and Cluster Analysis: Enterobacterial repetitive intergenic consensus (ERIC)-PCR and NTSYS cluster software resolved clonal relationships and the diversity of CREC genotypes across clinical settings.

Core Findings and Why They Matter

The study's findings have several key implications for molecular epidemiology and resistance research:

• High Prevalence of CEGs: 85.19% of CREC isolates harbored carbapenemase-encoding genes, predominantly the blaNDM-1 gene, with 33.33% carrying it on both chromosomes and plasmids, and 46.30% exclusively on plasmids. A minority exhibited blaIMP or co-harbored blaKPC-2.
• Efficient Horizontal Transfer: Plasmid conjugation experiments demonstrated a 95.65% success rate for CEG transfer, with blaNDM-1 and blaIMP being highly transferable, highlighting the threat of rapid dissemination in hospital environments.
• Multidrug Resistance Phenotype: CEG-positive strains showed significantly higher resistance to imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin (P<0.05), underlining the clinical challenge posed by these isolates (Chen et al., 2025).
• Genetic Vehicles and Epidemiology: Six types of mobile genetic elements were observed, with ISEcp1 present in 87.04% of isolates. A notable 40.74% carried four types of mobile elements simultaneously, facilitating complex gene transfer mechanisms. Genotypic analysis revealed 17 distinct clusters, with types E and G prevailing across different departments and hospitals.
• Clinical and Demographic Trends: CEG detection was highest among male and elderly patients, in respiratory medicine, and in sputum samples, suggesting targeted surveillance priorities.

These results confirm and extend previous reports that multidrug resistance in CREC is mediated primarily by plasmid-borne carbapenemase genes, with a particular emphasis on blaNDM-1. The high rate of horizontal gene transfer documented here underscores the urgency of monitoring plasmid-mediated resistance in hospital settings.

Comparison with Existing Internal Articles

The present study builds upon earlier work covered in internal reviews. For example, the article "Transmission Dynamics of Carbapenemase Genes in CREC in Guangdong" aligns closely in its focus on resistance surveillance and experimental modeling, both emphasizing the central role of CEGs in shaping multidrug resistance profiles. The molecular epidemiology and conjugation efficiency data from Chen et al. add resolution to findings previously summarized in "Transmission of Carbapenemase Genes in CREC: Insights from Guangdong", with the new study providing quantitative transfer rates and detailed genotypic breakdowns. Furthermore, insights from "Ertapenem Sodium Salt: Mechanism, Activity, and Resistance Insights" contextualize the clinical impact of these resistance mechanisms, particularly in the framework of evaluating antibacterial agents for Gram-positive and Gram-negative bacteria.

Protocol Parameters

• Sample collection: Non-duplicate CREC isolates from multiple departments; prioritize respiratory medicine and elderly patient populations to increase detection rates.
• Plasmid curing: SDS (variable temperature) method for selective elimination of plasmid DNA prior to PCR typing.
• CEG detection: Multiplex PCR targeting blaNDM-1, blaIMP, and blaKPC-2. Confirm localization on chromosome versus plasmid by post-curing PCR.
• Antibiotic susceptibility testing: Broth microdilution in accordance with CLSI guidelines to determine resistance phenotype spectrum.
• Conjugation assays: Filter mating with E. coli recipient; select for transconjugants on carbapenem-containing media to quantify transfer efficiency.
• Mobile element typing: PCR screen for insertion sequences (e.g., ISEcp1) and transposons; categorize by combinatorial presence for epidemiological mapping.
• Genotyping: Perform ERIC-PCR and NTSYS cluster analysis to resolve transmission networks.

Limitations and Transferability

The study's main limitations stem from its regional focus and sample size, restricting generalizability to other geographic regions or non-tertiary care settings. While the findings robustly define the landscape of carbapenemase gene dissemination in Guangdong hospitals, transferability to outpatient or community settings requires further validation. The dynamic clinical context of the COVID-19 pandemic may also influence detection rates and resistance patterns, potentially limiting extrapolation to non-pandemic periods.

Outlook: Implications for Resistance Surveillance and Experimental Modeling

By quantitatively charting the prevalence, genetic context, and transferability of CEGs in CREC, Chen et al. (2025) provide a valuable resource for designing resistance surveillance protocols and laboratory models. The data highlight the necessity of monitoring plasmid-mediated blaNDM-1 and associated mobile elements, particularly in high-risk wards and patient populations. These findings directly inform the choice of reference strains, marker screening, and experimental conjugation workflows for antibiotic resistance research. Importantly, the clear link between mobile genetic elements and multidrug resistance phenotypes reinforces the need for molecular surveillance as an integral part of infection control.

Research Support Resources

To support experimental modeling and susceptibility profiling in resistance studies, researchers may employ reference compounds such as Ertapenem (sodium salt) (SKU C3451), a broad-spectrum carbapenem antibiotic with defined activity against Gram-positive and Gram-negative bacteria and well-characterized pharmacokinetics. This compound, available from APExBIO, facilitates standardized MIC determination and conjugation assay benchmarking in CREC and related Enterobacteriaceae workflows, as outlined in the reference study and supporting internal resources. Use is restricted to scientific research applications and not for diagnostic or therapeutic purposes.