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    • Carbapenemase Gene Dynamics in CREC: Plasmid Transfer and Re

    2026-06-12

    Characterizing Carbapenemase Gene Dynamics in Carbapenem-Resistant Enterobacter cloacae

    Study Background and Research Question

    Carbapenem-resistant Enterobacteriaceae (CRE) present a major clinical threat due to limited treatment options and rapid global dissemination. Among these, carbapenem-resistant Enterobacter cloacae (CREC) has shown a marked increase in prevalence, now ranking third in CRE detection rates in China. The emergence and spread of carbapenemase-encoding genes (CEGs), particularly during the COVID-19 pandemic when antibiotic use and healthcare disruptions intensified, have raised concerns regarding resistance evolution and infection control. The reference study (Chen et al., 2025) investigates the molecular epidemiology, localization, and transmission dynamics of CEGs in CREC isolates from eight teaching hospitals in Guangdong province, aiming to clarify the mechanisms driving multidrug resistance and spread in clinical settings.

    Key Innovation from the Reference Study

    A central innovation of the study is its systematic analysis of both the chromosomal and plasmid localization of CEGs in a clinically relevant collection of CREC isolates sampled during the pandemic. By coupling plasmid elimination, PCR-based gene detection, and conjugation assays, the authors dissect the specific mechanisms facilitating horizontal and vertical gene transfer. Notably, the study distinguishes between chromosomal and plasmid-borne blaNDM-1, blaIMP, and blaKPC-2 genes, providing quantitative insights into their prevalence and transferability. This multi-level approach reveals the dominant role of plasmid-mediated transmission and the co-occurrence of multiple mobile genetic elements underpinning resistance spread (Chen et al., 2025).

    Methods and Experimental Design Insights

    The authors collected 54 non-duplicate CREC isolates between December 2022 and June 2024 across eight tertiary hospitals. The variable temperature sodium dodecyl sulfate (SDS) plasmid elimination method, combined with PCR, was used to determine the presence and localization of carbapenemase genes. The study further utilized broth microdilution to assess antimicrobial susceptibility, and plasmid conjugation experiments to evaluate the horizontal transfer potential of CEGs. Mobile genetic elements were characterized, and genotyping was performed using ERIC-PCR and NTSYS analysis to define strain diversity and track epidemiological relationships.

    Protocol Parameters

    • Plasmid elimination: Variable temperature SDS method; used to distinguish chromosomal vs. plasmid localization of resistance genes.
    • Gene detection: PCR assays targeting blaNDM-1, blaIMP, and blaKPC-2.
    • Antimicrobial susceptibility: Broth microdilution for imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
    • Plasmid conjugation: Filter mating assays to test transferability of CEGs to recipient strains.
    • Genotyping: ERIC-PCR and cluster analysis via NTSYS software.

    Core Findings and Why They Matter

    The study found that 85.19% of CREC isolates carried CEGs. The blaNDM-1 gene was the most prevalent, present in 33.33% of isolates on both chromosomes and plasmids, and in 46.3% exclusively on plasmids. Additional isolates harbored blaIMP or both blaNDM-1 and blaKPC-2 on plasmids. Importantly, the resistance rate to key antibiotics was significantly higher in CEG-positive strains, confirming the functional impact of these genes on multidrug resistance (Chen et al., 2025). Plasmid conjugation experiments demonstrated a high success rate (95.65%) for CEG transfer, especially for blaNDM-1 and blaIMP, highlighting the efficiency of horizontal gene dissemination. Six types of mobile genetic elements were identified, with ISEcp1 being the most prevalent. The simultaneous presence of up to four mobile elements in single strains suggests remarkable genetic plasticity and the potential for rapid adaptation. Genotypic analysis categorized the isolates into 17 genotypes, with two dominant types spreading across multiple hospitals and departments. Epidemiological data indicated higher CEG detection rates among male and elderly patients, within respiratory medicine, and in sputum samples—information that may guide infection control priorities.

    Comparison with Existing Internal Articles

    Several internal resources contextualize and reinforce the findings of Chen et al. For example, the article on Carbapenemase Genes in CREC: Plasmid Dynamics and Resistance Patterns corroborates the high prevalence of plasmid-mediated resistance and the dominance of blaNDM-1, strengthening the argument that mobile elements drive multidrug resistance in clinical Enterobacter strains. Additionally, Transmission Dynamics of Carbapenemase Genes in CREC During COVID-19 offers parallel epidemiological insights, emphasizing the pandemic's role in accelerating resistance spread. These internal articles collectively highlight the necessity of robust plasmid selection models and precise molecular tools for dissecting resistance mechanisms. For laboratory strategies, resources such as Chloramphenicol in Plasmid Selection: Protocols & Troubleshooting translate these resistance findings into practical workflows, including the use of chloramphenicol for stringent plasmid selection and resistance gene transfer studies—an essential step for modeling horizontal gene transfer in vitro.

    Limitations and Transferability

    The study's hospital-based sampling, while extensive, is limited to Guangdong province and a defined period during the COVID-19 pandemic. This may influence both the spectrum of detected genotypes and the observed prevalence of resistance determinants. The focus on transferable CEGs (e.g., blaNDM-1, blaIMP, blaKPC-2) provides a high-resolution view of horizontal gene transfer, but additional resistance mechanisms (such as efflux or porin loss) are not addressed. Furthermore, while conjugation assays confirm gene mobility, in vivo transfer dynamics and clinical impact require further study. Nonetheless, the protocols and insights presented are transferable to other Enterobacteriaceae surveillance studies and can inform laboratory modeling of resistance gene spread, especially in the context of increased antimicrobial pressure and healthcare system strain.

    Research Support Resources

    For laboratories aiming to model plasmid-mediated resistance or optimize plasmid selection assays, Chloramphenicol (SKU A2512) is a widely used bacterial protein synthesis inhibitor. Its well-characterized mechanism—binding to the 50S ribosomal subunit and inhibiting peptidyl transferase—makes it suitable for selection of resistant clones and for studies on horizontal gene transfer. APExBIO offers high-purity chloramphenicol validated for molecular biology workflows, supporting robust experimental reproducibility in resistance research. For detailed protocols and troubleshooting tips specific to plasmid selection or resistance gene transfer, researchers may refer to the previously cited internal resources for scenario-driven guidance.