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Plasmid-Mediated Carbapenemase Gene Spread in CREC: Insights
2026-08-05
Plasmid-Mediated Carbapenemase Gene Spread in CREC: Insights from Guangdong Hospitals
Study Background and Research Question
Carbapenem-resistant Enterobacter cloacae (CREC) has rapidly emerged as a major concern within the broader context of carbapenem-resistant Enterobacteriaceae (CRE), which pose significant threats to global public health due to their capacity for extensive antimicrobial resistance. CREC now ranks third in CRE detection rates in China, with its prevalence increasing annually and across many clinical departments. The COVID-19 pandemic further complicated resistance dynamics, as increased antibiotic use and healthcare disruptions created new opportunities for the selection and transmission of multidrug-resistant organisms. However, prior to the current study, in-depth molecular characterization of carbapenemase-encoding genes (CEGs) and their transmission dynamics—particularly during the pandemic—remained limited. Chen et al. (2025) aimed to address this gap by systematically analyzing 54 CREC isolates from eight teaching hospitals in Guangdong Province, China, collected between December 2022 and June 2024 (reference study).Key Innovation from the Reference Study
The principal innovation of Chen et al.'s work lies in their comprehensive dissection of CEG localization, transferability, and epidemiological patterns within a real-world clinical context. Uniquely, the study not only evaluates the prevalence of major carbapenemase genes—including blaNDM-1, blaIMP, and blaKPC-2—but also distinguishes between chromosomal and plasmid-borne occurrences. This level of molecular resolution is crucial for understanding both vertical and especially horizontal gene transfer, which underpins the rapid dissemination of resistance traits in hospital settings. Furthermore, the research integrates genetic typing, plasmid conjugation assays, and analysis of associated mobile genetic elements to construct a detailed map of CREC resistance evolution during a period of heightened antimicrobial pressure.Methods and Experimental Design Insights
Chen et al. employed a multi-pronged methodological approach:- Isolation and Identification: Fifty-four CREC strains were collected from diverse clinical departments and specimen types across eight tertiary hospitals.
- CEG Detection and Localization: The presence of carbapenemase genes (notably blaNDM-1, blaIMP, blaKPC-2) was detected using PCR, with subsequent localization to either plasmid or chromosomal DNA via variable temperature Sodium Dodecyl Sulfate (SDS) plasmid elimination and further PCR mapping.
- Antimicrobial Susceptibility Testing: Broth microdilution was used to assess resistance profiles, comparing CEG-positive versus CEG-negative groups.
- Conjugation Experiments: Plasmid transfer efficiency was evaluated through mating assays to assess the real-world potential for horizontal gene dissemination.
- Genotyping and Mobile Element Analysis: ERIC-PCR and NTSYS clustering software categorized the strains into genotypes, while the presence of six key mobile genetic elements (insertion sequences, transposons) was determined, with ISEcp1 being the most prevalent.
Core Findings and Why They Matter
Key results from the study include:- High Prevalence of CEGs: 85.19% of isolates harbored carbapenemase genes, with blaNDM-1 being the most widespread. Notably, 33.33% of isolates carried blaNDM-1 on both plasmid and chromosome, while 46.30% had it exclusively on plasmids.
- Horizontal Gene Transfer Efficiency: Conjugation experiments demonstrated that 95.65% of CEG-positive isolates could successfully transfer resistance genes via plasmids, with a 95.45% transfer rate for blaNDM-1 and 100% for blaIMP. The inability to transfer blaKPC-2 in this cohort suggests variability in genetic context or plasmid compatibility.
- Multidrug Resistance Phenotypes: CEG-positive isolates showed significantly elevated resistance rates to major antibiotics, including imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin (reference study).
- Mobile Genetic Elements: Six types of mobile elements were identified, with ISEcp1 found in 87.04% of strains. The most prevalent pattern was the simultaneous presence of four elements, supporting the notion of complex mobilizable resistance platforms.
- Epidemiological Patterns: Higher detection rates of CEGs were observed in male patients, the elderly, respiratory medicine departments, and sputum specimens—highlighting demographic and clinical risk factors relevant for targeted surveillance.
- Genetic Diversity and Epidemiology: ERIC-PCR profiling classified the isolates into 17 genotypes, with types E and G predominant across hospitals and departments, indicating both clonal spread and diverse sources.
Comparison with Existing Internal Articles
Several recent internal reviews provide complementary context to the findings of Chen et al. (Carbapenemase Gene Transmission in CREC; Transmission Dynamics of Carbapenemase Genes in CREC, 2022–2024). These articles confirm the high prevalence of plasmid-mediated CEGs—especially blaNDM-1—and highlight the important role of horizontal gene transfer in shaping local resistance epidemiology. Notably, the internal resources emphasize the clinical risk factors (age, gender, department) and the urgent need for integrating molecular biology workflows into routine surveillance. In addition, related methodological articles (Chloramphenicol in Multidrug Resistance Research) provide practical guidance on leveraging chloramphenicol as a bacterial protein synthesis inhibitor in plasmid selection assays—a technique foundational to experimental studies of resistance gene mobility and stability. This linkage underscores the translational bridge between epidemiological surveillance and experimental molecular biology.Limitations and Transferability
Despite its strengths, the study is subject to certain limitations. The geographic focus on Guangdong limits immediate generalizability to other regions, where the local prevalence and genetic context of CEGs may differ. Sampling during the COVID-19 pandemic introduces confounders related to altered antibiotic use and healthcare practices, which may not reflect post-pandemic dynamics. Additionally, while the study characterized major carbapenemase genes, other resistance determinants or less common mobile elements may have been missed. Nevertheless, the methodological framework—combining PCR, conjugation, and genotyping—offers a robust template for similar studies elsewhere. The high transferability of findings lies in the demonstration of efficient plasmid-mediated dissemination, which is relevant to diverse hospital and clinical settings globally.Protocol Parameters
- Plasmid elimination (SDS method): Variable temperature protocol was used to distinguish plasmid-borne versus chromosomal CEGs; ensure careful control of incubation to prevent unwanted loss of target plasmids.
- CEG detection (PCR): Use gene-specific primers for blaNDM-1, blaIMP, and blaKPC-2, with validated controls for both chromosomal and plasmid templates.
- Conjugation assays: Employ recipient strains lacking carbapenemase genes, with selection on media containing carbapenem antibiotics to monitor transfer efficiency.
- ERIC-PCR genotyping: Standardize DNA input and cycling conditions for reproducible cluster analysis using NTSYS software.
- Antimicrobial susceptibility testing: Broth microdilution with interpretation according to current CLSI or EUCAST guidelines.
- Chloramphenicol for plasmid selection assays: Use at 25 μg/ml for stringent and 170 μg/ml for relaxed plasmids, as advised in the product information, ensuring compatibility with the host strain's resistance profile.