Transmission Dynamics of Carbapenemase Genes in Carbapenem-Resistant Enterobacter cloacae: Insights from Guangdong, China

Study Background and Research Question

The emergence and spread of carbapenem-resistant Enterobacteriaceae (CRE) represent a significant global health concern, particularly as carbapenem antibiotics are often reserved as last-line agents against multidrug-resistant infections. Among CRE, Enterobacter cloacae complex (CREC) has seen rising prevalence in clinical settings, ranking third in detection rates among CRE in China. The COVID-19 pandemic further complicated antimicrobial resistance patterns due to increased antibiotic consumption, complex patient comorbidities, and healthcare disruptions. Despite this backdrop, detailed molecular epidemiology and transmission studies of carbapenemase-encoding genes (CEGs) in CREC, especially in the context of pandemic-era dynamics, have been limited. The study by Chen et al. (2025) directly addresses this knowledge gap by systematically characterizing the genetic basis and dissemination mechanisms of carbapenem resistance in CREC isolates from eight tertiary hospitals in Guangdong, China, collected during 2022–2024.

Key Innovation from the Reference Study

The principal innovation of Chen et al. lies in their high-resolution mapping of CEG prevalence, genetic localization (plasmid versus chromosomal), and transmission dynamics within a regional network of teaching hospitals. By integrating molecular genotyping, conjugation assays, and epidemiological metadata, the study reveals the predominance of plasmid-borne bla_NDM-1 and the extraordinary efficiency of horizontal gene transfer among CREC. Unlike prior reports that focused mainly on clinical resistance rates or single-hospital settings, this multi-center approach elucidates the diversity and mobility of resistance determinants in real-world clinical populations during a period of heightened antibiotic pressure.

Methods and Experimental Design Insights

The study analyzed 54 non-duplicate CREC isolates obtained from eight teaching hospitals between December 2022 and June 2024. The key methodological steps included:

• Plasmid Elimination and PCR: Variable temperature SDS plasmid curing was used to distinguish plasmid- versus chromosomal location of resistance genes. PCR detected the presence of key CEGs: bla_NDM-1, bla_IMP, and bla_KPC-2.
• Antibiotic Susceptibility Testing: Broth microdilution quantified resistance rates to a panel of antibiotics, allowing direct correlation between genotype and phenotype.
• Conjugation Experiments: Plasmid transferability was assessed using mating assays, followed by PCR to confirm gene transfer in recipient strains.
• Mobile Genetic Element Characterization: Six types of insertion sequences were identified, notably ISEcp1, using PCR and sequencing.
• Genotyping and Epidemiological Analysis: ERIC-PCR and NTSYS clustering classified the isolates into 17 genotypes, providing insight into clonal spread versus horizontal gene transfer. Demographic and clinical data (age, gender, department, specimen type) were collected to contextualize transmission.

Core Findings and Why They Matter

Chen et al. report several critical findings with direct implications for both hospital surveillance and experimental modeling of resistance:

• High Prevalence of CEGs: 85.19% (46/54) of isolates harbored carbapenemase genes, predominantly bla_NDM-1 (detected on both chromosomes and plasmids in 18/54 isolates, and exclusively on plasmids in 25/54 isolates), with less frequent detection of bla_IMP and bla_KPC-2.
• Plasmid-Mediated Resistance: The majority of CEGs were plasmid-borne, and conjugation experiments demonstrated a 95.65% transfer success rate among CEG-positive isolates. bla_NDM-1 and bla_IMP showed near-complete transferability, confirming robust horizontal gene transfer potential.
• Multidrug Resistance: CEG-positive isolates displayed significantly higher resistance rates to carbapenems, β-lactams, aminoglycosides, and fluoroquinolones compared to CEG-negative strains (Chen et al., 2025), underscoring the clinical challenge posed by these genotypes.
• Diversity of Mobile Elements: Six types of mobile genetic elements were identified, with ISEcp1 present in 87.04% of cases and many isolates carrying multiple element types simultaneously, facilitating gene mobilization and recombination.
• Epidemiological Patterns: Higher detection frequencies were noted in male patients (64.81%), elderly individuals (72.22%), respiratory medicine wards (20.37%), and sputum samples (33.33%). Genotyping revealed both clonal spread (e.g., strains with 100% Dice similarity across hospitals) and inter-departmental transmission, highlighting the complexity of dissemination routes.

Collectively, these data illustrate that plasmid-mediated bla_NDM-1 is a dominant driver of CREC resistance in southern China, with resistance determinants readily transferable and often associated with multidrug resistance phenotypes.

Comparison with Existing Internal Articles

Several internal articles expand upon the laboratory and translational implications of these findings. For instance, "Transmission of Carbapenemase Genes in CREC: Insights from Guangdong" recapitulates the high mobility of blaNDM-1 and its relevance for modeling horizontal gene transfer in resistance studies. "Translational Strategies in the Era of Carbapenem Resistance" and "Ertapenem Sodium Salt: Translational Strategy for Resistance Research" provide in-depth mechanistic discussion of carbapenem antibiotics, including the use of Ertapenem sodium salt as a broad-spectrum agent and experimental benchmark in antibiotic resistance research. These resources contextualize the molecular findings of Chen et al. within best-practice laboratory workflows and experimental design, emphasizing the importance of precise antibacterial agent selection and molecular tracking in resistance surveillance.

Limitations and Transferability

While the multi-center approach and detailed molecular analyses enhance the study's generalizability within Guangdong, several limitations should be noted:

• Regional Scope: Findings are based on isolates from eight hospitals in a single province, and resistance dynamics may differ in other regions or healthcare systems.
• Lack of Longitudinal Data: The study focuses on a cross-sectional collection (2022–2024) rather than long-term trends.
• Unmeasured Confounders: Potential factors such as prior antimicrobial exposure or detailed patient movement were not exhaustively analyzed.
• Transfer Experiments: While conjugation rates were high in laboratory conditions, in vivo transfer dynamics and fitness costs require further investigation.

Nevertheless, the protocol structure and molecular workflow provide a robust template for resistance gene surveillance and laboratory modeling in other settings.

Protocol Parameters

• Isolate collection: Non-duplicate clinical isolates; confirm CREC phenotype using standard susceptibility criteria.
• Plasmid elimination: SDS-based curing at variable temperatures; confirm loss of plasmid by PCR and phenotype re-testing.
• Antibiotic susceptibility: Broth microdilution; include carbapenems, cephalosporins, aminoglycosides, and quinolones.
• Conjugation assays: Mating at 37°C (overnight); select for transconjugants on antibiotic-supplemented media.
• Molecular typing: ERIC-PCR and NTSYS for cluster analysis; mobile element identification by targeted PCR/sequencing.
• Epidemiological metadata: Record patient demographics, ward, and specimen type for transmission mapping.

Research Support Resources

To facilitate laboratory modeling of carbapenem resistance and validate susceptibility results, researchers can employ Ertapenem (sodium salt) (SKU C3451), a validated antibacterial agent for Gram-positive and Gram-negative bacteria. Its defined pharmacokinetics and stability profile make it suitable for resistance profiling and gene transfer experiments, in line with the protocols described above. For additional guidance on resistance workflows and experimental design, resources from APExBIO and the internal articles linked above offer further methodological detail.