Transmission Dynamics of Carbapenemase-Encoding Genes in Carbapenem-Resistant Enterobacter cloacae: Insights from Guangdong Hospitals (2022–2024)

Study Background and Research Question

Carbapenem-resistant Enterobacteriaceae (CRE) present a mounting global health threat, with Enterobacter cloacae (CREC) contributing significantly to hospital-acquired infections in China. The COVID-19 pandemic has exacerbated this threat by increasing antibiotic use and disrupting healthcare workflows, potentially accelerating the emergence and spread of multidrug-resistant organisms. While carbapenemase-encoding genes (CEGs) are known drivers of resistance, their detailed genomic context, prevalence, and transmission dynamics in CREC—especially during the pandemic—have remained underexplored (source: Chen et al., 2025). This study sought to: (1) quantify and map the distribution of CEGs in CREC isolates from multiple hospitals; (2) determine the genetic vehicles (chromosome vs. plasmid) responsible for their dissemination; (3) assess the success of horizontal gene transfer; and (4) correlate genetic patterns with epidemiological features.

Key Innovation from the Reference Study

The innovation of this work lies in its high-resolution, multicenter surveillance of CEGs in CREC. By integrating molecular genetics (plasmid elimination, PCR, ERIC-PCR), phenotypic resistance profiling, and epidemiological analysis, the study provides a comprehensive view of not only the genetic determinants of resistance, but also their mobility and transmission networks. Notably, the researchers distinguished between plasmid- and chromosome-borne CEGs, systematically quantified their transferability, and mapped the spread across hospital wards and patient demographics (source: Chen et al., 2025).

Methods and Experimental Design Insights

A total of 54 non-duplicate CREC isolates were collected from eight tertiary teaching hospitals in Guangdong Province from December 2022 to June 2024. Key methodological elements included:

• Plasmid Curing and PCR: Variable temperature SDS treatment facilitated the elimination of plasmids, allowing subsequent PCR to localize CEGs (chromosomal vs. plasmid).
• Resistance Profiling: Broth microdilution determined susceptibility to a panel of antibiotics relevant to clinical management.
• Conjugation Assays: Plasmid transfer efficiency was evaluated by mating experiments, followed by PCR confirmation of transconjugants.
• Mobile Genetic Element Identification: Six types of mobile elements, including ISEcp1, were characterized to understand gene mobility.
• Genotyping: ERIC-PCR and NTSYS clustering categorized strains into genotypes, facilitating epidemiological correlation.

Protocol Parameters

• assay | variable temperature SDS plasmid elimination | sample size: 54 isolates | enables distinction between plasmid- and chromosome-borne CEGs | source: Chen et al., 2025
• antibiotic susceptibility testing | broth microdilution method | panel: imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, levofloxacin | robust for multidrug resistance profiling | source: Chen et al., 2025
• conjugation assay | filter mating, PCR confirmation | n=46 CEG-positive isolates | quantifies horizontal transfer success rates | source: Chen et al., 2025
• plasmid selection assay | chloramphenicol 25–170 μg/mL (workflow recommendation) | supports stringent or relaxed plasmid selection | aligns with resistance marker selection and molecular characterization | workflow_recommendation

Core Findings and Why They Matter

Prevalence and Genetic Context:

• 85.19% (46/54) of CREC isolates carried at least one carbapenemase-encoding gene (source: Chen et al., 2025).
• The dominant gene, blaNDM−1, was found on both chromosomes and plasmids in 33.33% (18/54) and exclusively on plasmids in 46.30% (25/54) of isolates (source: Chen et al., 2025).
• Other CEGs included blaIMP (3.70%) and co-occurring blaNDM−1 + blaKPC−2 (1.85%), all on plasmids (source: Chen et al., 2025).

Transmission and Mobility:

• Conjugation experiments demonstrated a 95.65% (44/46) success rate for horizontal transfer of CEGs, indicating high mobility (source: Chen et al., 2025).
• blaNDM−1 transfer succeeded in 95.45% (42/44), blaIMP in 100% (2/2), while blaKPC−2 did not transfer independently (0/1) (source: Chen et al., 2025).
• Six mobile genetic element types were detected; ISEcp1 was most prevalent (87.04%), and 40.74% of isolates harbored four mobile elements simultaneously (source: Chen et al., 2025).

Resistance Profiles:

• CEG-positive strains showed significantly higher resistance rates to imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin compared to CEG-negative strains (P < 0.05) (source: Chen et al., 2025).

Epidemiological Correlation:

• Higher CEG detection rates were observed in male patients (64.81%), elderly individuals (72.22%), respiratory medicine units (20.37%), and sputum specimens (33.33%) (source: Chen et al., 2025).
• Genotyping (ERIC-PCR) revealed 17 CREC genotypes; type E and type G were most prevalent (20.37% each), indicating intra- and inter-hospital dissemination (source: Chen et al., 2025).

These findings have major implications for infection control and molecular surveillance, emphasizing the need for targeted monitoring and containment strategies.

Comparison with Existing Internal Articles

Recent internal reviews, such as "Chloramphenicol in Plasmid Selection: Protocols & Innovations", provide workflow-focused guidance on using chloramphenicol as a bacterial protein synthesis inhibitor in molecular biology. This aligns with the reference study's use of plasmid elimination and selection techniques to dissect resistance mechanisms, although the internal article emphasizes troubleshooting and selectivity optimization over clinical epidemiology. Similarly, "Chloramphenicol in Translational Research: Mechanistic Pr..." contextualizes chloramphenicol as a research tool for dissecting protein synthesis inhibition and studying multidrug resistance, paralleling the reference paper's focus on gene mobility and resistance profiles. Unlike the clinical surveillance of Chen et al., these articles focus on experimental reproducibility and reagent purity for molecular workflows.

Limitations and Transferability

The study's strengths include multicenter sampling, comprehensive genotyping, and robust molecular techniques. However, several limitations warrant consideration:

• Geographical Scope: All samples were drawn from Guangdong Province, limiting direct generalizability to other regions or healthcare settings (source: Chen et al., 2025).
• Temporal Range: The surveillance period (2022–2024) captures pandemic-driven dynamics, which may not reflect pre- or post-pandemic trends.
• Functional Analysis: The study maps gene presence and transfer, but does not address in vivo pathogenicity or treatment outcomes.

Transferability to other settings depends on local epidemiology and healthcare practices. Nevertheless, the workflow—plasmid elimination, PCR, and conjugation assays—can be adapted for resistance surveillance worldwide (workflow_recommendation).

Research Support Resources

For researchers aiming to replicate or extend molecular analyses of resistance gene mobility, high-purity reagents are essential. Chloramphenicol (2,2-dichloro-N-[(1R,2R)-1,3-dihydroxy-1-(4-nitrophenyl)propan-2-yl]acetamide, SKU: A2512) from APExBIO is validated for use in plasmid selection assays and as a bacterial protein synthesis inhibitor in molecular biology workflows (source: product_spec). For further evidence-driven guidance on integrating chloramphenicol into resistance gene studies, see "Chloramphenicol in Plasmid Selection: Protocols & Innovations".