Characterizing Carbapenemase Gene Transmission in CREC: Insights from a Multicenter Study in Guangdong

Study Background and Research Question

Carbapenem-resistant Enterobacter cloacae (CREC) has emerged as a critical challenge in clinical microbiology due to its capacity for multidrug resistance and its increasing prevalence in healthcare settings. The COVID-19 pandemic has further complicated this landscape, as heightened antibiotic use and altered hospital practices have potentially accelerated resistance evolution and dissemination. Chen et al. (2025) aimed to fill crucial knowledge gaps by systematically analyzing the prevalence, genetic context, and transmission dynamics of carbapenemase-encoding genes (CEGs) in CREC isolates collected from eight teaching hospitals in Guangdong, China, between December 2022 and June 2024 (reference study).

Key Innovation from the Reference Study

This study distinguishes itself by integrating advanced molecular epidemiology with clinical surveillance across multiple institutions. Notably, it provides the first detailed mapping of both the chromosomal and plasmid localization of CEGs—especially blaNDM-1, blaIMP, and blaKPC-2—in a representative cohort during the intense healthcare pressures of the COVID-19 period. The authors systematically tracked the mobility of resistance genes, quantifying both their prevalence and their conjugative transfer capacity. This dual focus on genetic context and transmissibility yields actionable insights for molecular surveillance and infection control.

Methods and Experimental Design Insights

The research team employed a combination of microbiological and molecular approaches. Fifty-four non-duplicate CREC isolates were collected from eight teaching hospitals. Plasmid elimination was achieved using the variable temperature sodium dodecyl sulfate (SDS) method, followed by PCR amplification to detect carbapenemase genes. The distribution of blaNDM-1, blaIMP, and blaKPC-2 was further resolved to plasmid versus chromosomal loci. Broth microdilution assays established antibiotic resistance profiles. Plasmid conjugation experiments evaluated horizontal transfer rates of CEGs. Mobile genetic elements were characterized, and ERIC-PCR genotyping, combined with NTSYS software, was used to define clonal relationships among strains.

Protocol Parameters

• Plasmid elimination: Variable temperature SDS treatment as per Chen et al. (2025); details in supplementary data.
• Carbapenemase gene detection: PCR using gene-specific primers for blaNDM-1, blaIMP, blaKPC-2.
• Antibiotic susceptibility: Broth microdilution with imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
• Gene transfer assay: Plasmid conjugation with selection for transconjugants on antibiotic-containing medium.
• Genotyping: ERIC-PCR and cluster analysis using NTSYS for genetic relatedness.

Core Findings and Why They Matter

The analysis revealed that 85.19% of the CREC isolates harbored CEGs. Notably, the blaNDM-1 gene was the most prevalent, detected in 33.33% of isolates on both chromosomes and plasmids, and in 46.30% exclusively on plasmids. A smaller percentage carried blaIMP or a combination of blaNDM-1 and blaKPC-2. The study found that isolates positive for CEGs exhibited significantly higher resistance rates to multiple antibiotics compared to CEG-negative strains, highlighting the multidrug-resistant nature of these pathogens.

Plasmid conjugation experiments showed a high horizontal transfer rate of CEGs (95.65%), with particularly efficient transfer of blaNDM-1 and blaIMP, but not blaKPC-2. Six types of mobile genetic elements were identified, with ISEcp1 being the most frequent, suggesting a robust genetic infrastructure for resistance gene mobility. The ERIC-PCR genotyping resolved 17 genetic types, with types E and G dominating across institutions, indicating both clonal expansion and inter-hospital transmission. Epidemiologically, CEG-positive CREC was most frequently detected in male and elderly patients, particularly in respiratory medicine departments and sputum samples.

These findings collectively underscore the rapid and efficient spread of high-risk resistance determinants within and between healthcare facilities during the pandemic, reinforcing the imperative for targeted molecular surveillance and infection control strategies.

Comparison with Existing Internal Articles

The results of Chen et al. (2025) are concordant with previous analyses, such as the review in "Transmission Dynamics of Carbapenemase Genes in CREC in China", which also identified the predominance and mobility of plasmid-borne blaNDM-1 in CREC from Guangdong hospitals. Similarly, "Plasmid-Borne Carbapenemase Genes in Enterobacter cloacae: Dynamics and Resistance Patterns" emphasized the capacity for both horizontal and vertical gene transfer, aligning with the high conjugation rates and molecular diversity reported in the reference study. These internal articles reinforce the importance of detailed molecular epidemiology for designing intervention strategies and highlight the relevance of plasmid selection assays and molecular tools for dissecting resistance transmission.

For researchers interested in the methodological aspects of resistance gene selection and plasmid dynamics, the internal article "Chloramphenicol: Precision Antibiotic for Plasmid Selection Assays" provides complementary insights, especially regarding the use of bacterial protein synthesis inhibitors in molecular workflows.

Limitations and Transferability

While the study provides a robust cross-sectional snapshot of CEG dynamics in Guangdong during the pandemic, it is limited by its geographic and temporal scope. The findings may not fully capture resistance trends in other regions or post-pandemic contexts. The reliance on culture-based methods and PCR limits the detection of novel or cryptic resistance genes. Moreover, only a subset of mobile genetic elements and CEGs were investigated, and the study does not directly address clinical outcomes or intervention efficacy. Nevertheless, the high transferability and prevalence of blaNDM-1, especially on plasmids, highlight patterns likely to be relevant in other high-transmission healthcare environments.

Research Support Resources

For laboratories investigating plasmid-driven resistance mechanisms or conducting plasmid selection assays, Chloramphenicol (2,2-dichloro-N-[(1R,2R)-1,3-dihydroxy-1-(4-nitrophenyl)propan-2-yl]acetamide, SKU A2512) is widely used as a potent bacterial protein synthesis inhibitor. Its mode of action—binding to the 50S ribosomal subunit and inhibiting peptidyl transferase—enables stringent selection for plasmid maintenance in molecular biology workflows, as described in the product information. Researchers may find chloramphenicol-based selection particularly relevant for tracking plasmid-borne genes such as those characterized in the reference study. For optimal results, follow best practices for solution preparation and storage as outlined by APExBIO. This compound is intended for research use only and not for clinical or diagnostic applications.