Deciphering Carbapenemase Gene Dissemination in CREC: Evidence from Eight Hospitals in Guangdong, China

Study Background and Research Question

Carbapenem-resistant Enterobacter cloacae (CREC) has emerged as a critical threat within the broader context of antimicrobial resistance, particularly in China, where detection rates have steadily risen across clinical settings. The COVID-19 pandemic has exacerbated this trend, with increased antibiotic use and healthcare disruptions facilitating the spread of multidrug-resistant organisms. While carbapenemase-encoding genes (CEGs) have been identified as the principal mediators of carbapenem resistance in Enterobacteriaceae, the specific genetic landscape and transmission dynamics within CREC populations remain insufficiently characterized, especially during pandemic conditions (Chen et al., 2025).

Key Innovation from the Reference Study

The study by Chen and colleagues provides a high-resolution, multi-institutional analysis of CEGs in 54 CREC isolates collected from eight teaching hospitals in Guangdong Province between December 2022 and June 2024. The primary innovation lies in the combined use of molecular epidemiology, plasmid conjugation assays, and genotyping to reconstruct the structure, prevalence, and transferability of key resistance genes—most notably blaNDM−1, blaIMP, and blaKPC−2—across diverse clinical environments (paper).

Methods and Experimental Design Insights

The investigators applied a suite of molecular and microbiological techniques:

• Variable temperature SDS plasmid elimination and PCR analysis to determine the location and prevalence of carbapenemase genes.
• Broth microdilution for antimicrobial susceptibility profiling, including fluoroquinolone antibiotics such as ciprofloxacin, imipenem, and others.
• Plasmid conjugation assays to assess horizontal gene transfer efficiency.
• ERIC-PCR and NTSYS clustering for genotypic diversity and epidemiological tracing.

This integrated approach enabled the differentiation of chromosomal versus plasmid-associated resistance determinants and the quantification of their transfer potential.

Protocol Parameters

• assay | variable temperature SDS plasmid elimination | 42–45°C, 0.1–0.2% SDS | CEG localization | Standard method for distinguishing plasmid versus chromosomal carriage | paper
• assay | broth microdilution | CLSI/EUCAST breakpoints | Antimicrobial susceptibility | Quantitative assessment of resistance levels | paper
• assay | plasmid conjugation | liquid mating, 18–24 h | Horizontal gene transfer | Evaluates transmissibility of CEGs | paper
• assay | ERIC-PCR | 94°C-65°C-72°C cycling | Genotyping | Differentiates strain clusters and transmission | paper

Core Findings and Why They Matter

The study’s principal findings elucidate both the genetic and epidemiological complexity of CREC resistance (paper):

• High prevalence of CEGs: 85.19% of isolates harbored carbapenemase genes, with blaNDM−1 the most common (on both chromosomes and plasmids in 33.33% of cases; exclusively on plasmids in 46.30%).
• Plasmid-mediated transfer dominates: Plasmid conjugation assays showed a 95.65% success rate for horizontal transfer of CEGs, underscoring the role of mobile elements in disseminating multidrug resistance.
• Multidrug resistance phenotype: CEG-positive strains exhibited significantly higher resistance rates to multiple antibiotics, including ciprofloxacin (fluoroquinolone antibiotic), imipenem, cefepime, gentamicin, ceftazidime/avibactam, and levofloxacin, when compared to CEG-negative strains (P < 0.05) (paper).
• Diverse mobile genetic elements: Six types were identified, with ISEcp1 present in 87.04% of isolates. Many strains co-harbored multiple elements, increasing recombination and transfer potential.
• Epidemiological clustering: The 54 isolates fell into 17 genotypes, with two dominant types (E and G) distributed across multiple hospitals, suggesting both intra- and inter-hospital transmission.
• Patient and specimen trends: Higher detection rates occurred in males, elderly patients, respiratory departments, and sputum samples, informing surveillance priorities.

Collectively, these data confirm that both horizontal and vertical gene transfer mechanisms are active and efficient in clinical CREC populations, facilitating rapid adaptation to antibiotic pressure—including fluoroquinolone classes such as ciprofloxacin.

Comparison with Existing Internal Articles

Recent internal literature corroborates and contextualizes these findings for the research community. For example, "Ciprofloxacin at the Frontiers of Translational Antibiotic Research" synthesizes molecular mechanisms of DNA gyrase and topoisomerase IV inhibition by ciprofloxacin, emphasizing its utility in resistance gene transmission studies. The current reference paper provides new epidemiological precision on how CREC resistance genes—often conferring cross-resistance to fluoroquinolones—are structured and mobilized in real clinical isolates, directly informing experimental design and benchmarking protocols for fluoroquinolone mechanism of action studies.

Further, "Ciprofloxacin in Antimicrobial Resistance Research Workflows" offers actionable lab guidance for dissecting DNA replication inhibition and resistance development, complementing the present study’s demonstration that CEG-positive CREC strains manifest higher fluoroquinolone resistance. These internal resources together encourage the use of well-characterized CREC isolates and high-purity fluoroquinolone antibiotics for robust resistance modeling.

Limitations and Transferability

While Chen et al. present a comprehensive dataset, several constraints merit consideration:

• Regional specificity: Isolates were collected only from teaching hospitals in Guangdong, potentially limiting generalizability to other healthcare settings or geographic regions.
• Gene scope: The study focused primarily on blaNDM−1, blaIMP, and blaKPC−2; other resistance determinants may also contribute to the observed multidrug resistance but were not exhaustively characterized.
• Temporal window: Sampling occurred during the COVID-19 pandemic, a period of abnormal healthcare dynamics, which may have influenced strain prevalence and transmission patterns.

Nevertheless, the methodological framework—integrating plasmid mapping, conjugation, and resistance profiling—offers a robust template for analogous studies in other regions and for other Enterobacteriaceae species.

Research Support Resources

For researchers intending to replicate or extend these workflows, access to high-purity, well-characterized fluoroquinolone antibiotics is essential. Ciprofloxacin (SKU A8399) from APExBIO is widely used in laboratory models to investigate DNA replication inhibition, resistance gene transmission, and antimicrobial efficacy in multidrug-resistant Gram-negative bacteria. Its well-defined mechanism as a topoisomerase inhibitor makes it suitable for experimental designs paralleling those described in this study. Researchers are advised to follow appropriate solvent and storage protocols for optimal compound stability (workflow_recommendation).