Plasmid-Mediated Carbapenemase Transmission in CREC: Insights from Guangdong Hospitals

Study Background and Research Question

Carbapenem-resistant Enterobacter cloacae (CREC) presents a critical challenge in healthcare due to its ability to evade last-resort antibiotics. The COVID-19 pandemic has further complicated antimicrobial stewardship, leading to increased antibiotic use, disrupted patient management, and a heightened risk of resistance gene propagation. Despite the recognized threat, fine-scale data on the genetic mechanisms and transmission dynamics of carbapenemase-encoding genes (CEGs) in CREC remain limited, particularly in high-prevalence regions such as Guangdong, China. The reference study aimed to elucidate the prevalence, genetic context, and horizontal transfer efficiency of CEGs among CREC isolates from eight teaching hospitals during 2022–2024 (Chen et al. 2025).

Key Innovation from the Reference Study

A major advance of this work lies in its systematic, multi-center investigation combining molecular epidemiology, plasmid profiling, and horizontal gene transfer assays. By integrating variable temperature SDS plasmid elimination, PCR, conjugation experiments, and genotyping, the authors provide a granular view of CEG prevalence (with special focus on bla_NDM-1, bla_IMP, and bla_KPC-2), their chromosomal/plasmid localization, and their mobility potential under pandemic-driven selective pressures (Chen et al. 2025).

Methods and Experimental Design Insights

Fifty-four non-redundant CREC strains were collected prospectively from December 2022 to June 2024 across eight tertiary hospitals. The experimental workflow included:

• CEG detection: Variable temperature SDS-based plasmid curing followed by targeted PCR to determine gene presence and location.
• Resistance profiling: Broth microdilution for antimicrobial susceptibility, including assessment against fluoroquinolones such as ciprofloxacin and levofloxacin.
• Gene transferability: Plasmid conjugation assays to quantify horizontal dissemination rates of individual carbapenemase genes.
• Mobile genetic elements: PCR mapping of insertion sequences and transposons to contextualize CEG mobility.
• Genotyping: ERIC-PCR and similarity analysis (NTSYS) to infer clonal relationships and intra-hospital spread.

This comprehensive design ensured robust linkage between genotypic features and phenotypic resistance, while supporting epidemiological inferences (Chen et al. 2025).

Protocol Parameters

• broth microdilution | standardized microdilution volumes (μL) | antimicrobial susceptibility testing in CREC | ensures comparability across resistance studies | paper
• PCR detection | specific primer sets per CEG | gene localization (chromosome vs plasmid) | distinguishes horizontal vs vertical gene transmission | paper
• conjugation assay | filter-mating at 37°C | horizontal transfer quantification | assesses real-world dissemination potential | paper
• antibiotic panel | includes ciprofloxacin, levofloxacin, imipenem, gentamicin, ceftazidime/avibactam, cefepime | multidrug resistance profiling | reflects clinical relevance and aligns with global resistance monitoring | paper
• workflow suggestion | use high-purity research-grade Ciprofloxacin (e.g., SKU A8399) in broth microdilution assays for consistent resistance benchmarking | antimicrobial resistance research | standardizes susceptibility testing in laboratory models | workflow_recommendation

Core Findings and Why They Matter

Key results from the study are striking:

• 85.19% (46/54) of isolates harbored one or more CEGs, with bla_NDM-1 as the dominant allele (paper).
• 33.33% (18/54) carried bla_NDM-1 on both plasmid and chromosome, while 46.30% (25/54) had it exclusively on plasmids, highlighting the risk of rapid horizontal dissemination (paper).
• Plasmid conjugation experiments demonstrated a 95.65% (44/46) transfer success for CEGs, with particularly high rates for bla_NDM-1 (95.45%) and bla_IMP (100%) (paper).
• Multidrug resistance was pronounced: CEG-positive strains showed significantly elevated resistance rates to imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin (P<0.05) (paper).
• Six classes of mobile genetic elements were found, with ISEcp1 being the most prevalent (87.04%), supporting concerns over mobilizable resistance determinants (paper).
• Genotyping revealed 17 distinct strain types; type E and G predominated (each 20.37%), and identical genotypes appeared in multiple institutions, underscoring inter-facility spread (paper).
• Demographically, CEG-positive CREC was most common in male, elderly patients, especially in respiratory departments and sputum samples (paper).

These findings illuminate the critical role of plasmids in disseminating carbapenemase genes, reinforce the need for molecular surveillance, and validate the use of multidrug resistance panels—including fluoroquinolone antibiotics such as ciprofloxacin—for laboratory modeling of clinical resistance scenarios.

Comparison with Existing Internal Articles

Several internal resources provide valuable context for researchers utilizing fluoroquinolone antibiotics in antimicrobial resistance research:

• Ciprofloxacin: Fluoroquinolone Antibiotic for Advanced Antimicrobial Resistance Research—This article reviews the mechanism of ciprofloxacin as a bacterial DNA gyrase and topoisomerase IV inhibitor, paralleling its inclusion in resistance panels in the reference study. The use of high-purity ciprofloxacin is emphasized for experimental consistency (source: internal).
• Ciprofloxacin: Precision Tools for Antimicrobial Resistance Research—Protocols and troubleshooting strategies for benchmarking resistance in Gram-negative infection models are detailed, aligning with the study's focus on multidrug resistance profiling in CREC (source: internal).
• Ciprofloxacin in Antibiotic Research: Mechanisms and Experimental Insights—Highlights the importance of fluoroquinolone mechanism-of-action studies in multidrug resistance contexts. The reference paper's demonstration of high-level ciprofloxacin resistance in CEG-positive CREC provides real-world validation for such laboratory models (source: internal).

These resources collectively support the integration of fluoroquinolone antibiotics, like ciprofloxacin, into resistance evolution and mechanism-of-action studies, echoing the reference study's methodology and clinical relevance.

Limitations and Transferability

While the study provides a robust multi-institutional snapshot, its scope is regionally confined to Guangdong and temporally limited to the COVID-19 era. The sample size, though substantial for molecular epidemiology, may not capture the full genetic diversity of CREC in other settings. Furthermore, real-world transferability of conjugation rates and resistance phenotypes would benefit from in vivo validation. Nonetheless, the high prevalence and mobility of CEGs, especially bla_NDM-1, underscore urgent needs for molecular diagnostics, infection control, and research on resistance prevention strategies (Chen et al. 2025).

Research Support Resources

For laboratories modeling multidrug resistance or benchmarking fluoroquinolone mechanism of action, researchers can utilize Ciprofloxacin (SKU A8399) from APExBIO. This high-purity, research-grade fluoroquinolone antibiotic offers reliable DNA replication inhibition and is suitable for use in broth microdilution and resistance gene transmission studies, as exemplified by the reference study and related internal protocols (workflow_recommendation).