Carbapenemase Gene Dynamics in Carbapenem-Resistant Enterobacter cloacae: New Insights from Guangdong Hospitals

Study Background and Research Question

Antimicrobial resistance (AMR) in gram-negative bacteria is a growing public health crisis, with carbapenem-resistant Enterobacter cloacae (CREC) emerging as a particularly challenging pathogen. CREC ranks third among carbapenem-resistant Enterobacteriaceae (CRE) in China, following Klebsiella pneumoniae and Escherichia coli (Chen et al., 2025). The COVID-19 pandemic—with its increased antibiotic usage, healthcare disruptions, and complex patient profiles—further complicated AMR epidemiology and accelerated the emergence and spread of multidrug-resistant organisms. However, until recently, there has been a lack of detailed epidemiological and molecular data on carbapenemase-encoding gene (CEG) carriage and transmission dynamics in CREC during and after the pandemic period.

Key Innovation from the Reference Study

The study by Chen et al. (2025) provides a comprehensive molecular epidemiological analysis of CEGs in 54 CREC isolates collected from eight major teaching hospitals in Guangdong Province, China, between December 2022 and June 2024. The research uniquely addresses both the chromosomal and plasmid localization of CEGs, their horizontal transfer potential, and the genotypic diversity of CREC in a post-pandemic clinical landscape (Chen et al., 2025).

Methods and Experimental Design Insights

The researchers employed a robust combination of molecular and microbiological techniques:

• Sample Collection: Fifty-four non-duplicate CREC strains were collected across multiple departments in eight hospitals.
• Plasmid Elimination: The variable temperature Sodium Dodecyl Sulfate (SDS) plasmid curing method allowed the differentiation of chromosomal vs. plasmid-borne CEGs.
• PCR and ERIC-PCR: Polymerase chain reaction (PCR) was used to detect carbapenemase genes, and enterobacterial repetitive intergenic consensus (ERIC)-PCR enabled genotyping and clonal relationship analysis.
• Broth Microdilution: Minimum inhibitory concentrations (MICs) for several antibiotics were determined, allowing for precise correlation between genotype and resistance phenotype.
• Conjugation Assays: Plasmid transferability was assessed using conjugation experiments, directly measuring the dissemination potential of CEGs.
• Mobile Genetic Element Analysis: The team identified six types of mobile genetic elements (MGEs), critical for understanding resistance gene mobility.

Key protocol parameters and applicability are summarized below.

Protocol Parameters

• Assay: Plasmid elimination | 42–45°C SDS exposure for 24–48 h | Differentiation of chromosomal vs. plasmid genes | Validates gene localization for transmission studies | paper
• Assay: PCR for CEG detection | Standard primer sets, 30–35 cycles | Identification of blaNDM-1, blaIMP, blaKPC-2 | Enables resistance gene surveillance | paper
• Assay: Broth microdilution | 0.25–128 µg/mL antibiotic range | MIC determination for multidrug panel | Correlates genotype with resistance phenotype | paper
• Assay: Conjugation | Overnight filter-mating, 37°C | Plasmid transferability assessment | Quantifies horizontal gene transfer potential | paper
• Assay: ERIC-PCR | Standard ERIC primer, 25 cycles | Clonal diversity and outbreak tracking | Delineates epidemiological relationships | paper
• Assay: Amikacin-based resistance profiling | ≥5.86 mg/mL in water (suggested stock) | Resistance mechanism elucidation, especially for aminoglycoside-modifying enzyme studies | Facilitates functional testing alongside other antibiotics | workflow_recommendation

Core Findings and Why They Matter

Chen et al. report several critical findings:

• High Prevalence of CEGs: 85.19% (46/54) of CREC isolates harbored at least one carbapenemase gene (Chen et al., 2025).
• blaNDM-1 Dominance: The blaNDM-1 gene was the most frequently detected, present in 33.33% (18/54) of isolates on both chromosomes and plasmids, and exclusively plasmid-borne in 46.30% (25/54).
• Other Genes: blaIMP was found in 3.70% (2/54; plasmid-only), and a single isolate (1.85%) carried both blaNDM-1 and blaKPC-2 on plasmids.
• Multidrug Resistance: CEG-positive isolates showed significantly higher resistance rates to imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin than CEG-negative strains (P<0.05).
• Efficient Gene Transfer: Plasmid conjugation experiments revealed a 95.65% (44/46) success rate for CEG transfer, with blaNDM-1 and blaIMP being highly transmissible.
• Mobile Genetic Elements: Six MGE types were identified, with ISEcp1 being most common (87.04%, 47/54). Notably, 40.74% (22/54) of isolates carried four MGE types simultaneously, suggesting robust platforms for gene exchange.
• Genotype Diversity: ERIC-PCR distinguished 17 genotypes, with type E and G each accounting for 20.37% (11/54). Type E isolates from different hospitals even shared a Dice coefficient of 100%, indicating clonal spread.
• Epidemiological Trends: CEGs were more frequent in male (64.81%), elderly (72.22%), respiratory medicine (20.37%), and sputum samples (33.33%).

These results highlight the clinical threat posed by highly transmissible, multidrug-resistant CREC, especially with the predominance of plasmid-borne blaNDM-1 and diverse MGE platforms facilitating rapid resistance spread (Chen et al., 2025).

Comparison with Existing Internal Articles

Several recent internal resources align with and extend the value of these findings:

• Optimizing Resistance Research with Amikacin (BAY416651) provides practical recommendations for using Amikacin as a bacterial protein synthesis inhibitor in resistance mechanism elucidation, including workflows for CREC and Klebsiella pneumoniae research. The protocols discussed therein support the kind of molecular resistance profiling performed in the Chen et al. study.
• Amikacin (BAY416651): Molecular Mechanisms and Experiment offers an in-depth perspective on aminoglycoside resistance pathways, particularly those involving enzymes such as AAC (6')-I, which are relevant given the multidrug resistance context revealed by Chen et al. This article further explains how Amikacin's resistance to many modifying enzymes makes it a robust comparator in functional antibiotic resistance assays.
• Amikacin (BAY416651) Aminoglycoside Antibiotic in Cell Assays discusses workflow optimization for cell viability and resistance assays, which dovetails with the broth microdilution approaches used in the reference study.

Together, these internal resources provide a methodological bridge and practical toolkit for translating the molecular epidemiology insights of the Guangdong CREC study into actionable laboratory protocols for antibiotic resistance research.

Limitations and Transferability

While Chen et al. provide detailed molecular and epidemiological data from eight large hospitals, several limitations merit consideration:

• Geographical Scope: All isolates were from Guangdong; patterns may differ in other regions or healthcare settings.
• Temporal Window: The study covers a specific post-pandemic period (2022–2024); resistance dynamics may evolve rapidly in response to changing clinical practices or antibiotic policies.
• Gene Focus: The analysis centers on major CEGs (blaNDM-1, blaIMP, blaKPC-2); emerging resistance determinants outside this panel could be missed.
• Assay Transferability: While protocols such as variable temperature SDS plasmid curing and ERIC-PCR are robust, their technical transferability depends on laboratory capacity and access to molecular reagents.

Nevertheless, the workflow and resistance profiling approaches are widely applicable for clinical microbiology laboratories globally.

Research Support Resources

For researchers aiming to replicate or extend resistance mechanism studies in CREC or Klebsiella pneumoniae, robust bacterial protein synthesis inhibitors such as Amikacin (BAY416651) Aminoglycoside Antibiotic (SKU B3431) are valuable tools. Amikacin is particularly suitable for functional resistance assays due to its resistance to most aminoglycoside-modifying enzymes and well-characterized activity against multidrug-resistant gram-negative bacteria (workflow_recommendation; product_spec). For detailed protocol optimization, including stock preparation and compatibility with resistance mechanism assays, see the referenced internal articles and APExBIO product documentation. This ensures antibiotic susceptibility testing is both reproducible and scientifically rigorous in the context of emerging resistance gene dynamics.