Carbapenemase-Encoding Genes in Carbapenem-Resistant Enterobacter cloacae: Transmission Dynamics and Molecular Insights from Guangdong, China

Study Background and Research Question

Carbapenem-resistant Enterobacteriaceae (CRE) represent a growing global health concern, with Enterobacter cloacae (CREC) emerging as a significant contributor to nosocomial infections, particularly in China. The rise of carbapenem resistance, especially during the COVID-19 pandemic, has been exacerbated by increased antibiotic use and healthcare disruptions. Chen et al. (2025) address a critical gap: the molecular epidemiology and transmission dynamics of carbapenemase-encoding genes (CEGs) in CREC isolated from eight teaching hospitals in Guangdong between 2022 and 2024. Their investigation aims to clarify the prevalence of key resistance genes, their genetic contexts, and the mechanisms underpinning their rapid dissemination.

Key Innovation from the Reference Study

The central innovation of this study is its comprehensive mapping of CEG carriage—particularly blaNDM-1—across both chromosomal and plasmid backgrounds in clinical CREC isolates. It not only quantifies gene prevalence but also elucidates the efficiency of horizontal transfer and the diversity of mobile genetic elements involved. This dual focus enables a nuanced understanding of how multidrug resistance traits are propagated both within and between hospital settings, especially under pandemic pressures.

Methods and Experimental Design Insights

• Sample Collection: 54 CREC strains were collected from eight tertiary hospitals in Guangdong between December 2022 and June 2024, encompassing diverse departments and patient demographics.
• Molecular Characterization: PCR amplification and variable-temperature SDS plasmid curing were used to detect and localize CEGs (such as blaNDM-1, blaIMP, blaKPC-2) on plasmids and chromosomes.
• Antimicrobial Susceptibility: The broth microdilution method assessed resistance profiles to a panel of antibiotics, including imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
• Conjugation Experiments: Mating assays determined the transferability of CEGs between strains, with PCR confirmation of successful gene transfer.
• Mobile Genetic Element Identification: Six classes of elements, notably ISEcp1, were identified and quantified in association with CEGs.
• Genotyping: ERIC-PCR and NTSYS software classified isolates into 17 genotypes, tracking dissemination patterns across hospitals and departments.

Protocol Parameters

• Plasmid elimination via SDS: Applied at variable temperatures to distinguish chromosomal versus plasmid CEG localization.
• PCR cycling conditions: Optimized for high specificity in detecting multiple CEG variants within single isolates.
• Antibiotic susceptibility testing: Broth microdilution following CLSI guidelines to determine MICs for multidrug-resistant phenotypes.
• Conjugation assays: Donor and recipient strains co-incubated under selective pressure to evaluate horizontal gene transfer frequency.

Core Findings and Why They Matter

Analysis revealed an 85.19% prevalence of CEGs among the CREC isolates. The blaNDM-1 gene was the most frequently detected, present both on chromosomes and plasmids in 33.33% of isolates and exclusively on plasmids in an additional 46.30%. The blaIMP gene appeared in 3.70% of isolates, while co-carriage of blaNDM-1 and blaKPC-2 on plasmids was rare (1.85%). Notably, the CEG-positive group exhibited significantly higher resistance rates to multiple antibiotic classes compared to CEG-negative strains—a finding with immediate clinical implications for the treatment of complicated infections.

Plasmid conjugation experiments demonstrated a >95% success rate in transferring CEGs, emphasizing the profound capacity for horizontal dissemination. ISEcp1 was the most prevalent mobile element, detected in 87.04% of isolates, and many strains carried multiple mobile genetic elements simultaneously. Genotyping further revealed the predominance of types E and G, which were distributed across several hospitals and clinical departments, confirming inter-institutional transmission.

Epidemiological analysis indicated higher detection rates of CEG-positive CREC among male and elderly patients, in respiratory medicine units, and in sputum samples. This stratification provides actionable risk markers for targeted surveillance and infection control interventions.

Comparison with Existing Internal Articles

Findings from Chen et al. (2025) align with broader trends highlighted in recent analyses of antimicrobial resistance workflows. For example, "Dynamics of Carbapenemase Genes in Enterobacter cloacae During COVID-19" echoes the pandemic-driven acceleration of resistance gene dissemination, while "Tigecycline: Glycylcycline Antibiotic Workflows for Resistant Bacteria" discusses how advanced glycylcycline antibiotics are being incorporated into laboratory protocols to address the rising threat of multidrug-resistant Enterobacteriaceae. These complementary resources reinforce the need for molecular surveillance and innovative antimicrobial strategies in both research and clinical contexts.

Limitations and Transferability

Despite its strengths, the study's scope is limited by its geographic and temporal focus on eight hospitals in Guangdong during the COVID-19 era. While the high transferability of CEGs is clearly shown in vitro, real-world transmission dynamics may be influenced by unmeasured factors such as patient movement, antibiotic stewardship, and local infection control policies. Genotypic diversity and mobile element profiling provide robust strain-level insights, but further work is needed to correlate these findings with clinical outcomes and to generalize them beyond the studied region.

Research Support Resources

For laboratories investigating multidrug-resistant bacteria, the choice of antimicrobial agents is critical when designing in vitro and in vivo infection models. Tigecycline (SKU A5226) is a glycylcycline antibiotic with broad-spectrum activity, including efficacy against carbapenem-resistant and glycopeptide-intermediate pathogens. Its well-characterized mechanism as a 30S ribosomal subunit inhibitor, potent activity in both murine models and clinical isolates, and compatibility with standard resistance assays make it a valuable tool for translational research workflows. For detailed protocol optimization and troubleshooting in resistant strain studies, APExBIO provides validated product specifications and usage recommendations.