Deciphering Carbapenemase Transmission in Carbapenem-Resistant Enterobacter cloacae

Study Background and Research Question

Carbapenem-resistant Enterobacter cloacae (CREC) has emerged as a significant public health concern, particularly in tertiary care settings. The COVID-19 pandemic exacerbated challenges related to antimicrobial resistance, with increased antibiotic consumption and disrupted healthcare operations potentially accelerating the spread of resistant pathogens. CREC ranks as the third most detected carbapenem-resistant Enterobacteriaceae (CRE) in China, after Klebsiella pneumoniae and Escherichia coli. A central unresolved question is how carbapenemase-encoding genes (CEGs) are distributed and transmitted within CREC populations in hospital environments, and how these patterns have evolved during the pandemic.

Key Innovation from the Reference Study

This multicenter investigation is the first to systematically characterize both the molecular features and transmission dynamics of CEGs in CREC isolates from eight teaching hospitals in Guangdong province between December 2022 and June 2024. The study uniquely dissects the chromosomal and plasmid localization of key resistance determinants, evaluates their potential for horizontal gene transfer, and links these findings to clinical epidemiology, including patient demographics, sample sources, and hospital departments.

Methods and Experimental Design Insights

The research team collected 54 non-duplicate CREC isolates spanning eight diverse teaching hospitals. Molecular detection of CEGs—specifically blaNDM−1, blaIMP, and blaKPC−2—was performed using PCR assays on both chromosomal and plasmid DNA. The variable-temperature SDS plasmid elimination method facilitated analysis of gene localization. Horizontal gene transfer capability was assessed by plasmid conjugation experiments, while mobile genetic elements were profiled to understand potential vectors for gene dissemination. Genotyping of isolates employed ERIC-PCR and cluster analysis software (NTSYS), allowing detailed epidemiological mapping.

Protocol Parameters

• Sample collection: Non-duplicate CREC isolates from eight hospitals; December 2022–June 2024.
• CEG detection: PCR amplification targeting blaNDM−1, blaIMP, and blaKPC−2 on both chromosomes and plasmids.
• Plasmid elimination: Variable temperature SDS method to distinguish gene localization.
• Antimicrobial susceptibility: Broth microdilution for imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
• Gene transfer assessment: Conjugation experiments to test horizontal transfer rates of CEGs.
• Genotyping: ERIC-PCR and NTSYS clustering for strain relatedness.

Core Findings and Why They Matter

The study found that 85.19% of the CREC isolates harbored one or more carbapenemase-encoding genes. The blaNDM−1 gene was predominant, present on both chromosomes and plasmids in 33.33% of isolates, and exclusively on plasmids in 46.30%. The blaIMP gene was detected in 3.70%, while a small subset contained both blaNDM−1 and blaKPC−2. Notably, the presence of these genes on plasmids facilitated efficient horizontal transfer, with a conjugation success rate of 95.65% for CEGs—emphasizing the risk of rapid dissemination within hospital environments. Six mobile genetic element types were identified, with ISEcp1 being the most prevalent (87.04%), and over 40% of isolates carried four types simultaneously, further highlighting the complexity of resistance gene mobility.

Antimicrobial susceptibility testing revealed that CEG-positive isolates exhibited significantly higher resistance rates to multiple agents, including ciprofloxacin and levofloxacin, compared to CEG-negative isolates. This multidrug resistance pattern complicates treatment options and underscores the need for robust surveillance and infection control measures. Epidemiologically, CEGs were detected most frequently among male and elderly patients, within respiratory medicine departments, and in sputum samples, suggesting potential high-risk groups and clinical contexts for targeted interventions (see study details).

Comparison with Existing Internal Articles

Internal literature such as mechanistic reviews of Ciprofloxacin and its use as a research probe in antimicrobial resistance studies provide essential context for interpreting these findings. For example, ciprofloxacin—an established fluoroquinolone antibiotic—acts as a topoisomerase inhibitor, targeting DNA gyrase and topoisomerase IV, thereby inhibiting bacterial DNA replication. Its utility in resistance modeling is highlighted in several workflow guides (see applications), offering protocols for assessing resistance mechanisms and gene transfer dynamics in laboratory models.

While the reference study focuses on carbapenemase-encoding gene dynamics, the documented high resistance rates to ciprofloxacin among CEG-positive CREC isolates resonate with the broader concerns raised in these internal articles about the erosion of fluoroquinolone efficacy due to multidrug resistance. Moreover, the workflow optimizations described in cell-based assay protocols are directly relevant for researchers aiming to model or counteract resistance gene spread in similar experimental systems.

Limitations and Transferability

Despite its robust multicenter design, the study is limited by its sample size and geographical focus, potentially restricting generalizability to other regions or healthcare settings. The observational nature of the work precludes causal inference regarding specific transmission events. Additionally, while the molecular characterization of CEGs and mobile elements is comprehensive, functional studies on gene expression and clinical outcome correlations remain to be addressed. Nonetheless, the high horizontal transfer rates and prevalence of mobile elements observed suggest that the findings are transferable to other high-risk, high-density healthcare environments facing similar antimicrobial resistance pressures.

Research Support Resources

To facilitate laboratory modeling of fluoroquinolone resistance and topoisomerase inhibition in Enterobacteriaceae, researchers may employ Ciprofloxacin (SKU A8399), a high-purity fluoroquinolone antibiotic validated for DNA replication inhibition and resistance mechanism studies. APExBIO supplies this compound with quality confirmation by HPLC and NMR, supporting reproducible antimicrobial resistance workflows. For protocol guidance and advanced applications, consult internal articles on resistance modeling and workflow optimization referenced above.