Transmission Dynamics of Carbapenemase Genes in Enterobacter cloacae: Insights from Guangdong Hospitals

Study Background and Research Question

Carbapenem-resistant Enterobacteriaceae (CRE) pose a growing public health threat, with Enterobacter cloacae emerging as a critical Gram-negative pathogen in clinical settings. The COVID-19 pandemic has further complicated antimicrobial stewardship due to increased antibiotic use and healthcare service interruptions, raising concerns about resistance proliferation. Despite this, detailed surveillance of carbapenemase-encoding genes (CEGs) in carbapenem-resistant Enterobacter cloacae (CREC) and shifts in their transmission dynamics during the pandemic have been limited. Addressing this gap, Chen et al. (2025) examined the prevalence, genetic localization, and transmission dynamics of CEGs among CREC isolates collected from eight teaching hospitals in Guangdong Province, China, between December 2022 and June 2024 (paper).

Key Innovation from the Reference Study

The principal innovation of this work lies in its simultaneous genotypic and epidemiological characterization of CEGs, with an emphasis on plasmid-mediated versus chromosomal gene localization during a pandemic context. Notably, the study quantifies the prevalence of specific CEGs (including blaNDM-1, blaIMP, and blaKPC-2) and their association with multidrug resistance phenotypes. By integrating molecular assays, conjugation experiments, and epidemiological data, the authors provide a granular understanding of horizontal and vertical gene transmission in a real-world, multicenter hospital setting (paper).

Methods and Experimental Design Insights

A total of 54 CREC isolates were collected from diverse clinical departments and specimen types across eight tertiary hospitals. The study utilized:

• Variable temperature SDS plasmid elimination and PCR to detect and localize CEGs on plasmid and chromosomal DNA.
• Broth microdilution for antimicrobial susceptibility testing across multiple antibiotics.
• ERIC-PCR and NTSYS software for genotypic clustering and epidemiological mapping.
• Plasmid conjugation experiments to assess horizontal gene transfer efficiency.

This multipronged approach enabled precise measurement of gene prevalence, resistance rates, and dissemination potential within hospital networks (paper).

Core Findings and Why They Matter

The study reports an exceptionally high rate (85.19%) of CEG positivity among CREC isolates, with the blaNDM-1 gene as the predominant resistance determinant. The gene was found on both chromosomes and plasmids in 33.33% of isolates, exclusively on plasmids in 46.30%, and rarely co-localized with blaKPC-2 or blaIMP. Most strikingly, the resistance rates to key antibiotics—including imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin—were significantly higher in CEG-positive strains (source: paper). Plasmid conjugation experiments showed a 95.65% success rate for CEG transfer, with blaNDM-1 and blaIMP genes transferring at particularly high frequencies, underscoring the robust horizontal dissemination potential of these resistance determinants. Six major mobile genetic elements (MGEs) were identified, with ISEcp1 being the most prevalent (87.04%). The data also reveal epidemiological hotspots: higher detection rates in male and elderly patients, within respiratory medicine departments, and in sputum samples, aligning with the increased burden of treatment-resistant respiratory infections during the pandemic period (paper).

Protocol Parameters

• antibiotic susceptibility testing | broth microdilution, CLSI guidelines | multidrug resistance assessment | enables standardized comparison of resistance phenotypes | paper
• CEG localization | PCR, SDS-plasmid elimination | genotypic mapping | distinguishes plasmid vs. chromosomal gene carriage | paper
• gene transferability | conjugation assay, 37°C, 4-24 hr | horizontal transfer potential | quantifies MGE-driven dissemination | paper
• molecular typing | ERIC-PCR, NTSYS analysis | epidemiological surveillance | identifies clonal spread and diversity | paper
• plasmid stability under laboratory storage | -20°C | experimental reproducibility | maintains genetic integrity over time | workflow_recommendation

Comparison with Existing Internal Articles

These findings complement previous internal analyses, such as "Carbapenemase Genes in Enterobacter cloacae: Resistance Dynamics in Guangdong Hospitals," which also highlighted the dominance of plasmid-mediated blaNDM-1 and the urgent need for improved resistance monitoring (internal article). Similarly, the article "Transmission of Carbapenemase Genes in CREC During COVID-19" reinforces the notion that the pandemic environment accelerates horizontal resistance gene transfer, creating new challenges for Gram-negative bacterial infection research and the treatment of bacterial pneumonia (internal article). Further, internal resources on third-generation cephalosporins, such as "Ceftazidime: Advanced Insights into β-Lactamase Resistance," provide necessary context for understanding the clinical and experimental role of β-lactamase resistant cephalosporins in combating multidrug-resistant pathogens, including Pseudomonas aeruginosa and Enterobacter spp. (internal article).

Limitations and Transferability

While the study offers robust, multicenter data, its findings are geographically limited to Guangdong Province and a relatively short pandemic-era timespan. The sample size, while significant, may not capture the full genetic variability present in other regions or in the post-pandemic era. Additionally, while the focus on CEGs provides actionable insight for infection control, the work does not address the full spectrum of resistance mechanisms or emerging plasmid incompatibility groups. Transferability of protocols—such as PCR-based gene localization and broth microdilution—remains high for research laboratories worldwide but requires local validation.

Research Support Resources

Researchers investigating resistance mechanisms or designing protocols for Gram-negative bacterial infection research can utilize third-generation cephalosporins such as Ceftazidime (SKU B3539, APExBIO) for experimental validation of susceptibility phenotypes or resistance development. Ceftazidime is well-characterized for its broad spectrum activity, including efficacy against Pseudomonas aeruginosa and resistance to β-lactamases, making it a practical choice for benchmarking laboratory assays and supporting translational studies in multidrug resistance (product_spec). For optimal results, ensure storage at -20°C and use freshly prepared stock solutions to preserve compound integrity (workflow_recommendation).