Characterization and Transmission Dynamics of Carbapenemase Genes in CREC

Study Background and Research Question

The escalating global threat posed by carbapenem-resistant Enterobacteriaceae (CRE) has sharpened the focus on Enterobacter cloacae, an opportunistic pathogen that ranks third among CRE isolates in China. The COVID-19 pandemic, with its attendant surge in antibiotic use and healthcare disruptions, has further exacerbated resistance challenges. Yet, until recently, detailed molecular epidemiology data on carbapenemase-encoding genes (CEGs) in carbapenem-resistant Enterobacter cloacae (CREC)—especially regarding their distribution and transmission dynamics in the post-pandemic era—remained scarce. The reference study addresses this gap by systematically investigating CEG profiles and their mobility across clinical isolates from multiple tertiary hospitals in Guangdong Province between 2022 and 2024.

Key Innovation from the Reference Study

The study's primary innovation lies in its concurrent high-resolution mapping of CEGs on both chromosomal and plasmid DNA in a clinical context spanning eight major hospitals. By doing so, it quantifies the distribution and transmissibility of resistance determinants, notably the blaNDM-1 gene, and correlates these with multidrug resistance phenotypes. This dual-level genetic mapping allows for nuanced understanding of both vertical (clonal spread) and horizontal (gene transfer) dynamics, which is vital for infection control and resistance modeling in antibacterial research.

Methods and Experimental Design Insights

Fifty-four non-duplicate CREC isolates were collected from December 2022 to June 2024. The researchers used variable temperature sodium dodecyl sulfate (SDS) plasmid elimination and PCR-based detection to localize and characterize CEGs. Resistance phenotyping was performed via broth microdilution, assessing susceptibility to imipenem and a spectrum of antibacterial agents. Plasmid conjugation experiments were employed to evaluate the transferability of CEGs, while ERIC-PCR typing and NTSYS software facilitated genotypic clustering and visualization of epidemiological patterns.

• Plasmid profiling and elimination enabled differentiation between chromosomal and mobile gene carriage, a methodological step crucial for tracking gene mobility.
• Conjugation assays provided functional proof of horizontal gene transfer potential for specific CEGs under laboratory conditions.
• Genotyping via ERIC-PCR revealed the clonal relationships and dissemination patterns across hospital departments.

Core Findings and Why They Matter

The study found a strikingly high prevalence (85.19%) of CEG-positive isolates among CREC. The blaNDM-1 gene predominated, with 33.33% of isolates harboring it on both chromosomes and plasmids, and an additional 46.30% carrying it exclusively on plasmids. This widespread plasmid association underscores the gene’s capacity for horizontal transfer, confirmed by a 95.65% success rate in plasmid-mediated CEG conjugation. Notably, the resistance rate in CEG-positive isolates to imipenem and other agents was significantly higher than in CEG-negative strains (P<0.05), as established by the study.

Six mobile genetic elements were identified, with ISEcp1 being the most prevalent (87.04%). The co-occurrence of multiple mobile elements within single isolates (notably, 40.74% carrying four types) reflects a robust genetic architecture for resistance dissemination. Genotypically, the strains were grouped into 17 clusters, with types E and G accounting for 40% of the isolates and exhibiting cross-departmental and cross-hospital spread—evidence for both clonal expansion and genetic exchange.

Epidemiologically, higher detection rates were observed in male patients (64.81%), the elderly (72.22%), within respiratory medicine departments (20.37%), and in sputum samples (33.33%). These findings inform both clinical surveillance and targeted antibacterial research design.

Comparison with Existing Internal Articles

Several prior resources, such as "Imipenem in Research: Bridging Antibacterial Action and Immunity" and "Imipenem: Semisynthetic Thienamycin Antibiotic for Research", have highlighted imipenem’s broad-spectrum activity and its role as a research tool in resistance modeling and immune response studies. These articles provide mechanistic insights into imipenem’s action on penicillin-binding proteins (PBPs) and its stability against beta-lactamases, establishing its value in both in vitro and in vivo workflows. However, the current reference study extends the field by mapping real-world clinical resistance determinants at a molecular level, directly linking gene localization and mobility to phenotypic resistance profiles. This complements earlier laboratory-focused discussions by contextualizing resistance evolution within active hospital networks.

Limitations and Transferability

While the study provides extensive molecular and epidemiological data, certain limitations remain. The sample set, though multi-institutional, is geographically restricted to Guangdong, and the study period is limited to the immediate post-pandemic window. Not all possible CEG subtypes or resistance mechanisms were exhaustively characterized. Laboratory conjugation experiments, while informative, may not fully recapitulate in vivo transfer dynamics. Nevertheless, the methods and findings are readily transferable to similar epidemiological surveillance in other regions and can inform experimental protocols in antibacterial research, especially for modeling plasmid-mediated resistance in gram-negative and gram-positive bacteria.

Protocol Parameters

• CREC isolate selection: Use fresh, non-duplicate clinical isolates; document source department and specimen type for epidemiological analysis.
• Plasmid elimination: Apply variable temperature SDS treatment to distinguish chromosomal from plasmid gene localization.
• CEG detection: Utilize PCR with primers specific for blaNDM-1, blaIMP, and blaKPC-2; confirm localization via sequencing if possible.
• Antibacterial susceptibility: Perform broth microdilution to assess resistance to imipenem and other agents as per CLSI guidelines.
• Conjugation assays: Implement filter mating protocol with appropriate recipient strains to test for plasmid transferability.
• Genotyping: Use ERIC-PCR for clonal analysis; cluster results with software such as NTSYS for strain typing.

Research Support Resources

Researchers aiming to model multidrug resistance or study the immunomodulatory effects of beta-lactam antibiotics can consider Imipenem (SKU P10075) as a validated tool for both in vitro and in vivo workflows. Imipenem’s well-characterized action against penicillin-binding proteins and proven stability, as outlined in the product information, align with the resistance mechanisms and experimental protocols highlighted in this study. APExBIO supplies research-grade imipenem suitable for protocols involving gram-negative and gram-positive bacteria, supporting further investigation into resistance dynamics and immune response modulation.