Carbapenemase-Encoding Genes in Carbapenem-Resistant Enterobacter cloacae: Insights from Guangdong’s Multicenter Study

Study Background and Research Question

Carbapenem-resistant Enterobacter cloacae (CREC) has emerged as a major public health concern, ranking third among carbapenem-resistant Enterobacteriaceae in China after Klebsiella pneumoniae and Escherichia coli. The COVID-19 pandemic has amplified antimicrobial resistance challenges, with increased antibiotic use and healthcare disruptions fostering the emergence and spread of multidrug-resistant organisms. Despite a global rise in CREC prevalence, detailed molecular studies on carbapenemase-encoding genes (CEGs) and their transmission patterns—especially in the context of pandemic-driven healthcare changes—remain limited (source). The present study addresses these gaps by characterizing CEGs and their dynamics in CREC strains isolated from eight major teaching hospitals in Guangdong Province between December 2022 and June 2024 (paper).

Key Innovation from the Reference Study

A central advance of this work is its comprehensive mapping of both the prevalence and mobility of CEGs in clinical CREC isolates during the COVID-19 era. By integrating plasmid elimination, conjugation experiments, and genotyping, the study quantifies not only the frequency but also the transferability of key resistance determinants (notably blaNDM-1, blaIMP, and blaKPC-2). The research provides a nuanced view of how these genes are distributed across both plasmids and chromosomes, and how mobile genetic elements (MGEs) facilitate their rapid dissemination within healthcare settings (paper).

Methods and Experimental Design Insights

The investigators collected 54 non-duplicate CREC isolates from eight teaching hospitals, using variable temperature sodium dodecyl sulfate (SDS) plasmid elimination methods and polymerase chain reaction (PCR) assays to screen for CEGs. The location of these genes (chromosomal vs. plasmid) was delineated, and their transferability was tested via broth microdilution and plasmid conjugation experiments. Mobile genetic elements were typed, and ERIC-PCR coupled with NTSYS software enabled high-resolution genotyping to trace epidemiological relatedness (paper).

Protocol Parameters

• antibiotic susceptibility assay | broth microdilution, MIC range per CLSI guidelines | applicable to clinical and experimental isolates | enables direct resistance profiling of CREC strains | paper
• plasmid elimination method | variable temperature SDS | applicable to Enterobacteriaceae | discriminates chromosomal versus plasmid gene carriage | paper
• gene detection | PCR, primers for blaNDM-1, blaIMP, blaKPC-2 | broad for Enterobacteriaceae | sensitive and specific detection of key resistance genes | paper
• mobile genetic element typing | PCR and sequencing, 6 MGE types (ISEcp1 etc.) | Enterobacteriaceae, especially CREC | tracks horizontal gene transfer drivers | paper
• ERIC-PCR genotyping | 17 genotypes discerned | epidemiological tracing in hospital outbreaks | high-resolution strain discrimination | paper

Core Findings and Why They Matter

The study uncovered a strikingly high CEG positivity rate (85.19%, 46/54 isolates), with blaNDM-1 emerging as the dominant gene. Notably, 33.33% of isolates carried blaNDM-1 on both chromosomes and plasmids, and 46.30% had it exclusively on plasmids. The rapid horizontal transfer potential was underscored by a 95.65% success rate in conjugation experiments for CEGs, with blaNDM-1 and blaIMP being particularly mobile (paper). Six MGEs were identified, with ISEcp1 present in 87.04% of isolates—highlighting the central role of MGEs in gene dissemination. Antibiotic resistance profiling revealed that CEG-positive CREC strains demonstrated significantly higher resistance rates to imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin compared to CEG-negative strains (P<0.05) (paper). Genotyping clustered isolates into 17 types, with E and G being most prevalent, and revealed inter-hospital and multi-department transmission chains. Epidemiological analysis identified elderly male patients, respiratory medicine departments, and sputum specimens as the highest risk groups for CEG detection, informing targeted infection control priorities.

Comparison with Existing Internal Articles

Recent internal reviews expand the broader context of this study:

• The article "Transmission Dynamics of Carbapenemase Genes in CREC: Guangdong Study" echoes the multicenter approach, emphasizing the urgent need for robust resistance surveillance and providing methodological blueprints for future research on transmission and molecular diagnostics.
• "Levofloxacin: Advanced Mechanistic Insights for Antibacterial Research" contextualizes the relevance of resistance mechanisms by focusing on levofloxacin, a synthetic fluoroquinolone antibiotic, as a model system for studying both bacterial DNA replication pathways and resistance emergence. These insights support the use of levofloxacin in multidrug resistance and susceptibility assays, connecting the present study’s findings to practical laboratory workflows.
• For workflows that require direct application of resistance profiling or osteoblast growth inhibition assays, "Levofloxacin (SKU B1959): Reliable Workflows for Antibacterial Resistance" offers scenario-driven protocols for leveraging levofloxacin in cell-based and biochemical assays, bridging the gap between molecular findings and experimental design.

Limitations and Transferability

While the study provides robust multicenter data, several limitations should be noted. The research is geographically constrained to Guangdong Province and teaching hospitals, which may not represent rural or primary care settings. The focus on a limited number of CEGs, primarily blaNDM-1, blaIMP, and blaKPC-2, leaves out other emerging resistance determinants. Furthermore, the observational window (2022–2024) coincides with pandemic-specific healthcare disruptions, which may not reflect longer-term trends (paper). Despite these constraints, the methodological frameworks—plasmid elimination, conjugation assays, and genotyping—are readily transferable to other Enterobacteriaceae and resistance gene studies, particularly for researchers designing osteoblast growth inhibition assays or chondrocyte glycosaminoglycan synthesis studies in the context of antibiotic resistance (internal_article).

Research Support Resources

To replicate or expand upon these experimental workflows, researchers may require validated antibiotic agents for susceptibility and mechanistic studies. Levofloxacin (SKU B1959), available from APExBIO, is a synthetic fluoroquinolone antibiotic that inhibits bacterial DNA gyrase, making it suitable for bacterial DNA replication pathway studies, osteoblast growth inhibition assays, and calcium deposition inhibition workflows. Its use is well-documented in both resistance profiling and bone metabolism research; for optimal results, follow product-specific solubility and storage recommendations (source: product_spec).