Characterization of Carbapenemase Genes in CREC: Insights from Guangdong Teaching Hospitals (2022–2024)

Study Background and Research Question

Carbapenem-resistant Enterobacteriaceae (CRE) represent a global threat to clinical care, with Enterobacter cloacae listed as a leading cause of multidrug-resistant infections in China. The COVID-19 pandemic, with its unprecedented strain on healthcare systems, has intensified concerns about antibiotic resistance due to increased antibiotic use and more complex patient cases. However, granular studies examining the characteristics and transmission patterns of carbapenemase-encoding genes (CEGs) in carbapenem-resistant Enterobacter cloacae (CREC) during this period have been limited. The present study addresses this gap by investigating the molecular epidemiology, gene localization, and transmission potential of CEGs in CREC isolates collected from eight tertiary hospitals in Guangdong province between late 2022 and mid-2024 (paper).

Key Innovation from the Reference Study

This work provides a comprehensive multi-center snapshot of CEG prevalence and mobility in CREC across a critical pandemic window. The most notable innovation is the simultaneous mapping of CEG locations (plasmid vs. chromosomal), quantification of horizontal gene transfer potential via conjugation experiments, and integration of genotyping with clinical epidemiology. The focus on blaNDM-1 and its frequent plasmid localization underscores the risk of rapid resistance dissemination. Additionally, the study systematically connects molecular findings with patient demographics and clinical departments—a rarely unified approach in the literature (paper).

Methods and Experimental Design Insights

Fifty-four non-duplicate CREC isolates were collected prospectively from eight hospitals. The following experimental approaches underpinned the analysis:

• Variable Temperature SDS Plasmid Elimination and PCR: Used to determine the presence and genetic localization (plasmid or chromosomal) of carbapenemase-encoding genes.
• Broth Microdilution Susceptibility Testing: Assessed resistance profiles to key antibiotics, including imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
• Conjugation Experiments: Quantified the efficiency of CEG horizontal transfer between strains.
• ERIC-PCR and Genotyping: Clustered isolates into genotypes and analyzed transmission links using NTSYS software.
• Mapping of Mobile Genetic Elements: Identified types and combinations of genetic elements facilitating CEG mobility.

This robust, multi-pronged methodology enabled high-resolution tracking of resistance gene dynamics.

Core Findings and Why They Matter

The study produced several impactful findings:

• High Prevalence of CEGs: 85.19% of CREC isolates harbored CEGs, with blaNDM-1 being the most common (source: paper).
• Gene Localization: 33.33% of isolates carried blaNDM-1 on both chromosomes and plasmids; 46.3% had it exclusively on plasmids. A small subset possessed blaIMP or both blaNDM-1 and blaKPC-2 on plasmids (source: paper).
• High Rates of Horizontal Transfer: Conjugation experiments demonstrated a 95.65% transfer success for CEGs, with near 100% for blaNDM-1 and blaIMP, highlighting the threat of rapid spread (source: paper).
• Mobile Genetic Elements Fuel Spread: Six types of mobile elements were detected, with ISEcp1 being most prevalent (87.04%). Notably, 40.74% of isolates carried four types simultaneously, amplifying transmission risk (source: paper).
• Multidrug Resistance: CEG-positive isolates had significantly higher resistance to multiple antibiotics, including imipenem (source: paper).
• Epidemiological Insights: CEG detection was most frequent in men, elderly patients, respiratory departments, and sputum samples, providing targets for surveillance (source: paper).

These findings reinforce the urgency of monitoring plasmid-mediated resistance and tailoring infection control to high-risk patient populations and clinical contexts.

Protocol Parameters

• broth microdilution assay | variable, e.g., imipenem concentration 30–60 mg/L | in vitro resistance profiling | Standard for assessing susceptibility and resistance levels in CREC | paper
• conjugation experiment | transfer frequency 95.65% (CEGs) | in vitro gene mobility testing | Demonstrates real-world risk of horizontal resistance gene transfer | paper
• PCR-based detection | qualitative (presence/absence of CEGs) | molecular epidemiology | Enables precise identification of gene localization | paper

Comparison with Existing Internal Articles

Several internal articles provide complementary perspectives to the current study:

• "Imipenem in Experimental Resistance: Mechanisms, Dynamics, and Immune Modulation" explores how imipenem, as a semisynthetic thienamycin antibiotic, interacts with resistance mechanisms, including plasmid dynamics. The article’s focus on molecular mechanisms and resistance gene transmission aligns directly with the reference study’s findings on horizontal CEG transfer.
• "Imipenem in Multidrug Resistance: Plasmid Dynamics and Research Implications" provides advanced insights into plasmid-mediated resistance and assay design, reinforcing the importance of monitoring CEGs in clinical isolates, as highlighted by the reference study.
• "Imipenem: Mechanistic Advances and New Horizons in Antibacterial Research" details protocols for PBP inhibition and immune modulation, supporting the translational relevance of molecular findings in CREC resistance modeling.

Together, these resources contextualize the reference study’s results within broader antibacterial research, highlighting the enduring research value of semisynthetic thienamycin antibiotics like imipenem in resistance surveillance and experimental modeling.

Limitations and Transferability

Despite its strengths, this study has several limitations. The sample size, while multi-center, remains regionally focused and may not capture the full genetic diversity of CREC in other provinces or countries. The absence of detailed clinical outcome data constrains direct translation to patient management. Furthermore, while the study demonstrates high rates of CEG transfer in vitro, real-world transfer dynamics may differ due to host, microbiome, and environmental factors (source: paper). However, the molecular and methodological framework is readily transferable to other settings, providing a blueprint for future surveillance of gram-negative and gram-positive bacteria with complex resistance patterns.

Research Support Resources

For investigators aiming to replicate or extend this work, reliable research reagents are essential. Imipenem (SKU P10075) from APExBIO, a semisynthetic thienamycin antibiotic with well-characterized activity against a broad spectrum of gram-negative and gram-positive bacteria, can support susceptibility testing, resistance modeling, and immune response assays (source: product_spec). Its stability and defined mechanism—high affinity for penicillin-binding proteins (PBPs) and resistance to many beta-lactamases—make it a foundational tool for contemporary antibacterial research. Researchers are encouraged to consult APExBIO for detailed compound specifications and workflow recommendations tailored to high-containment microbiology and resistance surveillance.