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

Study Background and Research Question

The global rise of carbapenem-resistant Enterobacteriaceae (CRE) has intensified the clinical and public health challenge of multidrug-resistant (MDR) bacterial infections. Among CRE, Enterobacter cloacae has emerged as a major contributor to hospital-acquired infections in China, with increasing detection rates across clinical departments. The COVID-19 pandemic further complicated this landscape by increasing antibiotic use and hospital transmission risks, thereby promoting the emergence and spread of drug-resistant bacteria. Yet, comprehensive investigations into the prevalence, genetic characteristics, and transmission patterns of carbapenemase-encoding genes (CEGs) in carbapenem-resistant E. cloacae (CREC) during this period have been limited. The reference study (Chen et al., 2025) addresses this gap by systematically analyzing CREC isolates from eight teaching hospitals in Guangdong, China, collected between December 2022 and June 2024.

Key Innovation from the Reference Study

The central innovation of Chen et al. (2025) lies in its comprehensive, multi-site molecular epidemiology of CEGs in CREC during the COVID-19 pandemic. The study not only quantifies the prevalence and diversity of resistance genes—most notably bla_NDM-1, bla_IMP, and bla_KPC-2—but also dissects their chromosomal and plasmid localization, horizontal transfer rates, and association with mobile genetic elements. By integrating genotyping (ERIC-PCR), epidemiological surveillance, and resistance profiling, the authors elucidate both the scope and mechanisms underlying rapid dissemination of multidrug resistance within and between hospital environments.

Methods and Experimental Design Insights

The study analyzed 54 non-redundant CREC isolates from eight geographically dispersed teaching hospitals. The workflow included:

• Genetic Detection: Variable temperature SDS plasmid elimination and PCR assays were used to identify and localize CEGs on chromosomes and plasmids.
• Phenotypic Resistance Profiling: The broth microdilution method quantified susceptibility to a panel of antibiotics, including imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
• Conjugation Experiments: Plasmid transferability of CEGs was assessed through conjugation assays and subsequent PCR confirmation in recipient strains.
• Mobile Genetic Element Typing: Identification of insertion sequence elements (notably ISEcp1) was performed to investigate genetic mobility.
• Genotyping and Epidemiological Analysis: ERIC-PCR and NTSYS clustering enabled determination of genotype diversity and prevalence, while demographic and clinical metadata informed epidemiological patterns.

This integrated approach allowed the authors to correlate molecular features with clinical and epidemiological variables, providing a layered understanding of resistance gene spread.

Core Findings and Why They Matter

The study’s principal findings reveal the scale and mechanisms of multidrug resistance in CREC isolates:

• High CEG Prevalence: 85.19% (46/54) of CREC isolates carried at least one CEG, with bla_NDM-1 being predominant. Notably, 33.33% harbored bla_NDM-1 on both chromosomes and plasmids, while 46.30% carried it exclusively on plasmids.
• Plasmid-Mediated Dissemination: Plasmid conjugation experiments demonstrated a 95.65% success rate for horizontal transfer of CEGs, with the highest rates for bla_NDM-1 (95.45%) and bla_IMP (100%). bla_KPC-2 was rare and not successfully transferred in vitro.
• Mobile Genetic Elements: Six types of mobile elements were detected, with ISEcp1 identified in 87.04% of isolates, highlighting its role in facilitating gene mobility. 40.74% of CREC isolates carried four types of mobile elements simultaneously.
• Genotypic and Epidemiological Diversity: ERIC-PCR classified the isolates into 17 genotypes, with types E and G being the most widespread across clinical departments and hospitals. The highest detection rates occurred among male and elderly patients, particularly in respiratory medicine and sputum samples (64.81%, 72.22%, 20.37%, and 33.33%, respectively).
• Multidrug Resistance Profiles: CEG-positive isolates exhibited significantly higher resistance rates to multiple antibiotics, including key agents such as imipenem and cefepime (Chen et al., 2025), underscoring the clinical threat posed by these strains.

These findings collectively demonstrate that plasmid-mediated horizontal transfer, facilitated by common mobile genetic elements, is a dominant driver of rapid MDR gene dissemination in hospital settings. The predominance of bla_NDM-1—a gene associated with resistance to nearly all beta-lactam antibiotics—places additional pressure on infection control and antimicrobial stewardship efforts.

Comparison with Existing Internal Articles

Several recent internal reviews and research summaries corroborate and contextualize these findings. For example, the article "Transmission Dynamics of Carbapenemase Genes in CREC in China" highlights the high prevalence and rapid spread of CEGs—particularly plasmid-borne bla_NDM-1—across multiple hospitals, reinforcing the core message of the reference study. Similarly, "Cefotaxime as a Strategic Tool in Translational Antimicro..." explores the application of third-generation cephalosporins in resistance modeling, emphasizing the relevance of beta-lactamase-resistant agents in studies of horizontal gene transfer and multidrug resistance mechanisms. The current reference study advances this literature by providing a granular, genotype- and phenotype-linked map of resistance gene transmission, filling critical knowledge gaps about how MDR determinants circulate within and between clinical settings.

Protocol Parameters

• Isolate Collection: 54 non-redundant CREC isolates from eight teaching hospitals, sampled December 2022–June 2024.
• Genetic Testing: PCR amplification for bla_NDM-1, bla_IMP, bla_KPC-2; plasmid vs. chromosomal localization confirmed with variable temperature SDS curing.
• Resistance Phenotyping: Broth microdilution method for imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, levofloxacin.
• Plasmid Transfer Assays: Conjugation experiments to assess horizontal transfer rates of CEGs, followed by PCR confirmation in transconjugants.
• Mobile Element Typing: PCR-based identification of mobile genetic elements, notably ISEcp1.
• Genotyping: ERIC-PCR and cluster analysis with NTSYS software.
• Demographic/Epidemiological Analysis: Stratification by gender, age, hospital department, and specimen type.

Limitations and Transferability

While the study offers detailed molecular and epidemiological insights, several limitations should be acknowledged. The surveillance cohort, though multi-center, is geographically restricted to Guangdong and may not capture regional or global diversity in CREC genotypes or CEG variants. The observational window (2022–2024) aligns with the COVID-19 pandemic, potentially influencing antibiotic use patterns and transmission dynamics in ways that may differ from pre- or post-pandemic contexts. Additionally, in vitro conjugation assays may not fully recapitulate the complexity of gene transfer in vivo. Nonetheless, the methods and findings are transferable to other hospital settings seeking to map MDR gene transmission, and the molecular protocols can be adapted for broader antimicrobial resistance research and bacterial infection modeling.

Research Support Resources

For researchers modeling multidrug resistance or studying beta-lactam antibiotic mechanisms in Gram-positive and Gram-negative bacterial infections, validated reference compounds are essential. Cefotaxime (SKU BA1012) from APExBIO is a third-generation cephalosporin antibiotic with robust activity against both Gram-negative and Gram-positive bacteria, and resistance to beta-lactamase enzymes. Its properties facilitate detailed investigation of antimicrobial resistance mechanisms and support the development of bacterial infection models. When preparing experimental workflows, solutions of Cefotaxime should be used freshly as recommended to preserve efficacy. While not intended for therapeutic or diagnostic use, this resource can underpin studies on horizontal gene transfer, resistance profiling, and screening for novel antimicrobial interventions.