Transmission Dynamics of Carbapenemase Genes in CREC: Insights from Eight Hospitals in Guangdong

Study Background and Research Question

Carbapenem-resistant Enterobacteriaceae (CRE) have emerged as a critical public health threat, with carbapenem-resistant Enterobacter cloacae (CREC) ranking among the most prevalent species in clinical settings. The COVID-19 pandemic has further complicated antimicrobial resistance landscapes due to increased antibiotic consumption, healthcare disruptions, and complex co-infections. However, there is a paucity of detailed molecular epidemiological data on the characteristics and dissemination of carbapenemase-encoding genes (CEGs) in CREC during this period. The reference study by Chen et al. (BMC Microbiology, 2025) addresses this gap by systematically characterizing the prevalence, genetic context, and transmission dynamics of CEGs among clinical CREC isolates in Guangdong Province, China, from 2022 to 2024.

Key Innovation from the Reference Study

The central innovation of this work lies in its comprehensive assessment of both chromosomal and plasmid-borne CEGs within CREC isolates, with a focus on the bla_NDM-1 gene and its mobility. Unlike previous studies limited to phenotypic surveillance or narrow gene panels, Chen et al. combine PCR-based genotyping, plasmid elimination, and conjugation assays to elucidate both the genetic context and the real-world transmission potential of resistance determinants. This multidimensional approach enables the mapping of horizontal gene transfer capacity and the identification of prevalent mobile genetic elements, directly informing infection control and antimicrobial stewardship efforts.

Methods and Experimental Design Insights

The study analyzed 54 non-duplicate CREC isolates collected from eight teaching hospitals over an 18-month period. Key methodological features include:

• Genetic Analysis: Variable temperature SDS plasmid curing was used to differentiate chromosomal and plasmid localization of CEGs. Conventional PCR targeted the most clinically relevant carbapenemase genes: bla_NDM-1, bla_IMP, and bla_KPC-2.
• Antimicrobial Susceptibility Testing: The broth microdilution method evaluated resistance profiles for both CEG-positive and CEG-negative isolates against key antibiotics such as imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
• Conjugation Experiments: Plasmid transferability was assessed through mating assays, with PCR confirmation of CEG acquisition in recipient strains.
• Mobile Genetic Element Typing: Six types of mobile elements were screened, with special attention to the prevalence and combinatorial arrangements of insertion sequences.
• Genotyping: ERIC-PCR and NTSYS clustering enabled epidemiological tracking of strain relatedness and the spread of dominant genotypes.

Core Findings and Why They Matter

The study yielded several critical insights:

• High Prevalence and Mobility of bla_NDM-1: Among 54 CREC isolates, 33.33% harbored bla_NDM-1 on both chromosomes and plasmids, and 46.30% carried it exclusively on plasmids. Only a small fraction (3.70%) had bla_IMP alone, and an even smaller subset (1.85%) contained both bla_NDM-1 and bla_KPC-2.
• Resistance Phenotypes: The CEG-positive group displayed significantly higher resistance rates to all tested antibiotics compared to CEG-negative strains, underscoring the clinical impact of these genes (reference study).
• Efficient Horizontal Transfer: Plasmid conjugation experiments demonstrated a 95.65% success rate for CEG transfer, with bla_NDM-1 and bla_IMP showing near-complete transmissibility. This highlights the high risk of rapid resistance dissemination within healthcare environments.
• Mobile Genetic Elements: Six element types were identified, with ISEcp1 being most prevalent (87.04%). Notably, 40.74% of isolates carried four types simultaneously, suggesting a complex mosaic of mobile resistance determinants.
• Epidemiological Hotspots: The detection rate of CEGs was highest among male and elderly patients, particularly in respiratory medicine departments and sputum samples. Genotyping clustered 54 isolates into 17 groups, with two types (E and G) dominating across multiple hospitals and departments—indicating both clonal and horizontal transmission routes.

These findings have immediate implications for infection control, as they reveal both the molecular mechanisms of resistance and the practical avenues for inter-strain and inter-hospital gene flow. The rapid, widespread transferability of plasmid-borne CEGs, especially bla_NDM-1, signals a pressing need for enhanced surveillance and stewardship protocols.

Comparison with Existing Internal Articles and Broader Context

Internal resources, such as Carbapenemase Genes in CREC: Dynamics and Transmission in Guangdong, echo the present study’s focus on the genetic mapping and epidemiological tracking of resistance determinants. However, the current reference work distinguishes itself through the integration of real-time conjugation data and detailed mobile element profiling, providing a more granular look at transmission mechanisms.

Whereas resources like Tigecycline in the Genomic Era and Tigecycline Workflows for Multidrug-Resistant Bacteria Research concentrate on experimental design and assay optimization for multidrug-resistant bacteria—including methicillin-resistant Staphylococcus aureus (MRSA) and glycopeptide-intermediate Staphylococcus aureus (GISA)—the present study is rooted in clinical epidemiology and genetic surveillance. Together, these domains bridge the gap between molecular characterization and bench-to-bedside translational workflows, especially for researchers interested in antimicrobial agents for multidrug-resistant bacteria.

Limitations and Transferability

The study is limited by its sample size (54 isolates) and regional focus (eight hospitals in Guangdong Province), which may constrain the generalizability of its epidemiological findings. Moreover, the investigation is cross-sectional, capturing a specific time window influenced by pandemic-related healthcare dynamics. Functional validation of CEG expression levels and fitness costs was not directly addressed. Nevertheless, the clear demonstration of high-frequency plasmid transfer and mobile element diversity provides a robust framework for similar molecular surveillance studies in other geographies and healthcare settings.

Protocol Parameters

• Sample collection period: December 2022 – June 2024; ensure time frame aligns with pandemic-related resistance trends.
• Plasmid elimination: Utilize variable temperature SDS curing for effective differentiation of chromosomal versus plasmid-borne CEGs.
• PCR target selection: Include bla_NDM-1, bla_IMP, and bla_KPC-2 to capture clinically relevant resistance genes.
• Conjugation assay: Confirm transferability of CEGs with post-conjugation PCR in recipient strains; consider a minimum of 40 isolates for reliable estimation.
• Genotyping: Apply ERIC-PCR and cluster analysis to map epidemiological relationships among isolates.
• Antimicrobial susceptibility testing: Use broth microdilution methods for comprehensive resistance profiling; compare CEG-positive and negative groups.

Research Support Resources

For researchers aiming to model resistance transfer, evaluate novel interventions, or screen alternative antimicrobial agents for multidrug-resistant bacteria, robust in vitro systems and reference compounds are essential. Tigecycline (SKU A5226) from APExBIO, as a glycylcycline antibiotic with broad-spectrum activity and proven performance in both in vitro and in vivo MDR models, offers a reliable standard for comparative assays—including those targeting CREC and other challenging pathogens. When designing workflows for the treatment of complicated skin and skin-structure infections or deploying bacteriostatic protein synthesis inhibitors, validated reagents like Tigecycline can help ensure experimental reproducibility and translational relevance.