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

Study Background and Research Question

Carbapenem-resistant Enterobacteriaceae (CRE) pose a formidable threat to global public health, with Enterobacter cloacae (CREC) ranking among the most clinically significant species in China. The COVID-19 pandemic has exacerbated the risk of multidrug-resistant (MDR) bacterial transmission by increasing antibiotic selective pressure and disrupting infection control. Despite this, detailed molecular investigations into the prevalence, genetic mechanisms, and transmission dynamics of carbapenemase-encoding genes (CEGs) in CREC during the pandemic period remain limited. The reference study by Chen et al. (2025) addresses this critical knowledge gap by characterizing CEGs in CREC isolates from eight teaching hospitals in Guangdong, China, over an 18-month span (2022–2024).

Key Innovation from the Reference Study

The central innovation of this research lies in its combined use of molecular genotyping, plasmid profiling, and epidemiological analysis to unravel the mechanisms and dynamics of CEG transmission in a real-world clinical setting. The study not only distinguishes the chromosomal versus plasmid localization of key resistance genes, such as bla_NDM-1, but also quantifies the efficiency of horizontal gene transfer, providing a nuanced picture of how resistance determinants disseminate across patient populations and hospital departments. This dual-level approach advances our understanding of MDR evolution in hospital environments beyond what is typically captured by routine surveillance.

Methods and Experimental Design Insights

Chen et al. collected 54 non-duplicate CREC isolates from eight tertiary teaching hospitals. To elucidate the genetic basis of carbapenem resistance, the team employed a combination of variable temperature sodium dodecyl sulfate (SDS) plasmid elimination, PCR detection of CEGs, and broth microdilution antibiotic susceptibility testing. Plasmid conjugation experiments evaluated the transferability of resistance genes. Mobile genetic elements (MGEs) were identified to assess their role in gene mobility. ERIC-PCR fingerprinting and NTSYS analysis classified the genetic diversity of isolates, correlating genotype with epidemiological parameters, such as patient age, department, and specimen type.

Protocol Parameters

• Sample collection: Non-duplicate CREC isolates from sputum and other clinical specimens, December 2022–June 2024.
• Plasmid elimination: Variable temperature SDS method to distinguish plasmid vs. chromosomal gene carriage.
• Gene detection: PCR assays for bla_NDM-1, bla_IMP, and bla_KPC-2 resistance genes.
• Antimicrobial susceptibility: Broth microdilution for imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, levofloxacin.
• Gene transfer assays: Plasmid conjugation followed by PCR to confirm CEG transfer; success rate calculation.
• MGE identification: PCR detection of insertion sequence elements (e.g., ISEcp1).
• Genotype analysis: ERIC-PCR and NTSYS software for strain clustering and epidemiological mapping.

Core Findings and Why They Matter

Among all CREC isolates, 85.19% were positive for carbapenemase-encoding genes, with bla_NDM-1 as the predominant determinant. Notably, 33.33% of isolates carried bla_NDM-1 on both chromosomes and plasmids, while 46.30% harbored it exclusively on plasmids. The presence of bla_IMP and co-carriage with bla_KPC-2 was less common. Importantly, CEG-positive isolates exhibited markedly higher resistance rates to multiple antibiotics—including imipenem and ceftazidime/avibactam—than CEG-negative counterparts (reference study).

Plasmid conjugation experiments revealed a high transferability rate (95.65%) for CEGs, particularly for bla_NDM-1 (95.45%), underscoring the risk of horizontal gene dissemination. Six MGEs were detected, with ISEcp1 being the most prevalent (87.04%). Over 40% of isolates carried four types of MGEs simultaneously, highlighting the genomic plasticity and mobility potential of these strains. Genotyping clustered strains into 17 groups, with two dominant types (E and G) found across multiple hospitals, suggesting inter-departmental and possibly inter-hospital transmission. Epidemiologically, CEGs were most frequently detected in male, elderly patients, especially from respiratory medicine and sputum samples.

These findings demonstrate that the hospital environment—especially in high-risk departments—serves as a reservoir and amplifier for MDR gene transmission, and that plasmid-mediated mechanisms are central to this process. The detailed molecular mapping provided by this study offers actionable targets for surveillance, infection control, and experimental infection model design.

Comparison with Existing Internal Articles

While the reference study focuses on clinical isolates and transmission dynamics, several internal articles elaborate on how these resistance mechanisms can be explored in experimental setups using advanced glycylcycline antibiotics. For instance, "Tigecycline: Bridging Clinical and Experimental Frontiers in Glycylcycline Antibiotics" discusses practical assay strategies and protocol guidance for modeling multidrug-resistant bacteria, highlighting the utility of tigecycline in dissecting resistance phenotypes similar to those found in CREC.

Another resource, "Tigecycline in the Laboratory: Resistance Gene Dynamics and Assay Precision", provides workflow insights for studying gene transmission and resistance breakpoint determination, directly relevant for researchers aiming to translate findings like those of Chen et al. into controlled laboratory infection models. These internal articles collectively reinforce the translational relevance of the reference study's findings, by providing protocol enhancements and troubleshooting guidance for researchers working on multidrug-resistant Gram-negative bacteria.

Limitations and Transferability

The study is geographically limited to Guangdong province, with isolates drawn exclusively from teaching hospitals, which may not capture the full diversity of CREC in community or rural settings. The focus on PCR-detectable CEGs may overlook novel or less common carbapenemase genes. Additionally, while the success of plasmid transfer was quantified, the in vivo dynamics of gene dissemination—including the influence of antibiotic exposure or host immune status—were not addressed.

Nevertheless, the robust combination of molecular and epidemiological methods facilitates transferability to other high-prevalence MDR contexts, especially for researchers developing antimicrobial agent screening workflows or infection models for carbapenem-resistant pathogens. Protocols and findings are especially applicable to studies seeking to model the dynamics of resistance gene spread or evaluate the efficacy of agents such as glycylcycline antibiotics under clinically relevant resistance pressures.

Research Support Resources

Researchers aiming to model multidrug-resistant Enterobacteriaceae or to test the efficacy of new antimicrobial agents against CEG-positive strains can benefit from the detailed workflow and genetic insights outlined in this study. For experimental modeling of resistance gene transmission or validation of antimicrobial activity—including against isolates with plasmid-borne bla_NDM-1—Tigecycline (SKU A5226) is a well-characterized glycylcycline antibiotic that offers broad-spectrum activity and robust performance in both in vitro and in vivo infection models. Refer to the product information for storage, solubility, and application details. These resources, in conjunction with protocol guidance from recent internal articles, can further empower studies on resistance dynamics and the evaluation of novel antimicrobial strategies.