Characterizing Carbapenemase Gene Transmission in CREC: Insights from a Multi-Hospital Study in Guangdong

Study Background and Research Question

Carbapenem-resistant Enterobacter cloacae (CREC) has rapidly emerged as a significant clinical threat, ranking among the top Enterobacteriaceae in multidrug-resistant (MDR) infections in China. The global COVID-19 pandemic has aggravated this problem through increased antibiotic use and healthcare disruptions, fostering the selection and spread of resistant bacteria. Despite the clinical urgency, the genomic characterization and transmission dynamics of carbapenemase-encoding genes (CEGs) in CREC during this period have been insufficiently explored. The reference study by Chen et al. addresses this knowledge gap by analyzing CREC isolates collected from eight teaching hospitals in Guangdong Province between December 2022 and June 2024.

Key Innovation from the Reference Study

The principal innovation of this research lies in its comprehensive, multi-institutional molecular epidemiology of CREC during the COVID-19 era. Using a combination of plasmid elimination, conjugation assays, and genotyping, the study delineates not only the prevalence and genetic context of CEGs—especially blaNDM-1—but also their horizontal transfer efficiency. The work provides critical quantitative evidence on the high rate of CEG carriage on plasmids and the dominant role of mobile genetic elements like ISEcp1 in mediating resistance gene dissemination. This granular view of CEG landscape and mobility offers a robust framework for tracking and mitigating the spread of MDR pathogens in hospital settings.

Methods and Experimental Design Insights

Fifty-four non-duplicate CREC isolates were collected systematically from diverse clinical departments. The study employed variable-temperature SDS plasmid elimination and polymerase chain reaction (PCR) to map the presence and chromosomal/plasmid location of key carbapenemase genes (blaNDM-1, blaIMP, blaKPC-2). Conjugation experiments were conducted to assess the horizontal transferability of these resistance determinants. The broth microdilution method evaluated antimicrobial susceptibility profiles, while ERIC-PCR and cluster analysis using NTSYS software were used for genotyping. Additionally, mobile genetic elements were identified to elucidate the mechanisms facilitating gene transmission.

Protocol Parameters

• Sample collection: 54 CREC isolates from eight hospitals, December 2022 – June 2024.
• Plasmid elimination: Variable temperature SDS-based protocol to distinguish chromosomal versus plasmid CEGs.
• PCR detection: Targeted for blaNDM-1, blaIMP, blaKPC-2, and mobile element markers.
• Conjugation assays: Standard filter mating with recipient strains, success rate evaluated by PCR.
• Antimicrobial susceptibility: Broth microdilution for key agents (imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, levofloxacin).
• Genotyping: ERIC-PCR clustering using NTSYS software, with Dice coefficient for relatedness.

Core Findings and Why They Matter

The study revealed a high prevalence (85.19%) of CEGs among CREC isolates. Notably, blaNDM-1 was found both on plasmids and chromosomes in 33.33% of isolates and exclusively on plasmids in 46.30%, underlining the plasmid's central role in resistance gene dissemination. Minor fractions carried blaIMP (3.70%) or co-harbored blaNDM-1 and blaKPC-2 (1.85%). The CEG-positive group exhibited significantly higher resistance to multiple antimicrobials, including imipenem and cefepime (reference study), underscoring the challenge of treating these infections.

Plasmid conjugation experiments demonstrated a remarkable 95.65% success rate in CEG transfer, with nearly all blaNDM-1 genes successfully mobilized. Six types of mobile genetic elements were identified, with ISEcp1 being most prevalent (87.04%). Genotyping partitioned the isolates into 17 clusters, with two dominant types (E and G), and highlighted epidemiological risk factors: higher detection rates were observed in males, elderly patients, those in respiratory medicine, and in sputum specimens.

These findings reinforce the urgent need for robust infection control and surveillance, as the efficient horizontal transfer of CEGs, especially via plasmids, can accelerate the spread of pan-resistant strains in clinical settings.

Comparison with Existing Internal Articles

Several recent reviews and protocol-driven articles have addressed the challenges posed by multidrug-resistant Gram-negative pathogens, focusing on glycylcycline antibiotics like Tigecycline as potential solutions. For instance, the article "Tigecycline: Advanced Glycylcycline Applications in CREC Resistance Research" discusses the mechanistic rationale for deploying Tigecycline against CREC, highlighting its efficacy in both in vitro and in vivo models. This complements the current study by providing translational insight into how glycylcycline antibiotics can serve as last-resort options where carbapenem resistance is mediated by CEGs such as blaNDM-1.

Furthermore, "Tigecycline: Strategic Guidance for Translational Infection Research" integrates epidemiological findings with validated workflows, emphasizing the translational relevance of CEG surveillance and the practical implementation of Tigecycline in experimental infection models. Both internal resources echo the reference study's call for a nuanced understanding of resistance mechanisms and the importance of tailored antimicrobial strategies in research and clinical settings.

Limitations and Transferability

While the study provides a robust molecular and epidemiological snapshot, it is geographically limited to Guangdong and temporally restricted to the COVID-19 period. The sample size, though comprehensive, may not capture the full genetic diversity of CREC or the spectrum of resistance mechanisms emerging in other regions or post-pandemic contexts. Additionally, while the study elucidates the mechanisms of CEG transfer, it does not address therapeutic outcomes or the clinical efficacy of glycylcycline antibiotics in these particular settings.

Research Support Resources

For researchers seeking to model multidrug-resistant Enterobacteriaceae or validate antimicrobial agents against carbapenemase-producing strains, tools and reagents should reflect the latest resistance trends and genetic architectures. Tigecycline (SKU A5226) is widely utilized as a reference glycylcycline antibiotic in CREC infection models and MDR research. Its robust activity against both methicillin-resistant Staphylococcus aureus (MRSA) and glycopeptide-intermediate Staphylococcus aureus (GISA), as well as its proven efficacy in tissue-penetration and resistance profiling studies, make it a valuable asset for experimental workflows. Validated protocols and Tigecycline's properties, as reported in the product information, can help reproduce critical aspects of MDR bacterial research, including the investigation of novel CEG transmission dynamics.