Transmission Dynamics of Carbapenemase-Encoding Genes in Carbapenem-Resistant Enterobacter cloacae: Insights from Guangdong Province (2022–2024)

Study Background and Research Question

Carbapenem-resistant Enterobacter cloacae (CREC), a member of the Enterobacteriaceae family, has emerged as a critical contributor to global multidrug resistance, particularly in nosocomial settings. The COVID-19 pandemic has exacerbated this challenge by increasing antibiotic usage and disrupting standard infection control. Despite growing clinical concern, detailed analyses of the genetic underpinnings and transmission mechanisms of carbapenemase-encoding genes (CEGs) in CREC remain sparse. Addressing this gap, Chen et al. (2025) conducted a multicenter investigation to characterize the genetic landscape and transferability of CEGs in CREC isolates from major teaching hospitals in Guangdong, China, over an 18-month period.

Key Innovation from the Reference Study

The principal innovation of this study lies in its granular dissection of CEG carriage and dynamics, with a specific focus on the plasmid versus chromosomal localization of resistance determinants. The researchers not only documented the high prevalence of the blaNDM-1 gene but also systematically tracked the gene's mobility and association with multiple mobile genetic elements. This dual approach—combining genotypic mapping with functional transmission assays—provides a robust framework for understanding how resistance traits propagate within and between hospital populations during pandemic-related stress.

Methods and Experimental Design Insights

The study analyzed 54 non-duplicate CREC isolates collected from eight teaching hospitals between December 2022 and June 2024. The core methodological features included:

• Plasmid Elimination and PCR Typing: Variable temperature sodium dodecyl sulfate (SDS) plasmid elimination was applied, followed by PCR to detect the presence and localization of CEGs (blaNDM-1, blaIMP, and blaKPC-2).
• Antibiotic Susceptibility Testing: Broth microdilution determined resistance profiles to key agents, including imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
• Plasmid Conjugation and Transfer Efficiency: In vitro conjugation experiments measured the horizontal gene transfer rates of CEGs, supported by further PCR validation of transconjugants.
• Genotyping and Epidemiological Analysis: ERIC-PCR and NTSYS clustering categorized isolates into 17 genotypes, facilitating correlation with clinical and demographic parameters.
• Mobile Genetic Elements Mapping: The study characterized six types of mobile elements, with special attention to the prevalence and co-occurrence of ISEcp1.

This comprehensive experimental design enables direct assessment of both the genetic context and functional mobility of resistance determinants, a significant advance over studies limited to genomic surveys.

Core Findings and Why They Matter

Several critical findings emerged from the study:

• High Prevalence of CEGs: 85.19% (46/54) of CREC isolates harbored one or more CEGs, with the blaNDM-1 gene being the most frequent. Notably, 33.33% of isolates carried blaNDM-1 on both chromosomes and plasmids, while 46.30% had it exclusively on plasmids.
• Multidrug Resistance Patterns: The CEG-positive group demonstrated substantially elevated resistance rates to a spectrum of antibiotics—including levofloxacin—compared to CEG-negative counterparts (Chen et al., 2025).
• Efficient Horizontal Transfer: Plasmid conjugation experiments showed a 95.65% success rate for CEG transfer, with nearly all blaNDM-1 and all blaIMP genes being mobilized, underscoring the risk of rapid resistance dissemination.
• Mobile Genetic Element Complexity: The insertion sequence ISEcp1 was found in 87.04% of isolates, often in combination with up to three other mobile elements, reflecting a high potential for integrative mobilization of resistance genes.
• Epidemiological Hotspots: CEG-positive isolates were disproportionately recovered from male and elderly patients, respiratory medicine wards, and sputum samples, suggesting specific clinical and demographic risk profiles.

Collectively, these insights reinforce the urgent need for enhanced surveillance and targeted intervention strategies in hospital environments where plasmid-mediated resistance can quickly undermine treatment options.

Comparison with Existing Internal Articles

Recent literature on combating multidrug-resistant Gram-negative pathogens has focused on both the development of novel antibiotics and the optimization of experimental tools for resistance research. For example, the introduction of ceftolozane/tazobactam as detailed in internal reviews provides a therapeutic countermeasure for ESBL-producing Enterobacteriaceae, although its efficacy can be compromised when resistance genes are highly mobile, as observed in the Guangdong study.

On the research side, thought-leadership articles on Levofloxacin emphasize its dual role as a synthetic fluoroquinolone antibiotic targeting the bacterial DNA replication pathway and as a probe in osteoblast growth inhibition assays or chondrocyte glycosaminoglycan synthesis studies. The high resistance rates to levofloxacin reported in the CREC study highlight the growing challenge of using established antibacterial agents for both clinical and experimental purposes, necessitating careful workflow adaptation. APExBIO’s Levofloxacin is frequently cited in these contexts for its reliability in cell-based and resistance mechanism assays (workflow review).

Limitations and Transferability

While the study provides an in-depth snapshot of CEG transmission within a defined regional network during the COVID-19 era, several limitations should be noted:

• Geographic and Temporal Scope: The findings are specific to eight hospitals in Guangdong and may not fully represent dynamics in other regions or post-pandemic settings.
• Clinical Outcome Data: The study focuses on genetic and in vitro transfer parameters, with limited linkage to patient-level treatment outcomes or infection control interventions.
• Resistance Mechanism Breadth: While the analysis includes major CEGs and several mobile elements, other resistance mechanisms (e.g., efflux pumps or porin mutations) were not systematically addressed.

Nevertheless, the experimental design and genotyping protocols are transferable to other surveillance networks aiming to monitor the spread of carbapenemase genes in Enterobacteriaceae.

Protocol Parameters

• Plasmid elimination by variable temperature SDS: Apply SDS at sublethal concentrations and subject isolates to incremental temperature changes to selectively cure plasmids prior to PCR analysis of chromosomal and extrachromosomal gene presence.
• PCR detection of CEGs: Design primers targeting blaNDM-1, blaIMP, and blaKPC-2; validate specificity with positive and negative controls; use post-elimination lysates to confirm gene localization.
• Broth microdilution resistance testing: Prepare serial dilutions of antibiotics (imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, levofloxacin) and inoculate with standardized bacterial suspensions; interpret minimum inhibitory concentrations according to CLSI guidelines.
• Plasmid conjugation assays: Mix donor (CEG-positive) and recipient strains at a 1:1 ratio, incubate on non-selective media, and select transconjugants on antibiotic-containing plates; confirm gene transfer by PCR.
• ERIC-PCR genotyping: Amplify repetitive sequences using consensus primers; analyze banding patterns with NTSYS software to determine genotype clusters and epidemiological links.

Research Support Resources

For researchers investigating antibacterial resistance mechanisms or designing osteoblast growth inhibition or calcium deposition inhibition workflows, Levofloxacin (SKU B1959) from APExBIO offers a well-characterized synthetic fluoroquinolone antibiotic suitable for both bacterial DNA gyrase inhibition studies and advanced cell-based assays. The product’s detailed datasheet and storage guidelines support experimental reproducibility, particularly in resistance profiling and bone metabolism research. Researchers can find further workflow support in recent reviews on the use of Levofloxacin for DNA replication and chondrocyte glycosaminoglycan synthesis studies.