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

Study Background and Research Question

Carbapenem-resistant Enterobacteriaceae (CRE) represent a growing public health concern, with Enterobacter cloacae (CREC) ranked as the third most frequently detected carbapenem-resistant species in China. The COVID-19 pandemic has further complicated resistance patterns due to increased antibiotic usage, healthcare service interruptions, and challenging patient management, fostering the emergence and spread of multidrug-resistant bacteria. Despite these trends, systematic molecular investigations into the distribution, mechanism, and transmission of carbapenemase-encoding genes (CEGs) in CREC remain limited, especially in the context of pandemic-related healthcare dynamics. The recent study by Chen et al. (2025) addresses this gap by analyzing the prevalence, genetic context, and transmissibility of CEGs in CREC isolates from multiple tertiary hospitals in Guangdong Province.

Key Innovation from the Reference Study

The principal innovation of this study lies in its comprehensive molecular and epidemiological profiling of 54 CREC isolates collected between December 2022 and June 2024 across eight hospitals. By integrating variable temperature SDS plasmid curing, PCR-based gene detection, plasmid conjugation, and ERIC-PCR-based genotyping, the researchers provide an unusually detailed landscape of CEG diversity, chromosomal versus plasmid localization, and real-world transmission potential. Notably, the research highlights the dominance of the blaNDM-1 gene—frequently found on plasmids—and demonstrates high rates of successful horizontal gene transfer, which together underpin the rapid spread of multidrug resistance in clinical settings.

Methods and Experimental Design Insights

Chen et al. utilized a robust suite of molecular tools to dissect the genetic architecture and mobility of carbapenemase genes within CREC. The main experimental components included:

• Sample Collection: Fifty-four non-duplicate CREC isolates were obtained from eight teaching hospitals across Guangdong Province, representing a wide clinical and demographic spectrum.
• Plasmid and Chromosomal Localization: Variable temperature SDS plasmid elimination was combined with targeted PCR to discriminate between chromosomal and plasmid-borne CEGs.
• Antibiotic Susceptibility Testing: The broth microdilution method determined resistance profiles against a panel of antibiotics, stratified by CEG status.
• Conjugation Experiments: Plasmid transfer efficiency was assessed via filter mating, followed by PCR confirmation of gene transfer.
• Mobile Genetic Element (MGE) Profiling: Six MGEs, including ISEcp1, were identified and quantified in each isolate.
• Genotyping: ERIC-PCR and NTSYS software enabled high-resolution discrimination among the 54 isolates, identifying 17 genotypes and mapping their epidemiological distribution.

Protocol Parameters

• Variable temperature SDS plasmid elimination: Used to differentiate chromosomal versus plasmid-encoded genes; typically involves culturing isolates with SDS at elevated temperatures for several generations.
• Broth microdilution for MIC determination: Standardized concentrations of antibiotics, with CEG-positive and -negative groups compared using P-value thresholds (P < 0.05 for significance).
• Conjugation assays (filter mating): Donor and recipient strains mixed on membrane filters, incubated, and transconjugants selected on antibiotic media for PCR validation.
• ERIC-PCR: Genotyping performed according to established protocols, with cluster analysis using Dice coefficients and NTSYS software.

Core Findings and Why They Matter

The study reveals several critical findings that have major implications for infection control and antimicrobial stewardship:

• High Prevalence of CEGs: 85.19% of CREC isolates (46/54) harbored at least one carbapenemase-encoding gene, predominantly blaNDM-1.
• Plasmid Dominance: blaNDM-1 was located on both plasmids and chromosomes in 33.33% of isolates, but exclusively on plasmids in 46.30%, highlighting the central role of mobile genetic elements in resistance dissemination.
• Efficient Horizontal Transfer: Conjugation experiments showed a remarkable 95.65% (44/46) success rate for gene transfer, with blaNDM-1 and blaIMP transferring at >95% efficiency, underscoring the real-world risk of rapid resistance spread.
• Multidrug Resistance Phenotype: CEG-positive strains displayed significantly higher resistance rates to imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin compared to CEG-negative strains (P < 0.05).
• Genotype and Epidemiology: ERIC-PCR differentiated 17 genotypes, with types E and G most prevalent. CEGs were found more frequently in isolates from male and elderly patients, respiratory medicine settings, and sputum samples.
• MGE Complexity: ISEcp1 was the most prevalent MGE (87.04%), and 40.74% of isolates carried four types of MGEs simultaneously, facilitating complex gene mobilization events.

Together, these findings demonstrate that not only are CEGs widespread in CREC, but they are also highly mobile and associated with multidrug resistance, intensifying clinical management challenges.

Comparison with Existing Internal Articles

Insights from the reference study align with and extend the themes explored in several recent reviews of glycylcycline antibiotics. For example, "Tigecycline’s Translational Edge" contextualizes the growing threat of multidrug-resistant (MDR) pathogens like CREC and the translational importance of glycylcycline antibiotics as last-resort options. Similarly, "Tigecycline: A Glycylcycline Antibiotic for Multidrug-Resistant Bacteria" details how tigecycline, a 30S ribosomal subunit inhibitor, provides robust activity against organisms harboring resistance determinants akin to those described in the Chen et al. study. The current research deepens our understanding of the genetic context—particularly the plasmid-mediated spread—underpinning the rise of resistance phenotypes that challenge even advanced antimicrobials.

Furthermore, articles such as "Tigecycline in the Genomics Era" discuss the application of tigecycline in research settings focused on multidrug-resistant bacteria, echoing the urgent need for new agents and strategies in light of the rapid gene transfer mechanisms documented by Chen et al.

Limitations and Transferability

While this study offers a comprehensive snapshot of resistance gene dynamics during a period of heightened clinical stress, several limitations should be noted:

• Regional Focus: Findings are based on isolates from one province, which may limit direct generalizability to other geographic or epidemiological settings.
• Short Surveillance Window: The study covers an 18-month period; long-term trends require ongoing surveillance.
• Clinical Correlation: The work focuses on molecular and phenotypic profiles, but does not directly link genotypes to patient outcomes or treatment responses.

Nonetheless, the core observation—robust plasmid-mediated dissemination of CEGs in clinical CREC—likely applies to similar hospital environments globally, especially under pandemic-induced pressures.

Research Support Resources

Given the high prevalence of multidrug resistance mediated by mobile carbapenemase genes, researchers investigating antimicrobial agents for multidrug-resistant bacteria or developing infection models (e.g., for glycopeptide-intermediate Staphylococcus aureus or CREC) require robust and well-characterized compounds. Tigecycline (SKU A5226) from APExBIO is a first-in-class glycylcycline antibiotic with potent in vitro and in vivo activity against a wide range of resistant pathogens, including those with complex resistance genotypes. Its documented efficacy in treatment of complicated skin and skin-structure infections, as well as validated performance in murine models of MDR infection, supports its use in translational and mechanistic studies. For detailed protocol suggestions and storage guidance, consult the product dossier.