Carbapenemase Gene Transmission in CREC During COVID-19: Insights from Guangdong Hospitals

Study Background and Research Question

Antimicrobial resistance (AMR) in Gram-negative bacteria, particularly carbapenem-resistant Enterobacter cloacae (CREC), poses a significant threat to global public health. The COVID-19 pandemic exacerbated these challenges through increased antibiotic usage and disrupted healthcare workflows, potentially accelerating the emergence and transmission of multidrug-resistant organisms. Despite the clinical urgency, detailed molecular characterization of carbapenemase-encoding genes (CEGs) and their transmission dynamics in CREC across diverse hospital settings remains limited. The reference study set out to address this gap by analyzing CREC isolates from eight teaching hospitals in Guangdong Province, China, collected between December 2022 and June 2024, with a focus on mapping CEG prevalence, genetic mobility, and epidemiological risk factors.

Key Innovation from the Reference Study

The primary innovation of this work lies in its systematic approach to characterizing both the prevalence and the transmission potential of key carbapenemase genes—most notably bla_NDM-1—across clinical and genetic contexts. By integrating plasmid elimination, PCR-based genotyping, broth microdilution resistance profiling, and mobile genetic element analysis, the study delivers a granular view of how CEGs persist and spread within hospital environments. This dual focus on horizontal and vertical gene transfer, combined with detailed epidemiological mapping, distinguishes the study from prior regional or single-hospital reports, providing essential data for the design of future antimicrobial resistance research and intervention strategies.

Methods and Experimental Design Insights

The research team employed a multi-layered protocol to dissect the molecular and epidemiological landscape of CREC:

• Sample Collection: 54 non-duplicate CREC isolates were obtained from patient specimens across eight tertiary teaching hospitals in Guangdong.
• Genetic Characterization: The presence and chromosomal/plasmid localization of CEGs (notably bla_NDM-1, bla_IMP, and bla_KPC-2) were determined using PCR after variable temperature SDS-mediated plasmid elimination.
• Antimicrobial Susceptibility Testing: Broth microdilution was used to assess resistance profiles, focusing on clinically relevant agents such as imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
• Plasmid Conjugation Experiments: The transferability of CEGs was confirmed by conjugation assays, followed by PCR in transconjugants.
• Mobile Genetic Element Typing: Six mobile genetic element types were identified by PCR, with ISEcp1 being the most prevalent.
• Genotyping and Epidemiology: ERIC-PCR and NTSYS software were used to categorize strains into molecular genotypes, and patient/departmental epidemiological data were integrated to identify risk factors.

Protocol Parameters

• Sample sourcing: Isolate CREC strains from diverse clinical departments and specimen types to capture epidemiological breadth.
• Plasmid elimination: Employ variable temperature SDS protocol for distinguishing chromosomal vs. plasmid gene localization.
• Conjugation assay setup: Validate horizontal transfer using recipient E. coli strains and select for carbapenem resistance.
• Mobile element screening: Use targeted PCR primers for known insertion sequences (e.g., ISEcp1) implicated in resistance gene mobility.
• Multilocus typing: Apply ERIC-PCR for genotypic clustering and use appropriate software (e.g., NTSYS) for similarity analysis.

Core Findings and Why They Matter

The study revealed several crucial findings with direct implications for antimicrobial resistance surveillance and research:

• CEG Prevalence: 85.19% of CREC isolates harbored carbapenemase-encoding genes, with bla_NDM-1 being the predominant determinant—present on both chromosomes and plasmids in one-third of isolates, and exclusively on plasmids in nearly half.
• Resistance Profiles: CEG-positive isolates showed significantly higher resistance to multiple antibiotic classes (including cephalosporins and fluoroquinolones) than CEG-negative strains, highlighting the multidrug-resistant phenotype driven by these genes.
• Gene Transferability: Conjugation assays demonstrated a high success rate (95.65%) for CEG transfer, particularly for bla_NDM-1 and bla_IMP, supporting the role of plasmids and mobile elements in horizontal gene spread.
• Mobile Genetic Context: ISEcp1 was the most prevalent mobile element, often co-occurring with other elements and facilitating the assemblage of complex resistance loci.
• Epidemiological Risk Factors: CEG-positive CREC were disproportionately detected in male and elderly patients, respiratory departments, and sputum samples, suggesting targeted surveillance priorities.
• Genotypic Diversity: Seventeen genotypes were identified, with two (type E and G) being most prevalent and widely distributed across hospitals and departments, indicating possible inter-facility transmission routes.

Together, these findings reinforce the need for robust infection control and molecular surveillance measures, as the rapid and efficient dissemination of CEGs, driven by both chromosomal integration and plasmid mobility, threatens to undermine the efficacy of last-resort antibiotics in hospital settings.

Comparison with Existing Internal Articles

Several internal reviews and protocol-focused articles complement the current study's findings and contextualize them for translational AMR research:

• The internal summary of carbapenemase gene dynamics in CREC corroborates the regional prevalence of bla_NDM-1 and emphasizes the importance of surveillance during pandemic periods, aligning closely with the new reference data.
• Protocol articles such as 'Cefotaxime in Translational AMR Research' and 'Cefotaxime in Antimicrobial Resistance Models' provide practical guidance on how third-generation cephalosporin antibiotics can be leveraged to build infection models and dissect resistance mechanisms, with a focus on both Gram-positive and Gram-negative pathogens. These resources bridge the molecular insights of gene transmission to actionable experimental workflows.
• Mechanistic reviews such as 'Cefotaxime: Mechanistic Depth and Strategy in AMR Research' extend the discussion to experimental design, highlighting how the findings from molecular epidemiology studies can inform the choice of antibiotics and model systems in resistance research.

Collectively, the internal articles reinforce the practical value of integrating molecular surveillance data with translational research protocols, particularly in the face of evolving multidrug resistance.

Limitations and Transferability

While this study presents robust molecular and epidemiological data, several limitations warrant consideration:

• Regional Focus: The analysis is restricted to eight teaching hospitals in Guangdong, which may limit direct generalizability to other geographic regions or less-resourced healthcare settings.
• Temporal Scope: The study captures a snapshot during the COVID-19 pandemic, and resistance dynamics may shift post-pandemic as antibiotic stewardship practices evolve.
• Genetic Resolution: Although ERIC-PCR provides valuable genotypic clustering, higher-resolution whole-genome sequencing could further elucidate transmission networks and resistance gene evolution.
• Clinical Correlation: The research is primarily focused on molecular epidemiology and does not directly address treatment outcomes or clinical management strategies.

Despite these limitations, the core findings are highly transferable to the design of antimicrobial resistance research protocols, particularly those involving third-generation cephalosporin antibiotics and bacterial infection models.

Research Support Resources

Researchers aiming to model beta-lactam antibiotic mechanisms, investigate mobile genetic element dynamics, or build clinically relevant infection models can benefit from the study's detailed methodology and surveillance data. For experimental needs, Cefotaxime (SKU BA1012) is a widely used third-generation cephalosporin antibiotic with robust activity against both Gram-positive and Gram-negative bacteria. APExBIO supplies Cefotaxime for research purposes, supporting workflows that require lactamase-resistant cephalosporins in antimicrobial resistance research and bacterial infection modeling. Researchers are advised to consult product guidelines for storage and solution preparation to maintain experimental reproducibility.