Transmission Dynamics of Carbapenemase Genes in CREC During COVID-19

Study Background and Research Question

Carbapenem-resistant Enterobacter cloacae (CREC) represents one of the most pressing challenges in antimicrobial resistance, ranking just behind Klebsiella pneumoniae and Escherichia coli in prevalence among carbapenem-resistant Enterobacteriaceae in China. The COVID-19 pandemic, with its increased antibiotic utilization and healthcare disruptions, has further complicated resistance epidemiology. However, granular investigations into the molecular characteristics and transmission dynamics of carbapenemase-encoding genes (CEGs) in CREC, especially during the pandemic period, have been limited. The reference study by Chen et al. (BMC Microbiology 2025) addresses this knowledge gap by systematically analyzing 54 CREC isolates collected from eight teaching hospitals in Guangdong Province between December 2022 and June 2024.

Key Innovation from the Reference Study

The central innovation of Chen et al.'s work lies in its comprehensive characterization of CEG carriage, localization (plasmid vs. chromosomal), and transferability in a real-world clinical setting during an unprecedented global health crisis. Employing robust molecular and phenotypic methodologies, the study elucidates not only the prevalence but also the mechanisms underlying horizontal and vertical dissemination of major CEGs, especially the blaNDM-1 gene. The research further integrates genotypic profiling and epidemiological data to map the spread and clustering of resistance determinants within and across hospital environments.

Methods and Experimental Design Insights

To dissect the genetic and phenotypic landscape of carbapenem resistance in CREC, the study utilized several complementary approaches:

• Collection of 54 non-redundant CREC isolates from eight geographically distributed tertiary hospitals.
• Detection and localization of CEGs via PCR, with particular focus on the blaNDM-1, blaIMP, and blaKPC-2 genes.
• Plasmid elimination using variable temperature Sodium Dodecyl Sulfate (SDS) treatment, enabling distinction between chromosomal and plasmid-borne resistance genes.
• Phenotypic resistance profiling by the broth microdilution method, comparing CEG-positive and CEG-negative CREC isolates.
• Plasmid conjugation assays to assess transferability of resistance determinants, followed by PCR confirmation in recipient strains.
• Genotyping by ERIC-PCR and clustering with NTSYS software to investigate strain diversity and epidemiological relationships.
• Analysis of mobile genetic elements (MGEs) associated with CEGs, focusing on insertion sequences such as ISEcp1.

Protocol Parameters

• Plasmid elimination: Variable temperature SDS treatment was employed to distinguish CEG localization; optimization of SDS concentration and incubation conditions is critical for efficiency (reference study).
• Plasmid conjugation: Mating experiments conducted at 37°C for 18–24 hours, with recipient strains selected on appropriate antibiotic-containing media.
• Broth microdilution: Antimicrobial susceptibility testing followed CLSI guidelines, using a defined panel of antibiotics relevant to clinical management and resistance surveillance.
• Genotyping: ERIC-PCR profiles analyzed with NTSYS-pc software, grouping strains based on Dice similarity coefficients.

Core Findings and Why They Matter

The reference study found a remarkably high prevalence of CEGs among CREC isolates: 85.19% (46/54) carried carbapenemase genes, with blaNDM-1 being the most frequent. Notably, 33.33% of isolates harbored blaNDM-1 on both chromosome and plasmid, while 46.30% carried it exclusively on plasmids. The presence of CEGs correlated with significantly elevated resistance rates to key antibiotics, including imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin (P < 0.05), underlining the clinical impact of CEG dissemination.

Plasmid conjugation experiments demonstrated a 95.65% overall success rate for CEG transfer, with blaNDM-1 and blaIMP exhibiting particularly high mobility. This underscores the threat posed by plasmid-mediated horizontal gene transfer in facilitating rapid spread of multidrug resistance. The study also mapped six types of mobile genetic elements, with ISEcp1 detected in 87.04% of isolates—suggesting a key role for this insertion sequence in gene mobilization.

Genotypic analysis identified 17 CREC genotypes, with type E and G being most prevalent and widely distributed across hospital departments. Epidemiological breakdown revealed highest CEG detection in male and elderly patients, within respiratory medicine, and in sputum samples—a profile consistent with high-risk populations and transmission settings during the pandemic (Chen et al.).

Comparison with Existing Internal Articles

Several internal reviews and protocol-focused articles expand on the molecular biology tools and workflows relevant to CEG research. For instance, "Chloramphenicol in Plasmid Selection: Protocols & Innovations" contextualizes the use of chloramphenicol—also known as 2,2-dichloro-N-[(1R,2R)-1,3-dihydroxy-1-(4-nitrophenyl)propan-2-yl]acetamide—as a high-stringency selection agent in resistance gene transfer studies. The internal review "Chloramphenicol in Translational Research" further details how robust selection systems using this bacterial protein synthesis inhibitor enable reliable tracking of plasmid-encoded resistance determinants, supporting mechanistic studies similar to those described in the reference paper.

These resources highlight best practices for plasmid selection assays and underscore the relevance of high-purity chloramphenicol for reproducible molecular biology research, particularly when investigating the mobility and stability of resistance elements in Enterobacteriaceae.

Limitations and Transferability

While the reference study provides a rigorous, multi-institutional snapshot of CEG epidemiology during the COVID-19 pandemic, certain limitations warrant consideration. The analysis is geographically confined to Guangdong Province and temporally bounded to the pandemic period, which may limit generalizability to other regions or non-pandemic contexts. The sample size, though robust for molecular profiling, may not capture all circulating genotypes or rare resistance mechanisms. Additionally, while plasmid transfer was highly efficient in vitro, in vivo dynamics may be modulated by environmental, host, or microbial factors not fully replicated in laboratory conditions.

Nonetheless, the methodological framework—combining molecular detection, plasmid elimination, and conjugation assays—offers a transferable template for resistance gene surveillance in diverse hospital environments. Protocols and findings may inform infection control strategies and guide further research into the containment of multidrug-resistant Enterobacteriaceae.

Research Support Resources

To enable similar workflows, researchers can employ Chloramphenicol (SKU A2512), a well-characterized antimicrobial agent and inhibitor of bacterial 50S ribosomal subunit, for stringent plasmid selection or molecular biology applications. The compound’s mode of action and specifications (product information) support high-fidelity selection of resistance markers in Enterobacteriaceae and related genetic studies. For detailed protocol recommendations and troubleshooting, see the internal article "Chloramphenicol in Molecular Biology: Plasmid Assays & Beyond". As always, laboratory implementation should adhere to biosafety and regulatory standards, especially when handling multidrug-resistant organisms or resistance gene constructs.