Genomic Characterization and Transmission of Carbapenemase Genes in CREC

Study Background and Research Question

Carbapenem-resistant Enterobacter cloacae (CREC) is emerging as a critical challenge in hospital settings, especially as the frequency of multidrug-resistant Gram-negative infections continues to rise globally. The COVID-19 pandemic has compounded this risk, increasing selective pressures through heightened antibiotic use and disruption of routine infection control. In this context, the recent multicenter study by Chen et al. (BMC Microbiology, 2025) addresses a pressing research question: What are the prevalence, genetic context, and transmission dynamics of carbapenemase-encoding genes (CEGs) in CREC isolates collected from teaching hospitals in Guangdong, China during 2022–2024?

Key Innovation from the Reference Study

The primary innovation of the Chen et al. study lies in its comprehensive molecular and epidemiological dissection of CEGs within a real-world, multicenter hospital network during a period of exceptional antimicrobial pressure. Notably, the research systematically distinguishes between chromosomal and plasmid-borne resistance determinants, with a focus on the blaNDM-1 gene, and quantifies their transferability in vitro. The study also applies high-resolution genotyping to characterize clonal relationships, providing a detailed map of both horizontal and vertical gene transfer events in CREC populations.

Methods and Experimental Design Insights

The investigators analyzed 54 non-duplicate CREC clinical isolates obtained from eight teaching hospitals between December 2022 and June 2024. They employed PCR and the variable temperature SDS plasmid elimination technique to determine the presence, location (chromosome vs. plasmid), and transmissibility of CEGs. Resistance profiles were established via broth microdilution, while ERIC-PCR and NTSYS software enabled genotypic clustering. Plasmid conjugation assays assessed inter-strain gene transfer capabilities, and mobile genetic elements were identified to elucidate mechanisms of gene dissemination.

Protocol Parameters

• Plasmid elimination: Use variable temperature SDS treatment to distinguish plasmid-borne from chromosomal CEGs in Enterobacteriaceae.
• Antibiotic susceptibility testing: Perform broth microdilution to determine MICs for imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
• Genotyping: Apply ERIC-PCR with analysis in NTSYS for strain clustering by Dice coefficient.
• Plasmid conjugation assay: Use filter mating or broth mating protocols to evaluate CEG transfer between donor and recipient strains, confirming transfer via PCR.

Core Findings and Why They Matter

According to the reference study, 85.19% of CREC isolates harbored CEGs, with blaNDM-1 being predominant. Specifically, 33.33% of isolates carried blaNDM-1 on both chromosomes and plasmids, while 46.30% had it exclusively on plasmids. The presence of blaIMP and blaKPC-2 was less frequent. Notably, the CEG-positive group exhibited significantly higher resistance rates to multiple antibiotics compared to the CEG-negative group (P < 0.05), underscoring the clinical challenge posed by multidrug-resistant CREC.

The study demonstrated efficient horizontal transfer of CEGs via plasmid conjugation, with a 95.65% success rate; blaNDM-1 and blaIMP transferred readily, whereas blaKPC-2 did not. Mobile genetic element analysis revealed that ISEcp1 was the most prevalent, present in 87.04% of isolates, and that co-occurrence of multiple elements was common. Genotypic analysis clustered the isolates into 17 types, with two (E and G) accounting for over 40% of the strains. Epidemiologically, detection rates were highest in male and elderly patients, respiratory medicine wards, and sputum samples.

These findings highlight the dual risks of clonal spread and mobile genetic element-mediated horizontal gene transfer in facilitating the persistence and dissemination of high-risk resistance determinants. The predominance of plasmid-driven blaNDM-1 transfer is particularly concerning for infection control and therapeutic decision-making, given the paucity of effective antibiotics for such strains.

Comparison with Existing Internal Articles

The internal review "Carbapenemase Genes in Enterobacter cloacae: Transmission and Resistance Insights" supports the external findings by mapping the high prevalence and genetic mobility of blaNDM-1 in regional isolates, thus corroborating the reference study's assertion that plasmid-mediated resistance is a dominant mechanism in these settings. Furthermore, protocol-focused resources such as "Aztreonam: Applied Workflows for Gram-Negative Resistance Assays" and "Aztreonam: Optimizing Monocyclic β-Lactam Antibiotic Workflows" discuss how monocyclic β-lactam antibiotics, including Aztreonam, can be integrated into experimental designs that probe resistance mechanisms and phenotypes, especially in the context of multidrug-resistant Gram-negative bacteria.

Limitations and Transferability

While the multicenter design and molecular depth of the study enhance its generalizability within Guangdong Province, some limitations remain. The sample size, though representative, is relatively small for extrapolation to other geographic regions or to community-acquired CREC. The focus on hospitalized cases may bias the detection of certain genotypes or resistance patterns prevalent in nosocomial settings. Additionally, while in vitro conjugation assays demonstrate the potential for horizontal gene transfer, they may overestimate transfer rates compared to in vivo conditions. The study’s findings are nonetheless directly transferable to hospital epidemiology surveillance and resistance mechanism research, especially in regions facing similar antimicrobial pressures.

Research Support Resources

To facilitate further research into antibiotic activity against Gram-negative aerobic bacteria and resistance mechanisms, investigators may leverage Aztreonam (SKU A5931), a fully synthetic monocyclic β-lactam antibiotic. Aztreonam’s well-characterized solubility in water and DMSO, along with its specific inhibition of bacterial cell wall synthesis, makes it a robust tool for validating resistance phenotypes and studying the impact of β-lactamase production in Enterobacteriaceae. As highlighted in internal workflow guides, Aztreonam can also be used to examine bone marrow progenitor cell inhibition and effects on hepatic cytochrome P450 enzymes in experimental systems. For detailed protocols and product specifications, APExBIO provides comprehensive support for research use only applications.