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

Study Background and Research Question

The COVID-19 pandemic has placed extraordinary pressure on healthcare systems globally, intensifying the threat posed by antimicrobial resistance. Among the most concerning pathogens are carbapenem-resistant Enterobacteriaceae (CRE), which severely limit therapeutic options. Carbapenem-resistant Enterobacter cloacae (CREC) occupies a critical niche within this group, ranking third in clinical prevalence in China after Klebsiella pneumoniae and Escherichia coli. Widespread use of antibiotics, disruption of infection control, and the complexity of COVID-19 patient management have all contributed to the increased emergence and dissemination of drug-resistant bacteria. Yet, granular understanding of the genetic mechanisms—specifically, the distribution and mobility of carbapenemase-encoding genes (CEGs)—remains limited in the context of the pandemic. The reference study addresses this gap by asking: What are the molecular characteristics and transmission dynamics of CEGs in CREC isolates collected from multiple teaching hospitals during the COVID-19 era?

Key Innovation from the Reference Study

The central innovation of the study by Chen et al. lies in its comprehensive mapping of both chromosomal and plasmid-borne CEGs—especially blaNDM-1—in a large multi-center cohort of CREC isolates drawn during a period of significant epidemiological upheaval. By combining molecular genotyping, plasmid elimination, conjugation assays, and resistance profiling, the authors elucidate not only the prevalence of key resistance determinants but also their remarkable capacity for horizontal and vertical transfer across diverse clinical settings. This integrated approach reveals the primary role of mobile genetic elements, especially ISEcp1, in facilitating the rapid dissemination of multidrug resistance during a time when healthcare infrastructures were under unusual strain.

Methods and Experimental Design Insights

The investigators collected 54 non-duplicate CREC isolates from eight teaching hospitals in Guangdong province between December 2022 and June 2024. Strain characterization involved standardized laboratory techniques:

• Plasmid elimination was achieved using variable temperature sodium dodecyl sulfate (SDS) treatments to distinguish chromosomal from plasmid-borne resistance genes.
• Polymerase chain reaction (PCR) was employed to detect the presence of blaNDM-1, blaIMP, and blaKPC-2 genes.
• Antibiotic susceptibility testing via the broth microdilution method provided quantitative resistance profiles for key antimicrobials—imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
• Conjugation experiments were conducted to assess the transferability of CEGs, simulating horizontal gene transfer events.
• Mobile genetic elements were mapped, with the prevalence of ISEcp1 and other insertion sequences characterized through molecular assays.
• ERIC-PCR and NTSYS software facilitated genotyping and cluster analysis to identify prevalent epidemiological genotypes and their distribution across hospitals and departments.

This multi-pronged design allowed the authors to link genotypic profiles with phenotypic resistance and trace the epidemiological movement of key resistance genes.

Protocol Parameters

• Sample collection window: December 2022 – June 2024; non-duplicate isolation from eight teaching hospitals.
• Plasmid elimination: Variable temperature SDS method to distinguish plasmid versus chromosomal gene carriage.
• Antibiotic susceptibility: Broth microdilution for imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, levofloxacin.
• Gene detection: PCR targeting blaNDM-1, blaIMP, blaKPC-2.
• Conjugation assay: Standard filter-mating protocol; success rates recorded for gene transfer events.
• Genotyping: ERIC-PCR with cluster analysis for epidemiological mapping.

Core Findings and Why They Matter

The study reports several notable findings:

• High prevalence of CEGs: 85.19% of isolates carried at least one carbapenemase-encoding gene, with blaNDM-1 being most prevalent.
• Plasmid predominance: 33.33% of isolates carried blaNDM-1 on both chromosome and plasmids, while 46.30% harbored it exclusively on plasmids. This supports the hypothesis that plasmid-borne resistance is especially mobile and clinically significant.
• Efficient horizontal transfer: Conjugation experiments demonstrated a 95.65% success rate in CEG transfer among CEG-positive isolates, with blaNDM-1 showing 95.45% transferability. This highlights the epidemiological risk posed by mobile resistance determinants.
• Genetic context: Six mobile genetic elements were identified, with ISEcp1 present in 87.04% of isolates. Notably, 40.74% of strains carried four types of mobile elements simultaneously, indicating a complex mosaic structure supporting gene mobility.
• Epidemiological clustering: ERIC-PCR typing grouped the 54 strains into 17 genotypes, with two (type E and G) dominating and spreading across diverse hospital departments. Sputum samples, elderly patients, and respiratory departments saw the highest rates of CEG detection.
• Resistance phenotype: CEG-positive strains were significantly more resistant than their CEG-negative counterparts to all tested antibiotics (P<0.05), underscoring the clinical challenge these strains present.

Collectively, these findings reveal that during the pandemic, CREC not only increased in prevalence but also acquired and transmitted high-risk resistance determinants with remarkable efficiency. The identification of dominant mobile elements and genotypes provides actionable targets for molecular surveillance and infection control.

Comparison with Existing Internal Articles

The current study’s emphasis on plasmid-mediated resistance and transmission dynamics aligns with broader antimicrobial research trends. For example, internal reviews of CREC in Guangdong reinforce the dominance of blaNDM-1 and highlight the urgency of tracking mobile genetic elements in hospital settings. Meanwhile, the role of advanced antimicrobials such as Tigecycline has been extensively discussed in multidrug resistance research workflows, where glycylcycline antibiotics are positioned as vital tools against organisms bearing mobile and chromosomal resistance genes. These internal resources collectively underscore the need for combinatorial approaches—genomics, surveillance, and innovative antimicrobial agents—to address the contemporary landscape of resistance.

Limitations and Transferability

As with many surveillance studies, some limitations merit consideration. The dataset, while multi-center, is geographically limited to Guangdong province and a two-year window. The absence of detailed clinical outcome data restricts direct linkage between genetic findings and patient prognosis. Furthermore, the study did not explore the full diversity of CEGs beyond the major subtypes (blaNDM-1, blaIMP, blaKPC-2), nor did it systematically investigate environmental reservoirs or transmission networks outside the hospital context. Nevertheless, the methodologies and key insights are highly transferable: the approaches described can be readily adapted to similar settings facing outbreaks of multidrug-resistant Enterobacteriaceae, particularly where molecular surveillance and targeted infection control are priorities.

Research Support Resources

For laboratories investigating multidrug resistance, especially as it relates to the genetic mobility of resistance determinants, robust experimental tools remain essential. Glycylcycline antibiotics such as Tigecycline (SKU A5226) provide a validated option for in vitro and in vivo studies targeting multidrug-resistant bacteria, including carbapenem-resistant and glycopeptide-intermediate strains. As detailed in recent workflow guides, Tigecycline’s mechanism as a 30S ribosomal subunit inhibitor and its broad-spectrum activity can be leveraged in both genetic and phenotypic assays. Researchers can consult APExBIO for technical specifications and recommended protocols to optimize their resistance characterization experiments and model the efficacy of next-generation antimicrobial agents.