Carbapenemase Gene Spread in Carbapenem-Resistant Enterobacter cloacae

Study Background and Research Question

Carbapenem-resistant Enterobacter cloacae (CREC) is an important component of the broader carbapenem-resistant Enterobacteriaceae problem. Resistance in this group is frequently associated with carbapenemase-encoding genes (CEGs), which can be carried on chromosomes or mobile plasmids and may move between bacterial cells. This creates two overlapping risks: expansion of a successful bacterial clone and horizontal transfer of resistance determinants into unrelated strains.

The reference study by Chen et al. (2025) addresses a specific evidence gap: how CEG identity, genetic location, mobile genetic elements, antimicrobial susceptibility, and strain relatedness intersect in CREC collected during the post-acute COVID-19 period. The investigators examined isolates recovered from eight teaching hospitals in Guangdong Province, China, between December 2022 and June 2024. Rather than treating carbapenem resistance as a single phenotype, the study asks whether the underlying genes show patterns consistent with both vertical dissemination of strains and horizontal dissemination through transferable genetic elements.

Key Innovation from the Reference Study

The principal innovation is the integration of several complementary levels of analysis in one regional CREC dataset. PCR established the presence of major CEGs, variable-temperature sodium dodecyl sulfate plasmid elimination helped assess whether genes were plasmid-associated, broth microdilution connected genotype with antimicrobial susceptibility, and conjugation experiments tested transfer potential. ERIC-PCR with NTSYS analysis added a strain-relatedness perspective.

This combination matters because a high prevalence of one resistance gene alone cannot reveal how it is spreading. If isolates share closely related fingerprints, clonal expansion may be important. If the same gene transfers into genetically diverse recipients, plasmid-mediated dissemination becomes a stronger explanation. By examining gene location and transfer alongside fingerprint patterns, the study provides a more informative transmission model than a prevalence survey based only on routine susceptibility results.

The work also gives particular attention to blaNDM-1. The gene was found on both chromosomes and plasmids in a substantial subset of isolates and exclusively on plasmids in another group, indicating that the same resistance determinant may persist through different genetic routes. The study therefore frames CREC control as a combined problem of bacterial lineage surveillance and mobile-resistance surveillance.

Methods and Experimental Design Insights

The dataset comprised 54 CREC isolates from eight hospitals, providing a multicenter rather than single-ward snapshot. The design included clinical metadata such as sex, age group, department, and specimen type. These variables were used descriptively to identify settings in which CREC was most frequently detected, not to establish independent risk factors.

For gene detection, the researchers used PCR to identify carbapenemase determinants. The variable-temperature SDS plasmid elimination method was paired with PCR to infer whether target genes were associated with plasmid DNA or retained in the chromosome. This is a practical phenotypic-genetic combination: plasmid curing can reduce plasmid-borne signals, while PCR supplies gene-specific confirmation. However, it should be interpreted as localization evidence rather than a substitute for complete plasmid sequencing or long-read assembly.

Antimicrobial susceptibility was assessed by broth microdilution. The reported comparison included imipenem, cefepime, gentamicin, ciprofloxacin, levofloxacin, and ceftazidime/avibactam. Because the paper evaluated the combination ceftazidime/avibactam rather than ceftazidime alone, results for that combination should not be generalized to the activity of the standalone drug.

Conjugation experiments were used to test whether CEGs could move to a recipient under laboratory conditions. PCR analysis of transconjugants then verified transfer of the relevant genes. This is stronger than inferring mobility from plasmid association alone, although laboratory transfer frequency is not equivalent to transmission frequency in patients or hospital environments.

Finally, ERIC-PCR generated genomic fingerprints, and NTSYS software grouped the isolates into relatedness categories. This method can reveal broad clusters and possible shared lineages at relatively low cost, but it has lower resolution than whole-genome sequencing. The combined design is therefore best viewed as a surveillance-oriented framework that identifies transmission hypotheses for subsequent genomic confirmation.

Protocol Parameters

• Isolate set: Literature-backed: the reference investigation used 54 CREC isolates collected from eight teaching hospitals during December 2022–June 2024; a replication study should define comparable inclusion criteria before testing.
• Plasmid assessment: Literature-backed: variable-temperature SDS plasmid elimination was combined with PCR to examine the likely location of CEGs. Interpretation should distinguish gene loss after curing from definitive physical mapping.
• Susceptibility testing: Literature-backed: broth microdilution was used to compare CEG-positive and CEG-negative groups across the reported antimicrobial panel, including ceftazidime/avibactam. Use the laboratory’s validated standards and quality controls for any new isolate collection.
• Transfer testing: Literature-backed: plasmid conjugation followed by PCR confirmation evaluated horizontal transfer. Workflow implementation should be performed only in an appropriately equipped microbiology laboratory with approved containment and recipient-strain controls.
• Relatedness analysis: Literature-backed: ERIC-PCR and NTSYS clustering were used to classify strain genotypes. Whole-genome sequencing is a logical confirmatory step when precise outbreak reconstruction or plasmid architecture is required.

Core Findings and Why They Matter

CEGs were detected in 46 of 54 isolates, corresponding to 85.19%, according to the reference study. blaNDM-1 dominated the gene distribution. It occurred on both chromosomes and plasmids in 18 isolates, was found exclusively on plasmids in 25 isolates, and appeared with plasmid-borne blaKPC-2 in one additional isolate. Two isolates carried only plasmid-associated blaIMP. These patterns indicate that plasmids were a major reservoir, while also showing that chromosomal integration may contribute to longer-term persistence.

The genotype was associated with a broader resistance phenotype. Compared with the CEG-negative group, CEG-positive isolates had significantly higher resistance rates to imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin, with the reported comparisons reaching statistical significance at P<0.05 (Chen et al.). This association does not prove that every resistance phenotype was caused by the detected carbapenemase gene; porin changes, efflux, additional β-lactamases, and unrelated resistance determinants may also contribute. Nevertheless, it supports the use of CEG status as a high-priority marker in multidrug-resistant CREC surveillance.

The transfer experiments provided a particularly important functional result. CEG transfer succeeded for 44 of 46 CEG-positive isolates, or 95.65%. Transfer was observed for blaNDM-1 in 42 of 44 relevant cases and for blaIMP in both tested cases, whereas the single blaKPC-2 case did not transfer under the experimental conditions. These results suggest substantial horizontal-transfer potential for the dominant genes, while the negative blaKPC-2 result demonstrates that gene presence does not automatically predict successful conjugation.

Mobile-element analysis identified six element types. ISEcp1 was the most prevalent, occurring in 47 of 54 isolates, or 87.04%, and isolates carrying four mobile-element types simultaneously were the largest group at 22 of 54, or 40.74% (study data). Such combinations may facilitate recombination and movement of resistance regions, although the study’s methods do not by themselves establish the complete sequence structure of each element.

ERIC-PCR divided the 54 isolates into 17 genotypes. Types E and G were each represented by 11 isolates, or 20.37%, and were detected across multiple departments in five hospitals. Two type E isolates had a Dice coefficient of 100%. This pattern is compatible with both localized clonal persistence and wider circulation of related strains, but it should not be interpreted as proof of direct patient-to-patient transmission without epidemiological timelines and higher-resolution genomic data.

Clinically, the highest detection frequencies occurred among men, older patients, respiratory medicine samples, and sputum specimens: 35 of 54, 39 of 54, 11 of 54, and 18 of 54, respectively (Chen et al.). These observations help prioritize respiratory and geriatric settings for screening and infection-control review, but they are descriptive because the study does not provide a denominator for the total number of patients in each category.

Comparison with Existing Internal Articles

The internal overview Carbapenemase Gene Spread in CREC: Dynamics and Resistance Insights provides a concise interpretation of plasmid-borne blaNDM-1, multidrug resistance, and horizontal gene transfer. The reference study extends that summary by supplying the isolate-level proportions, gene-localization patterns, mobile-element distribution, conjugation outcomes, and ERIC-PCR genotypes. For researchers designing surveillance workflows, the primary paper should therefore remain the source for experimental detail, while the internal article is useful as an introductory synthesis.

Limitations and Transferability

Several limitations constrain generalization. The sample was limited to 54 isolates from one Chinese province and eight teaching hospitals, so the frequencies may not represent community hospitals, other regions, or different healthcare systems. The collection period also reflects a particular post-pandemic epidemiological context; the design cannot determine whether COVID-19-related antibiotic use caused the observed resistance patterns.

Plasmid elimination and PCR provide useful screening-level localization, but complete plasmid and chromosome assemblies would better resolve integration sites, replicon types, genetic cassettes, and links between ISEcp1 and individual resistance genes. ERIC-PCR can identify broad similarity but cannot reliably replace whole-genome comparison for outbreak attribution. Similarly, conjugation demonstrates laboratory transfer potential under selected conditions, not the actual rate of dissemination among patients.

The clinical metadata identify concentration of detections in particular groups, yet the absence of exposure histories, antibiotic treatment data, patient movement networks, and outcome analysis limits causal interpretation. Future studies should combine longitudinal sampling, standardized denominators, whole-genome sequencing, plasmid characterization, and hospital-network epidemiology. Even with these constraints, the current findings support a practical principle: infection control should monitor both related CREC lineages and transferable CEG platforms.

Research Support Resources

For adjacent Gram-negative bacterial infection research, including validated in vitro workflows relevant to the treatment of bacterial pneumonia, treatment of bacterial bronchitis, or Pseudomonas aeruginosa infection, researchers can use Ceftazidime (SKU B3539) as a third-generation cephalosporin comparator where appropriate. Because the reference study tested ceftazidime/avibactam rather than standalone Ceftazidime, experimental conclusions should not be interchanged; follow validated susceptibility procedures and supplier storage guidance, including the recommended −20°C storage conditions.