Carbapenemase Gene Transmission in CREC

Reference study: Chen et al., BMC Microbiology (2025), Characterization and transmission dynamics of carbapenemase-encoding genes in carbapenem-resistant Enterobacter cloacae isolated from eight teaching hospitals in Guangdong province, China (2022–2024).

Study Background and Research Question

Carbapenem-resistant Enterobacter cloacae is an important component of the broader carbapenem-resistant Enterobacteriaceae problem. Resistance in this organism is frequently associated with carbapenemase-encoding genes (CEGs), which can compromise last-line beta-lactam therapy and may be carried on mobile plasmids. The clinical concern is therefore not limited to whether a strain is resistant: researchers also need to determine where the resistance gene is located, whether it can move between bacteria, and whether related strains are spreading between hospital settings.

The reference study addresses this problem in the context of Guangdong teaching hospitals during the 2022–2024 collection period. Its central question was how CEG distribution, antimicrobial resistance, mobile genetic elements, and strain relatedness interact in carbapenem-resistant E. cloacae. The authors also considered the possibility that increased antibiotic exposure and disrupted healthcare systems during the COVID-19 era could influence resistance transmission. Importantly, the study provides a contemporary regional snapshot rather than a formal before-and-after analysis of the pandemic.

Key Innovation from the Reference Study

The main innovation is the study’s layered transmission framework. Instead of treating carbapenem resistance as a single phenotype, the investigators combined five complementary perspectives: gene detection, chromosome-versus-plasmid localization, antimicrobial susceptibility, experimental conjugation, and strain-level fingerprinting. This design distinguishes several biologically different routes to dissemination.

Plasmid localization and conjugation address horizontal dissemination, in which resistance determinants move between bacterial cells. ERIC-PCR clustering addresses a different question: whether closely related bacterial lineages are circulating across wards or hospitals, representing a form of vertical dissemination. Adding mobile genetic element analysis provides another layer by identifying sequence environments that may facilitate gene movement. This integrated approach is more informative than reporting carbapenem resistance rates alone and is particularly relevant to antimicrobial resistance research conducted in hospital networks.

The study is also useful because it examines E. cloacae, a clinically important but less frequently characterized CRE species than Klebsiella pneumoniae or Escherichia coli. Its findings help place carbapenemase transmission within the ecology of Enterobacterales rather than focusing exclusively on the most commonly reported species.

Methods and Experimental Design Insights

The investigators analyzed 54 CREC isolates obtained from eight teaching hospitals in Guangdong between December 2022 and June 2024. The workflow was designed to connect molecular results with phenotypic and epidemiological observations. It was a clinical-isolate surveillance study, not a controlled bacterial infection model, so its strength is ecological relevance rather than experimental manipulation of infection conditions.

Protocol Parameters

The following parameters describe the reference study’s design. They should be interpreted as literature-backed features of this investigation, not as universal requirements for every laboratory workflow.

• Isolate collection: 54 carbapenem-resistant E. cloacae isolates from eight teaching hospitals, collected from December 2022 through June 2024; this design supports multicenter comparison but remains geographically restricted.
• CEG detection and localization: variable-temperature sodium dodecyl sulfate plasmid elimination was combined with PCR to assess whether detected genes were associated with plasmid or chromosomal DNA.
• Susceptibility testing: broth microdilution was used to compare antimicrobial resistance patterns between CEG-positive and CEG-negative groups, including imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin.
• Transfer assessment: plasmid conjugation experiments followed by PCR were used to test whether CEGs could be transferred into a recipient background. Reporting transfer rates by gene type was important because different carbapenemase genes behaved differently.
• Genetic relatedness: ERIC-PCR and NTSYS software were used to classify the 54 isolates into fingerprinting genotypes, providing a practical estimate of clonal relatedness across hospitals and departments.
• Mobile-element profiling: six mobile genetic element types were evaluated, allowing the investigators to examine the genetic context surrounding resistance beyond the CEG itself.

For a follow-up study, this design could be strengthened by adding whole-genome sequencing, complete plasmid assembly, and longitudinal sampling. Those additions would be workflow extensions rather than findings reported by Chen et al. They would help resolve whether isolates with similar ERIC-PCR profiles share the same plasmid backbone or merely have related chromosomal fingerprints.

Core Findings and Why They Matter

CEGs were detected in 46 of the 54 isolates, corresponding to 85.19% of the cohort, according to the reference study. The distribution strongly favored bla_NDM−1. Eighteen isolates carried bla_NDM−1 on both chromosome and plasmid, while 25 carried it exclusively on plasmids. Two isolates carried only plasmid-borne bla_IMP, and one carried both plasmid-borne bla_NDM−1 and bla_KPC−2. This pattern emphasizes that plasmids were a major reservoir for carbapenemase genes in the sampled CREC population.

The plasmid finding has direct epidemiological significance. A chromosomal resistance determinant may disseminate primarily with the bacterial lineage, whereas a plasmid-associated determinant can potentially move across strains or species. The coexistence of chromosomal and plasmid locations in some bla_NDM−1-positive isolates also suggests that resistance maintenance may involve more than one genetic compartment. However, localization by plasmid elimination and PCR should be considered supportive rather than equivalent to complete genome-resolved mapping.

CEG-positive isolates showed significantly higher resistance rates than CEG-negative isolates to imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin, with P<0.05 for the reported comparisons, as described in the published results. The ciprofloxacin and levofloxacin findings are important for assay interpretation: they indicate broader multidrug-resistance phenotypes in the CEG-positive group, but they do not demonstrate that carbapenemase genes directly cause fluoroquinolone resistance. Fluoroquinolone resistance can involve target alterations, efflux, permeability changes, and acquired resistance determinants, and these mechanisms were not fully resolved in this study.

Conjugation experiments provided particularly strong evidence for transfer potential. CEG transfer was successful for 44 of 46 CEG-positive isolates, or 95.65%. The reported gene-specific success rates were 42 of 44 for bla_NDM−1, 2 of 2 for bla_IMP, and 0 of 1 for bla_KPC−2. The contrast between highly transferable bla_NDM−1 and the non-transferred bla_KPC−2 isolate illustrates why gene-level analysis is more informative than assuming that all CEGs have equivalent mobility.

Mobile genetic element results reinforced this interpretation. ISEcp1 was the most prevalent element, detected in 47 of 54 isolates, or 87.04%. The most common pattern involved four mobile genetic element types occurring together in 22 isolates, or 40.74%, according to the study report. These observations are consistent with a highly mobile resistance environment, although the presence of an insertion sequence alone does not prove that it mediated a particular transfer event.

ERIC-PCR divided the isolates into 17 genotypes. Types E and G were each observed in 11 of 54 isolates, or 20.37%, and occurred in different departments across five hospitals. Two type E strains shared a Dice coefficient of 100%. Together, the results support both horizontal and vertical dissemination: conjugation supports plasmid transfer, while repeated genotypes across clinical locations suggest circulation of related bacterial lineages. The epidemiological distribution was highest among male patients, older individuals, respiratory medicine patients, and sputum specimens, but these categories describe detection patterns rather than independent risk factors.

Comparison with Existing Internal Articles

The internal article Ciprofloxacin in Resistance Gene Transmission: Unveiling Laboratory Insights focuses on how a fluoroquinolone antibiotic can be incorporated into laboratory studies of resistance and gene dissemination. Its conceptual emphasis complements the present paper’s observation that CEG-positive CREC also had higher ciprofloxacin resistance. The two topics should not be treated as interchangeable: Chen et al. measured ciprofloxacin susceptibility as part of a clinical isolate panel, whereas the internal article is oriented toward experimental workflow design.

Similarly, Ciprofloxacin for Precision Antibacterial Assays: Mechanism and Model Design discusses assay interpretation through the fluoroquinolone mechanism of action, including bacterial DNA replication inhibition. That framework is useful when designing follow-up susceptibility or selection experiments, but the Guangdong study did not directly measure DNA gyrase inhibition, topoisomerase IV inhibition, or ciprofloxacin target mutations. The appropriate connection is therefore methodological: ciprofloxacin phenotypes can be used to motivate additional mechanistic testing, not to infer a mechanism absent from the reference data.

Limitations and Transferability

Several limitations affect how broadly the findings should be applied. First, the sample included 54 isolates from eight teaching hospitals in one Chinese province. The high CEG detection rate is therefore a cohort result, not a population prevalence estimate for all hospitals, regions, or Enterobacter species.

Second, the study period does not include a clearly defined pre-pandemic comparator. The background appropriately identifies antibiotic use and healthcare disruption as possible influences, but the data cannot establish that the COVID-19 pandemic changed CEG frequency or transmission dynamics. A longitudinal design with standardized sampling before, during, and after the pandemic would be needed for that inference.

Third, variable-temperature SDS plasmid elimination and PCR can support localization, but they do not provide the complete sequence, copy number, plasmid backbone, or genomic neighborhood of each resistance gene. Conjugation demonstrates transfer under laboratory conditions; it does not measure transfer frequency in patients or prove that a specific clinical transmission event occurred. Likewise, ERIC-PCR is useful for screening relatedness but generally offers less resolution than whole-genome sequencing. A shared fingerprint can indicate related isolates without proving direct patient-to-patient transmission.

Finally, the association between CEG status and ciprofloxacin resistance should be interpreted cautiously. The study did not identify the molecular basis of fluoroquinolone resistance, quantify prior antibiotic exposure, or establish whether isolates represented infection, colonization, or repeated sampling from the same patient. These gaps limit causal interpretation but do not diminish the paper’s central contribution: combining mobility and clonality measurements provides a stronger basis for infection-control research than resistance phenotyping alone.

Research Support Resources

For laboratories extending this work into comparative susceptibility testing, selection experiments, or resistance surveillance, researchers can use Ciprofloxacin (SKU A8399), a fluoroquinolone antibiotic that targets bacterial DNA gyrase and topoisomerase IV. The product information reports high purity and recommends attention to solvent compatibility, storage at −20°C, and prompt use of prepared solutions. These practical considerations should be matched to the laboratory’s validated assay conditions and biosafety procedures.