Carbapenemase Gene Spread in CREC, Guangdong

Carbapenem-resistant Enterobacter cloacae complex is an important component of the broader carbapenem-resistant Enterobacteriaceae problem. The reference study, published in BMC Microbiology in 2025, examines how carbapenemase-encoding genes are distributed and transmitted among clinical isolates collected from eight teaching hospitals in Guangdong Province, China. Rather than treating resistance as a purely phenotypic property, the investigators linked gene location, conjugative transfer, mobile genetic elements, antimicrobial susceptibility, strain relatedness, and patient or specimen characteristics.

Study Background and Research Question

Carbapenem resistance in E. cloacae can arise through several mechanisms, but carbapenemase-encoding genes are particularly consequential because they may hydrolyze carbapenems and travel between bacteria on mobile DNA. The authors frame their work against the intensified antibiotic pressure and disrupted healthcare conditions associated with the COVID-19 era. However, the study was designed primarily as a contemporary molecular epidemiology investigation rather than as a formal pre-pandemic versus post-pandemic comparison.

The research question was therefore twofold: which carbapenemase-encoding genes were present in carbapenem-resistant E. cloacae isolates, and what evidence supported their horizontal and vertical dissemination across hospitals? The dataset included 54 isolates collected between December 2022 and June 2024. The reference study also evaluated whether gene carriage was associated with broader antimicrobial resistance and described the clinical distribution of the isolates.

Key Innovation from the Reference Study

The study’s main innovation is its integrated transmission framework. Many surveillance reports identify resistance genes, while separate investigations assess strain relatedness or plasmid transfer. Here, the authors combined these perspectives in the same CREC collection. Plasmid elimination followed by PCR was used to distinguish chromosomal from plasmid-associated gene carriage; conjugation experiments tested transferability; mobile genetic elements were profiled as possible mobilization contexts; and ERIC-PCR with NTSYS analysis provided a fingerprint-based view of relatedness.

This design allows two dissemination routes to be considered together. Horizontal dissemination is supported when a resistance determinant can move into a recipient strain under laboratory conjugation conditions. Vertical or clonal dissemination is suggested when closely related fingerprint types appear among isolates from different clinical departments or hospitals. Neither line of evidence alone proves a complete transmission chain, but their combination provides a more informative epidemiological model than gene detection alone.

Methods and Experimental Design Insights

Isolate characterization and gene localization

The investigators analyzed CREC isolates using a variable-temperature sodium dodecyl sulfate plasmid elimination method and PCR. This workflow was important because it addressed whether a carbapenemase-encoding gene was retained on a plasmid, detected on the chromosome, or associated with both locations. PCR was also used to identify the principal gene targets reported in the study, including bla_NDM-1, bla_IMP, and bla_KPC-2.

Phenotypic susceptibility testing

Broth microdilution was used to compare antimicrobial resistance between carbapenemase-encoding gene-positive and gene-negative groups. The reported comparisons included imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin. This comparison is useful because it tests whether the molecular category has practical phenotypic meaning beyond carbapenem resistance itself.

Conjugation and strain relatedness

Plasmid conjugation experiments, followed by PCR analysis, assessed whether resistance determinants could be transferred to a recipient background. ERIC-PCR generated genomic fingerprints, and NTSYS software was used to classify the 54 isolates into relatedness groups. These methods are complementary: conjugation addresses mobility of a determinant, whereas ERIC-PCR addresses similarity between bacterial backgrounds.

Protocol Parameters

• Study population: Use the reported collection frame of 54 CREC isolates from eight teaching hospitals, gathered from December 2022 through June 2024, when reproducing the study’s surveillance logic.
• Plasmid localization: Apply variable-temperature SDS plasmid elimination followed by PCR, and interpret altered gene detection cautiously because plasmid curing is an indirect localization method rather than a complete sequence map.
• Susceptibility testing: Use broth microdilution to compare carbapenemase-encoding gene-positive and gene-negative isolates across the reported antimicrobial panel; retain separate molecular and phenotypic records for each isolate.
• Transfer assessment: Pair conjugation experiments with PCR confirmation in recipient colonies. Report transfer by gene type rather than only as an overall percentage, as the reference study showed substantial differences between bla_NDM-1, bla_IMP, and bla_KPC-2.
• Relatedness analysis: Use ERIC-PCR and clustering software as a screening-level approach to identify potentially related isolates, then avoid interpreting a shared fingerprint as proof of directionality or a hospital-to-hospital transmission event.
• Workflow recommendation: For follow-up work, add confirmatory plasmid sequencing or whole-genome approaches where available. This is a methodological extension, not a parameter reported by the reference study.

Core Findings and Why They Matter

High prevalence of carbapenemase-encoding genes

Carbapenemase-encoding genes were detected in 46 of 54 isolates, corresponding to 85.19%, according to the published findings. The distribution was dominated by bla_NDM-1. Eighteen isolates, or 33.33% of the collection, carried bla_NDM-1 on both chromosome and plasmid, while 25 isolates, or 46.30%, carried it exclusively on plasmids. Two isolates contained only plasmid-associated bla_IMP, and one carried plasmid-associated bla_NDM-1 together with bla_KPC-2.

The predominance of plasmid-associated bla_NDM-1 is epidemiologically important. A chromosomal determinant may persist through bacterial replication, but a plasmid-associated determinant can potentially move across strains or species if compatible transfer systems and ecological opportunities are present. The mixed chromosomal and plasmid localization also indicates that a single gene may participate in more than one persistence strategy.

Association with multidrug resistance

The carbapenemase-encoding gene-positive group had significantly higher resistance rates to imipenem, cefepime, gentamicin, ceftazidime/avibactam, ciprofloxacin, and levofloxacin than the gene-negative group, with the study reporting P < 0.05 for these comparisons. This result does not mean that every resistance phenotype was caused by the detected carbapenemase. Instead, it identifies gene-positive CREC as a marker of a broader multidrug-resistant background, potentially reflecting co-carried resistance determinants or shared selective pressures.

Strong laboratory transferability

Conjugation and PCR showed successful carbapenemase-encoding gene transfer for 44 of 46 gene-positive isolates, or 95.65%. Transfer success was 42 of 44 for bla_NDM-1, 2 of 2 for bla_IMP, and 0 of 1 for bla_KPC-2. The small number of bla_IMP and bla_KPC-2 isolates limits comparison, but the overall result supports a high capacity for horizontal dissemination, particularly for the dominant NDM-1 determinant.

Mobile elements and clonal structure

Six mobile genetic element types were identified. ISEcp1 was the most prevalent, occurring in 47 of 54 isolates, or 87.04%. Isolates carrying four mobile-element types simultaneously formed the largest category, comprising 22 of 54 isolates, or 40.74%. These observations support a model in which resistance genes are embedded in complex mobile contexts rather than occurring as isolated genetic events.

ERIC-PCR and NTSYS analysis separated the collection into 17 genotypes. Types E and G were each found in 11 of 54 isolates, or 20.37%, and originated from different departments in five hospitals. Two type E isolates shared a Dice coefficient of 100%. This pattern suggests that both dissemination of related bacterial lineages and movement of mobile resistance elements may contribute to the regional burden. The epidemiological profile was highest among men, older adults, respiratory medicine departments, and sputum specimens: 35 of 54, 39 of 54, 11 of 54, and 18 of 54, respectively, as reported in the reference article.

Comparison with Existing Internal Articles

The internal article Transmission Dynamics of Carbapenemase Genes in CREC in Guangdong provides a broader genomic and epidemiological framing of the same subject area. In comparison, the reference study is especially valuable for its explicit linkage of gene localization, conjugation success, mobile-element profiles, and ERIC-PCR genotypes. The two resources are therefore complementary: one supports high-level interpretation of regional transmission, while the published work supplies the experimental evidence needed to distinguish plasmid mobility from possible clonal spread.

Limitations and Transferability

The findings should be interpreted within the boundaries of the sampling design. The collection was limited to eight teaching hospitals in one Chinese province and included 54 isolates, so prevalence estimates may not represent community settings, non-teaching hospitals, other regions, or other members of the Enterobacteriaceae family. The high conjugation rate demonstrates transfer potential under laboratory conditions, but it does not quantify transmission frequency in patients or hospital environments.

The molecular resolution is also important. Plasmid elimination and PCR can indicate likely localization, but they do not fully resolve plasmid backbone structure, insertion-site architecture, copy number, or the complete set of co-transferred resistance genes. ERIC-PCR is useful for screening relatedness but generally provides less resolution than whole-genome sequencing. Finally, the study’s pandemic rationale does not by itself establish that COVID-19 caused the observed transmission pattern because a matched earlier surveillance period was not presented in the condensed findings. Future studies would benefit from longitudinal sampling, exposure data, and sequence-based reconstruction of plasmid and chromosome relationships.

Why this cross-domain matters, maturity, and limitations

The study provides a strong bridge between molecular epidemiology and laboratory susceptibility workflows. Gene localization and transferability data can guide which isolates deserve deeper phenotypic testing, while susceptibility results can show whether a mobile resistance background coincides with reduced activity across several antibiotic classes. This bridge is mature for surveillance and assay prioritization, but less mature for direct clinical prediction: a transferable gene does not specify treatment outcome, and an in vitro susceptibility result does not capture pharmacokinetics, tissue exposure, or patient-level factors.

Research Support Resources

Researchers extending this framework into standardized susceptibility, mechanism-focused, or antibiotic resistance research workflows can use Ertapenem (sodium salt) (SKU C3451) as a research reagent. It is described as a broad-spectrum antibacterial agent for Gram-positive and Gram-negative bacteria that acts through penicillin-binding protein inhibition. The pharmacokinetics of ertapenem should be considered separately from the gene-transfer evidence in this paper, and the material is intended for scientific research rather than diagnosis or the treatment of bacterial infections.