Enterococcus faecalis

Genome Editing Service for Enterococcus faecalis

1. Research Background

Enterococcus faecalis is a significant human commensal and opportunistic pathogen. The nosocomial infections it causes (particularly those by vancomycin-resistant enterococci, VRE) and biofilm-associated infections pose serious challenges in clinical microbiology and public health. Precise and efficient gene-editing technology provides a crucial tool for in-depth analysis of its drug resistance mechanisms, virulence factor regulation, and host adaptation. In this context, we offer microbial genome modification services based on CRISPR/Cas9 and Homologous Recombination, enabling customized gene knockout, site-directed mutagenesis, gene knock-in, and exogenous gene integration in E. faecalis, with delivery of positive mutant strains. We are committed to providing professional and reliable Enterococcus faecalis genome editing solutions for global research and industrial clients.

2. Strain Characteristics and Biological Background

(1) Gram-staining property: Enterococcus faecalis is a Gram-positive bacterium. Its physical characteristics include a thick peptidoglycan cell wall and typical arrangement in pairs or short chains (distinct from the grape-like clusters of staphylococci).

(2) Clinical significance: It is a core member of the human gut microbiota but acts as an opportunistic pathogen, causing urinary tract infections, endocarditis, bacteremia, and wound infections. The widespread dissemination of vancomycin-resistant enterococci (VRE), in particular, has classified it as one of the "ESKAPE" pathogens, rendering it a high-priority research subject.

(3) Metabolism and applications: It exhibits remarkable environmental resilience (tolerant to high salt, bile salts, and extreme pH), making it an ideal model for studying bacterial survival mechanisms under harsh conditions, biofilm formation, and horizontal gene transfer (plasmid conjugation).

Figure 1. Schematic Design of SpCas9-Mediated Gene Editing in Enterococcus faecalis. DOI:10.1093/femsle/fnz256

3. Gene-Editing Strategies Reported in the Literature

To address the transformation and editing efficiency challenges posed by the thick cell wall of E. faecalis, the mainstream optimization strategies in current literature and our adopted methods include:

3.1 CRISPR/Cas9 System (High-Efficiency Solution):

(1) Principle: Utilizes Cas9 proteins or Cas9 variants optimized for Gram-positive bacteria to perform specific cleavage of target genomic DNA under sgRNA guidance.

(2) Advantage: Compared to traditional methods, CRISPR technology significantly shortens construction timelines. It enriches for edited cells by applying lethal selective pressure on unedited cells, thereby greatly improving positive rates. It is suitable for seamless knockout and in-situ genomic modifications.

3.2 Homologous Recombination:

Utilizes thermosensitive suicide plasmids (e.g., derivatives of the pG+host series) to achieve precise allele replacement via double-crossover events mediated by upstream and downstream homologous arms.

3.3 RecT/RecE Recombineering System:

Introduces phage-derived recombinase systems to promote recombination using short homologous arms at specific sites, applicable for high-throughput genome engineering.

3.4 Transformation Efficiency Optimization:

For clinical isolates and multidrug-resistant strains, we have optimized pretreatment steps (e.g., with glycine/lysozyme) and electroporation parameters to effectively overcome the cell wall barrier.

4. Core Application Areas

(1) Drug Resistance Mechanism Analysis: Precise knockout or mutation of cell wall synthesis-related genes (e.g., van gene clusters) to elucidate the resistance mechanisms to vancomycin and novel antibiotics.

(2) Virulence Factor Research: Studying the functions of biofilm formation-related genes (e.g., esp, fsr, gelE) in bacterial colonization and pathogenesis.

(3) Host-Pathogen Interaction: Constructing tracer strains with fluorescent markers (GFP/RFP) for real-time monitoring of bacterial infection dynamics in cell or animal models.

(4) Probiotic Engineering: For non-pathogenic Enterococcus strains, metabolic engineering for synthetic biology product expression or the development of intestinal delivery vectors.

5. Project Workflow and Validation

We provide a one-stop service from design to delivery, ensuring the accuracy of editing outcomes:

(1) Design and Vector Construction: Designing specific sgRNAs and homologous repair templates for target sites, and constructing the editing plasmids.

(2) Bacterial Transformation and Screening: Introducing the constructs into E. faecalis using optimized electroporation protocols, followed by selection of transformants via antibiotics and phenotype screening.

(3) Multi-level Validation: Primary screening via colony PCR, with final confirmation of the edited region's sequence accuracy through Sanger sequencing or whole-genome sequencing.

Figure 2. Schematic Diagram of Project Workflow

6. Genome Editing Project Introduction

6.1 Core services include:

(1) Gene Knockout/Inactivation: Precise deletion of target genes (e.g., the gelEgelatinase gene) to construct loss-of-function mutant strains.

(2) Gene Knock-in/Overexpression: Insertion of exogenous genes or strong promoters at specific genomic loci (e.g., intergenic regions of rRNA operons or neutral sites).

(3) Point Mutation/In-situ Modification: Introduction of specific single-base mutations to mimic drug resistance sites or study the function of key protein domains.

(4) Multi-gene Editing: Achieving sequential editing at multiple loci to construct multi-deletion or multi-functional engineered strains.

6.2 Technical Advantages:

(1) High Success Rate: Possession of established protocols for E. faecalis standard strains (OG1RF, JH2-2) and clinical resistant strains (V583).

(2) Marker-free Editing: Final delivered strains can be cured of antibiotic resistance markers and plasmid backbones, eliminating interference in subsequent experiments.

(3) End-to-End Validation: Data is authentic and reliable, with complete reports including electrophoretograms and sequencing chromatograms provided.

7. Case Studies

We have successfully provided services for numerous top universities, research institutes, and biotech companies both domestically and internationally. Below is an example:

Case Study: The R&D team at Zhuhai ShuTong Medical has developed a SpCas9 editing system specifically for Enterococcus faecalis. We successfully achieved the insertion of large exogenous DNA fragments (1,500-3,000 bp) into the E. faecalis genome with an editing efficiency of 50%. This large fragment included an mCherry sequence, enabling the edited strains to exhibit red fluorescence. Additionally, we have achieved large-fragment deletion in E. faecalis with an efficiency of 80%.

Figure 3. Monoclonal Identification of Target Gene Knock-in and Fluorescence Expression

Figure 4. PCR Identification Confirming Successful Target Gene Knockout

8. References

[1] Hullahalli, K., et al. (2015). A CRISPR-Cas9 Toolkit for Genome Editing in Enterococcus faecalis. mBio.

[2] Bae, T., et al. (2002). Improvements to the Suicide Vector-Based Genome Modification System in Enterococcus faecalis. Plasmid.

[3] Thurlow, L. R., et al. (2009). GelE function in a clinical isolate of Enterococcus faecalis. Infection and Immunity.

[4] Kristich, C. J., et al. (2007). Development of a Broad-Host-Range Markerless Gene Deletion System for Enterococcus faecalis and Its Use To Inactivate the epb Locus. Applied and Environmental Microbiology.

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