Staphylococcus aureus Phage Genome Editing Service

Staphylococcus aureus Phage Genome Editing Service

1. Research Background

Staphylococcus aureus is a core pathogen responsible for clinical severe infections, and its drug resistance (e.g., MRSA) poses enormous challenges to public health. As a natural "nanoweapon" for the precise targeting of pathogenic bacteria, phage therapy has shown great potential in the treatment of drug-resistant bacterial infections. Precise and efficient genome editing technologies are key tools for enhancing phage lytic efficiency, broadening host range, reducing immunogenicity, and developing novel phage-derived drugs.

Against this backdrop, GeneRulor launches customized modification services for S. aureus phages. By utilizing the CRISPR/Cas9 system as a powerful negative selection tool combined with homologous recombination technology, we can achieve precise target gene knockout, site-directed mutagenesis, and functional fragment integration (e.g., depolymerase overexpression) in the phage genome. We are committed to providing professional and reliable S. aureus phage genome editing solutions for scientific research and clinical translation clients worldwide.

2. Host Characteristics and Biological Background

（1）Host Cell Wall Barrier: S. aureus is a Gram-positive bacterium with a peptidoglycan cell wall 20–80 nm thick. This structure acts not only as a barrier to phage infection but also as the main physical obstacle for gene-editing plasmids to enter cells.

（2） Clinical Relevance: The modification of phages targeting highly virulent lineages such as MRSA and USA300 is a core challenge in addressing clinical drug-resistant infections.

（3）Environmental Adaptability: S. aureus has a strong ability to form biofilms, and engineering phages to express biofilm-degrading enzymes is a current research hotspot.

Figure 1 Plaques formed by S. aureus phages infecting host bacteria

3. Reported Editing Strategies

In view of the difficulties in genetic manipulation of S. aureus and its phages, the currently mainstream editing strategies include:

3.1 CRISPR/Cas9 selection pressure system (primary protocol):

（1）Principle: The Cas9 protein, guided by sgRNA, mediates site-specific cleavage of the wild-type phage genome.

（2）Advantages: Cleaved wild-type phages lose the ability to replicate, allowing phages with homology-directed repair mutations to be selectively enriched, thus achieving highly efficient screening.

3.2 Homologous Recombination:

Used in conjunction with shuttle plasmids to achieve precise base substitution or sequence insertion via upstream and downstream homologous arms.

3.3 Optimization of Transformation and Infection Efficiency:

For clinically isolated strains and their corresponding phages, optimize electroporation conditions or use recipient bacteria deficient in restriction-modification systems to overcome transformation barriers.

4. Core Application Fields

（1）Functional Genomics: Precisely delete or modify early or late phage genes to investigate their effects on the lytic cycle and progeny packaging.

（2）Host Range Modification: Achieve precise recognition of different S. aureus serotypes through site-directed mutagenesis or domain swapping of tail fiber proteins.

（3）Synthetic Biology Applications: Integrate reporter genes (e.g., fluorescent proteins) into the phage genome to enable real-time monitoring of the infection process.

（4）Engineered Phage Development: Integrate endolysin or depolymerase genes to enhance the phage's ability to penetrate complex biofilm structures.

5. Project Process and Validation

We offer one-stop services from design to delivery to ensure the accuracy of editing results:

（1）Protocol Design and Vector Construction: Design donor plasmids containing mutation templates and sgRNA expression vectors targeting phage loci.

（2）Host Bacterium Transformation and Phage Infection: After introducing plasmids into S. aureus recipient strains, inoculate wild-type phages for homologous recombination and Cas9 pressure screening.

（3）Single Plaque Purification and Multiplex Validation: Obtain pure positive mutant phage strains verified by PCR and Sanger sequencing.

Figure 2 Schematic of the Project Process

6. Introduction to Genome Editing Projects

6.1 Our core services include:

（1）Gene Knockout/Inactivation: Precisely delete non-essential genes to study their functions or reduce genomic load.

（2）Gene Integration/Overexpression: Insert reporter genes or functional enzyme tags into non-coding regions or specific loci.

（3）Site-Directed Mutagenesis/Modification: Mimic natural variations or modify protein functional sites to elucidate the mechanisms of drug resistance inhibition.

（4）Customized Protocols: Design optimal editing strategies for phages of different origins (temperate or lytic).

6.2 Technical Advantages

（1）High Success Rate: Our independently developed CRISPR/Cas9 negative selection platform ensures the efficient detection of mutant strains.

（2）Full-Process Validation: Provide a complete validation report ranging from single plaque screening to whole-genome sequencing.

（3）Scarless Editing: No unnecessary resistance markers are introduced, fully complying with subsequent biosafety evaluations.

7. Case Introduction

We have successfully provided services for numerous top universities, research institutions, and biotech companies at home and abroad. A representative case is presented below:

Case: CRISPR-Cas9-Mediated Efficient Genome Engineering of the Strictly Lytic Staphylococcus aureus Phage K

Project Content: Developed a phage engineering platform based on CRISPR-Cas9-assisted homologous recombination, successfully modified the strictly lytic staphylococcal phage K with a broad host range, and constructed a reporter phage for the rapid detection of S. aureus.

（1）Research Background

Staphylococcus aureus is an important opportunistic pathogen with an increasingly severe drug resistance problem (e.g., MRSA and VRSA). Phage therapy has potential as an alternative strategy, but the engineering of large-genome phages still faces challenges. Phages of the Twortvirinae subfamily (e.g., phage K) are ideal candidates due to their strict lytic property and broad host range, yet their large genome (approximately 148 kb) is difficult to modify via traditional synthetic biology methods. This study aimed to develop a highly efficient engineering platform to break through this technical bottleneck and provide new tools for precise antibacterial therapy and diagnosis.

（2）Protocol Design

The research team established a two-step engineering platform (homologous recombination + CRISPR-Cas9 counterselection), with the core process as follows:

Engineering Strategy: Using phage K as the backbone, insert the nano-luciferase gene (nluc) into the high-expression region of its major capsid protein gene (cps) to construct the reporter phage K::nluc. The homologous recombination plasmid pEDITnluc was used to provide homologous arms and silent PAM mutations to avoid CRISPR-Cas9 cleavage.

CRISPR-Cas9 Counterselection System: Introduce the pSELECTcPS plasmid (expressing Cas9 and sgRNA targeting wild-type phages) into the host strain RN4220 to specifically eliminate non-recombinant phages and enrich recombinants (escape frequency of approximately 10⁻⁴). The correct genotype of recombinant phages was verified by PCR and sequencing.

Performance Validation System: Evaluate host range via the efficiency of plating (EOP) assay; detect sensitivity via bioluminescence kinetic experiments; and simulate practical application scenarios in complex matrices (whole blood, raw cow's milk).

（3）Experimental Conclusions

Reporter Phage Exhibits High-Efficiency Detection Capability:

K::nluc produced bioluminescent signals for all 71 clinically isolated strains (including VSSA, VISA, and VRSA), and even 20 strains without plaque formation could be detected (sensitivity up to 10²–10³ CFU/mL). The luminescent signal reached a peak within 3 hours (an approximate 10⁶-fold increase in RLU) and was consistent across strains with different drug resistance phenotypes.

Maintains Activity in Complex Matrices:

The limit of detection (LOD) in whole blood was 136–2,151 CFU/mL (citrate as an anticoagulant was superior to heparin); the LOD in raw cow's milk was 55–514 CFU/mL, demonstrating strong resistance to matrix interference.

Controllable Impact of Engineering on Phage Properties:

The plaque area of K::nluc was slightly smaller than that of the wild type (a reduction of 0.07 mm²), but this did not affect practical application effects.

（4）Application Significance

Diagnostic Potential: K::nluc enables rapid detection (within 3 hours) of viable bacteria, outperforming traditional culture methods, and is suitable for the early diagnosis of bacteremia and bovine mastitis. "Non-productive infection" of some drug-resistant bacteria still generates signals, expanding the detection range.

Value as a Therapeutic Development Platform: This platform provides a universal strategy for the engineering of Twortvirinae phages. In the future, it can be loaded with antibacterial effector genes (e.g., lysozyme) for the treatment of chronic infections, and provides technical support for precise therapy against drug-resistant bacteria, especially for critical scenarios where antibiotics fail.

Limitations and Prospects: The current system relies on the RN4220 host and needs to be extended to more clinical strains; future research can explore the ability to detect dormant bacteria and combination with other detection technologies.

8. References

[1] Tong, S. Y., et al. (2015). Staphylococcus aureus infections: Epidemiology, pathophysiology, clinical manifestations, and management. Clinical Microbiology Reviews.

[2] Bruckner, R. (1997). Gene replacement in Staphylococcus aureus via homologous recombination. Methods in Molecular Biology.

[3] Jiang, W., et al. (2013). RNA-guided editing of bacterial genomes using CRISPR-Cas systems. Nature Biotechnology.

[4] Luo, M. L., et al. (2016). The CRISPR-Cas9 system as a tool for editing the genomes of Staphylococcus aureus. Applied and Environmental Microbiology.

[5] J. Fernbach et al., (2025). CRISPR-Cas9 enables efficient genome engineering of the strictly lytic, broad-host-range staphylococcal bacteriophage K. Appl. Environ. Microbiol.

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