Gene Editing of Staphylococcus aureus Phage (S. aureus Phage)
1.ResearchBackground
Staphylococcus aureus is a key pathogen causing severe clinicalinfections. Its drug resistance, represented by MRSA, has posed a hugechallenge to public health. As a natural “nanoweapon” that precisely targetspathogenic bacteria, phage therapy shows great potential in the treatment ofdrug-resistant bacterial infections. Precise and efficient gene editingtechnology is a critical tool for improving phage lysis efficiency, broadeninghost ranges, reducing immunogenicity, and developing novel phage-derived drugs.
Against this background, Shutong Biotechnology provides customizedengineering services for Staphylococcus aureus phages. Using theCRISPR/Cas9 system as a robust reverse selection tool combined with homologousrecombination, we can achieve precise targeted gene knockout, site-directedmutagenesis, and functional fragment integration (such as overexpression ofdepolymerases) in phage genomes. We are committed to providing professional andreliable gene editing solutions for Staphylococcus aureus phages for globalcustomers in scientific research and clinical translation.
2. Host Characteristics and Biological Background
(1) Host cell wall barrier:
Staphylococcus aureus is a Gram‑positive bacterium with a thickpeptidoglycan cell wall of 20–80 nm. This structure acts not only as a barrierto phage infection, but also as the major physical obstacle for gene-editingplasmids to enter the cell.
(2) Clinical relevance:
Engineering phages targeting highly virulent lineages such as MRSAand USA300 represents a key challenge in addressing clinical drug-resistantinfections.
(3) Environmental adaptability:
Staphylococcus aureus exhibits strong biofilm formation capacity.Editing phages to express biofilm-degrading enzymes has become a major focus ofcurrent research.
3. Reported Editing Strategies
Given the difficulties in genetic manipulation of Staphylococcusaureus and its phages, the mainstream gene editing strategies currentlyused include:
3.1 CRISPR/Cas9 Selection System (Mainstream Strategy)
(1) Principle: The Cas9 protein, guided by sgRNA, performssite-specific cleavage of the wild-type phage genome.
(2) Advantages: Since wild-type phages are cleaved by Cas9 and losereplication ability, phages with homologous recombination-mediated mutationscan be efficiently enriched and screened.
3.2 Homologous Recombination
Used with shuttle plasmids, precise base substitution or sequenceinsertion is achieved via upstream and downstream homologous arms.
3.3 Optimization of Transformation and Infection Efficiency
For clinical isolates and their corresponding phages,electroporation conditions are optimized, or restriction-modification-deficientrecipient strains are used to overcome transformation barriers.
4. Core Application Areas
(1) Functional Genomics:
Precise deletion or modification of phage early or late genes toinvestigate their effects on the lytic cycle and progeny packaging.
(2) Host Range Engineering:
Site-directed mutagenesis or domain swapping of tail fiber proteinsenables specific recognition of S. aureus strains of differentserotypes.
(3) Synthetic Biology Applications:
Integration of reporter genes (e.g., fluorescent proteins) into thephage genome for real-time monitoring of the infection process.
(4) Engineered Phage Development:
Integration of endolysin or depolymerase genes to enhance thepenetration ability of phages into complex biofilm structures.
5. Project Workflow and Validation
We provide a one-stop service from design to delivery to guaranteethe accuracy of editing results:
(1) Protocol Design and Vector Construction:
Design of donor plasmids containing mutation templates and sgRNAexpression vectors targeting phage loci.
(2) Host Transformation and Infection:
After introducing plasmids into S. aureus recipient strains,wild-type phages are inoculated to conduct homologous recombination andCas9-mediated selection.
(3) Single Plaque Purification and Multiple Validation:
Pure positive mutant phage strains are confirmed by PCRidentification and Sanger sequencing.
6. Introduction to Gene Editing Projects
6.1 Core Services
(1) Gene Knockout / Inactivation
Precise deletion of non-essential genes for functional research orreduction of genome load.
(2) Gene Integration / Overexpression
Insertion of reporter genes or functional enzyme tags at non-codingregions or specific loci.
(3) Point Mutation / Modification
Simulation of natural variations or engineering of proteinfunctional sites to analyze drug resistance and inhibition mechanisms.
(4) Customized Solutions
Design of optimal editing strategies for phages of differentorigins (temperate or virulent).
6.2 Technical Advantages
(1) High Success Rate
The independently developed CRISPR/Cas9 negative selection platformensures efficient identification of mutant strains.
(2) Full‑Process Validation
Complete validation reports ranging from single plaque screening towhole‑genome sequencing are provided.
(3) Marker‑Free Editing
No unnecessary resistance markers are introduced, fully complyingwith subsequent biosafety evaluation.
7. Case Introduction
We have successfully provided services for many top universities,research institutes and biotechnology companies at home and abroad. Selectedexamples are as follows:
Case: CRISPR‑Cas9 Mediated Efficient Genome Engineering of StrictlyLytic Staphylococcus aureus Phage K
Project Content:
A phage engineering platform based on CRISPR‑Cas9‑assistedhomologous recombination was developed. The strictly lytic staphylococcal phageK with broad host range was successfully engineered, and a reporter phage forrapid detection of Staphylococcus aureus was constructed.
(1) Research Background
Staphylococcus aureus is an important opportunistic pathogen, andits drug resistance (e.g., MRSA and VRSA) has become increasingly severe. As apromising alternative strategy, phage therapy still faces challenges in theengineering of large‑genome phages.
Phages of the subfamily Twortvirinae (such as phage K) areideal candidates due to their strict lytic phenotype and broad host range.However, their large genome (~148 kb) makes them difficult to engineer usingtraditional synthetic biology methods.
This study aimed to develop a high‑efficiency engineering platformto break through this technical bottleneck and provide novel tools for preciseantibacterial therapy and diagnosis.
(2) Protocol Design
The research team established a two‑step engineering platform(homologous recombination + CRISPR‑Cas9 counter‑selection). The core workflowis as follows:
Engineering Strategy:
Using phage K as the backbone, the nanoluciferase gene (nluc)was inserted into the high‑expression region of the major capsid protein gene (cps)to construct the reporter phage K::nluc.
The homologous recombination plasmid pEDITnluc was used toprovide homologous arms and silent PAM mutations to avoid cleavage by CRISPR‑Cas9.
CRISPR‑Cas9 Counter‑Selection System:
The plasmid pSELECTcps (expressing Cas9 and sgRNA targetingthe wild‑type phage) was introduced into the host strain RN4220 to specificallyeliminate non‑recombinant phages and enrich recombinants (escape frequency ≈10⁻⁴).
The correct genotype of the recombinant phage was verified by PCRand sequencing.
Performance Validation System:
Host range was evaluated by efficiency of plating (EOP) assays;sensitivity was detected by bioluminescence kinetics assays; real‑worldapplication scenarios were simulated in complex matrices (whole blood, rawmilk).
(3) Experimental Conclusions
Highly Efficient Detection by Phage Display:
K::nluc generated bioluminescent signals against all 71 clinicalisolates, including VSSA, VISA, and VRSA. It successfully detected 20 strainsthat produced no plaques, with a sensitivity of 10²–10³ CFU/mL. The luminescentsignal peaked within 3 hours (approximately 10⁶-fold increase in RLU) andshowed consistent performance across strains with different drug-resistantphenotypes.
Retention of Activity in Complex Matrices:
The limit of detection (LOD) in whole blood was 136–2,151 CFU/mL(citrate anticoagulant performed better than heparin); in raw milk, the LOD was55–514 CFU/mL, demonstrating strong resistance to matrix interference.
Controllable Impact of Phage Engineering:
The plaque area of K::nluc was slightly smaller than that of thewild-type phage (reduced by 0.07 mm²), but this did not compromise itspractical performance.
(4) Application Significance
Diagnostic Potential:
K::nluc enables rapid detection (within 3 hours) of viablebacteria, outperforming traditional culture methods, and is suitable for earlydiagnosis of bacteremia and bovine mastitis. It can generate signals evenduring "ineffective infection" of some drug-resistant strains,expanding the scope of detection.
Value as a Therapeutic Development Platform:
This platform provides a universal strategy for engineering Twortvirinaephages. In future applications, it can be loaded with antibacterial effectorgenes (e.g., lysozyme genes) for the treatment of chronic infections. It offerstechnical support for precision therapies against drug-resistant bacteria,especially in critical scenarios where antibiotics are ineffective.
Limitations and Prospects:
The current system relies on the RN4220 host strain and needs to beextended to more clinical strains. Future work will explore its detectioncapability for dormant bacteria and combination with other detectiontechnologies.
Cooperate With Us
By choosing us, you will gain a highly experienced and technicallycompetent partner in gene editing. We are committed to advancing your researchor projects efficiently through professional expertise, rigorous procedures,and effective communication.
Consult now to get your customized gene editing solution and quote!
