Abstract
Osteomyelitis, or bone infection, is often induced by antibiotic resistant Staphylococcus aureus strains of bacteria. Although debridement and long-term administration of antibiotics are the gold standard for osteomyelitis treatment, the increase in prevalence of antibiotic resistant bacterial strains limits the ability of clinicians to effectively treat infection. Bacteriophages (phages), viruses that in a lytic state can effectively kill bacteria, have gained recent attention for their high specificity, abundance in nature, and minimal risk of host toxicity. Previously, we have shown that CRISPR-Cas9 genomic editing techniques could be utilized to expand temperate bacteriophage host range and enhance bactericidal activity through modification of the tail fiber protein. In a dermal infection study, these CRISPR-Cas9 phages reduced bacterial load relative to unmodified phage. Thus we hypothesized this temperate bacteriophage, equipped with the CRISPR-Cas9 bactericidal machinery, would be effective at mitigating infection from a biofilm forming S. aureus strain in vitro and in vivo. In vitro, qualitative fluorescent imaging demonstrated superiority of phage to conventional vancomycin and fosfomycin antibiotics against S. aureus biofilm. Quantitative antibiofilm effects increased over time, at least partially, for all fosfomycin, phage, and fosfomycin-phage (dual) therapeutics delivered via alginate hydrogel. We developed an in vivo rat model of osteomyelitis and soft tissue infection that was reproducible and challenging and enabled longitudinal monitoring of infection progression. Using this model, phage (with and without fosfomycin) delivered via alginate hydrogel were successful in reducing soft tissue infection but not bone infection, based on bacteriological, histological, and scanning electron microscopy analyses. Notably, the efficacy of phage at mitigating soft tissue infection was equal to that of high dose fosfomycin. Future research may utilize this model as a platform for evaluation of therapeutic type and dose, and alternate delivery vehicles for osteomyelitis mitigation.
Highlights
For nearly a century, antibiotics have been a vital resource utilized by clinicians to eliminate infection, with nearly 270 million prescriptions dispensed in 2015 alone.[1]
These results demonstrated that S. aureus ATCC 6538 chromosomally integrated with green fluorescent protein (GFP) can be used for real-time monitoring of bacterial proliferation in vitro and in vivo
A previously developed CRISPR-Cas9 modified bacteriophage therapeutic, which was successful in treating external dermal infection[21], was evaluated as a therapeutic for internal osteomyelitis and contiguous soft tissue infection in a rat model using a biofilm forming strain of S. aureus
Summary
Antibiotics have been a vital resource utilized by clinicians to eliminate infection, with nearly 270 million prescriptions dispensed in 2015 alone.[1] Antibiotics are utilized for a variety of infections, from common otitis externa (“swimmers ear”) to severe endocarditis, pneumonia, meningitis or osteomyelitis. Antibiotics are typically able to clear infection, antibiotic resistant strains of bacteria continue to emerge. It is not as lucrative, nor as feasible, for pharmaceutical companies to develop novel antibiotics at the rates that these multi-drug resistant (MDR) bacterial strains are isolated. Approximately $2.2 billion is spent annually to treat MDR bacterial infections.[2] By 2050, it is estimated that nearly 10 million people could die each year due to resistant strains of bacteria.[3]
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