AbstractStaphylococcus aureus can cause a variety of infections, many of which involve biofilm infections. Inside biofilms, growing and non-growing bacteria such as persisters co-exist, making it challenging to completely eradicate a persistent and recurrent infection with current treatments. Despite the clinical relevance, most of the current antibiotic treatments mainly kill the growing bacteria and have poor activity against non-growing persister bacteria and thus have limited effect on treating persistent infections including biofilm infections. We previously proposed a Yin-Yang model using a drug combination approach targeting both growing bacteria and persister bacteria for more effective clearance of persistent infections. Here, as a proof of principle, we showed that combining drugs that have high activity against growing forms, such as vancomycin or meropenem, with drugs that have robust anti-persister activity, such as clinafloxacin and oritavancin, could completely eradicate S. aureus biofilm bacteria in vitro. In contrast, single or two drugs including the current treatment for persistent S. aureus infection doxycycline plus rifampin failed to kill all biofilm bacteria in vitro. We then developed a chronic persistent skin infection mouse model with biofilm-seeded bacterial inocula demonstrating that biofilm bacteria caused more severe and persistent skin lesions than log phase S. aureus bacteria. More importantly, we found that the drug combination which eradicated biofilm bacteria in vitro is more efficacious than current treatments and completely eradicated S. aureus biofilm infection in mice. The complete eradication of biofilm bacteria is attributed to the unique high anti-persister activity of clinafloxacin, which could not be replaced by other fluoroquinolones such as moxifloxacin, levofloxacin or ciprofloxacin. Our study is the first to demonstrate that the combination of meropenem, daptomycin, plus clinafloxacin completely cleared the persistent infection, healed the lesions, and had less inflammation, while mice treated with doxycycline plus rifampin, the current clinically recommended treatment for chronic tissue infection, failed to do so. We also compared our persister drug combination with other approaches for treating persistent infections including gentamicin+fructose and ADEP4+rifampin in the S. aureus biofilm infection mouse model. Neither gentamicin+fructose nor ADEP4+rifampin could eradicate or cure the persistent biofilm infection in mice. In contrast, our drug combination regimen with persister drug clinafloxacin plus meropenem and daptomycin completely eradicated and cured the persistent biofilm infection in 7 days. An unexpected observation is that ADEP4 treatment group developed worsened skin lesions and caused more extensive pathology than the untreated control mice. Our study demonstrates an important treatment principle for persistent infections by targeting both growing and non-growing heterogeneous bacterial populations utilizing persister drugs for more effective eradication of persistent and biofilm infections. Our findings may have implications for improved treatment of many other persistent infections in general.
Comparison of in vitro static and dynamic assays to evaluate the efficacy of an antimicrobial drug combination against Staphylococcus aureus