Fibroblast Protection of Borrelia burgdorferi from Doxycycline, Cefuroxime and Daptomycin Combination is Eliminated by Oregano or Carvacrol Essential Oil

Borrelia burgdorferi could be occasionally recovered from patients after antibiotic treatment, which indicates it may resist eradication by antibiotic and host defense mechanisms. Skin fibroblast cells have previously been shown to protect the killing of B. burgdorferi by ceftriaxone, a powerful antibiotic commonly used to treat Lyme disease. In this study, we evaluated if fibroblast cells could also protect against the doxycycline+ cefuroxime+ daptomycin drug combination which has previously been shown to completely eradicate highly persistent biofilm-like microcolonies of B. burgdorferi. To do so, we utilized a GFP-labeled B. burgdorferi for infection of murine fibroblast cells and assessed the effect of the drug combination on killing the bacteria in the presence or absence of the fibroblast cells. Surprisingly, we found that fibroblasts could protect B. burgdorferi from being completely killed by the drug combination doxycycline, cefuroxime and daptomycin, which eradicated B. burgdorferi completely in the absence of fibroblast cells. Interestingly, addition of essential oil carvacrol or oregano at 0.1% could enhance the activity of the doxycycline+ cefuroxime+ daptomycin drug combination and led to complete eradication of B. burgdorferi even in the presence of fibroblast cells. Further studies are needed to determine if the essential oil drug combinations could eradicate persistent B. burgdorferi infection in vivo in animal models. Our study provides a useful and convenient ex vivo model for evaluating different drug regimens needed for developing more effective treatment of persistent Lyme disease in the future.