In-Vitro Susceptibility of Different Morphological Forms of Borrelia Burgdorferi to Common Lyme Antibiotics in Combination with Antimicrobial Peptides

Antimicrobial susceptibility testing was conducted with three antibiotics commonly used to treat Lyme disease (doxycycline, erythromycin, and tinidazole) and three AMPs (cecropin P1, magainin 1, and LL-37) against one strain of Borrelia burgdorferi. The susceptibility of spirochete and spheroplast (cyst) forms was determined by direct cell counting using dark field microscopy. Significant synergy was seen when erythromycin was combined with cecropin P1. Spirochete growth decreased (P=0.0015) and spheroplast (cyst) growth decreased (P=0.001) when compared to the growth control. Synergy was also seen when tinidazole was combined with LL-37. Spheroplast growth decreased (P=0.015). Combining antimicrobial peptides with commonly prescribed antibiotics to treat Lyme disease may provide a new approach to the treatment of chronic infections due to the significant synergistic effect of a combination therapy.