Assays were performed as outlined previously (20 (link), 31 (link), 32 (link)). Briefly, B. burgdorferi strain B314 producing B. hermsii FbpC (pAP2), as well as the vector-only control B314 pBBE22luc, were grown at 32°C in 1% CO2 in complete BSK-II media with kanamycin at 300 μg/ml to early-to mid-log phase. The cells were then diluted in complete BSK-II media to a final cell density of 1×106 cells/mL, then incubated for 1.5 hours in 15% normal human serum (Complement Technology) or equivalent heat inactivated serum as a positive control for survival. Cell survival was assessed by dark field microscopy based on cell motility and membrane damage or lysis.