Killing of B. burgdorferi with drug combinations. (a) Time-dependent killing of late exponential B. burgdorferi cultures exposed to the indicated antibiotics in combination. Amoxicillin (Amox) (6 μg/ml), ceftriaxone (Cef) (3 μg/ml), and doxycycline (Dox) (2.5 μg/ml) (n = 6). (b) Killing of late exponential B. burgdorferi exposed to gemifloxacin (Gemi) (1.5 μg/ml) and/or spectinomycin (Spec) (160 μg/ml) singly or in combination (n = 6). An aliquot was taken at indicated time points, washed, diluted, and plated on semisolid BSK-II medium for CFU counts. Error bars represent standard errors.