Figure 3: Growth-inhibition profiles of bacteriolytic antibiotics.

(a,b) Plate reader assay sets in duplicates of S. pneumoniae D-PEP22 cells treated with a concentration series of ampicillin (AMP) (a) and cephalexin (LEX; b) measuring cell density (closed symbols) and gene expression (symbols without outline). Experiments were replicated at least three times. (c–f) Still images (phase contrast) after 1, 2, 3, 5 and 10 h of incubation of D-PEP22 cells growing on a semisolid surface containing 0.01 μg ml⁻¹ ampicillin (c), 0.015 μg ml⁻¹ ampicillin (d), 0.83 μg ml⁻¹ cephalexin (e, arrows point to a cell developing the HRP) and the HRP of D-PEP22 also growing in the presence of 0.83 μg ml⁻¹ cephalexin (f). Scale bar, 5 μm.