Fig 2. Growth dynamics at the single cell level discriminates antibiotic tolerance from persistence in cellulo.
(A) Illustration of the in cellulo antibiotic survival assay in primary Bone Marrow Derived Macrophages (BMDM) infected with Salmonella. (B) CFU enumeration of WT or hisGP69L SL1344 Salmonella as well as WT or ΔhisG 14028 Salmonella in BMDMs treated with cefotaxime in the absence or presence of histidine in the infection medium. Data represent the mean and SD of at least three biological repeats. Data from the 48 h timepoint were compared using one way ANOVA with Tukey’s multiple-comparison test, ***p<0.001; NS, not significant. (C) Illustration of the fluorescence dilution assay to assess growth dynamics of a population at the single cell level. Growing cells dilute a pre-formed pool of mCherry at each cell division whereas the non-growing bacteria maintain high intensity fluorescence. (D) Representative flow cytometry profile of Salmonella 14028 grown in minimal medium for 4 h in the absence or presence of histidine for WT and ΔhisG strains. (E) Representative flow cytometry contour (left) and histogram (right) plots of bacteria extracted from BMDM after 16 h of gentamicin (- antibiotic condition) or 16 h of cefotaxime (+ antibiotic condition). G, growers and NG, non-growers.