Figure 1. Ploidy impacts persistence to fluoroquinolones in stationary-phase populations.

(A) Persistence to LEVO is not influenced by staining with 5 μg/mL Hoechst 33342 (n = 4). (B) Cell sorting does not influence the persistence phenotype, where unsorted cells were diluted to the same density as sorted cells (n = 7). (C) Representative DNA histogram and gating strategy indicating the number of chromosomes in a stationary-phase population of wild-type E. coli stained with 5 μg/mL Hoechst 33342. (D) Cells sorted to contain 2Chr (as determined by Hoechst 33342 staining) are > 16 times as likely to be LEVO persisters than cells sorted to contain 1Chr (n = 7). Untreated samples demonstrate that any survival differences observed can be attributed to treatment with 5 μg/mL LEVO (n = 7). Statistical significance was initially determined using a one-way ANOVA (F(3,24) = 12.0, p < 0.0001) at the 5 h timepoint, because at that time point, persisters are the only remaining CFUs. Tukey HSD post-hoc test showed a significant difference at 5 h when comparing the means of 1Chr vs. 2Chr (p = 0.0003), 1Chr vs. ≥2Chr (p = 0.0001), and 1Chr vs. Total Sort (p = 0.0007). 1Chr, 2Chr, and >2Chr indicate chromosome number as determined by experiments presented in Figure 2. See also Figures S1 and S2. Representative gating strategy is indicated by a, b, and c. Error bars portray ± SEM. All replicates were independent biological replicates. * indicates statistical significance.