FIG 2.

Antibiotic screen revealing S. marcescens genes important for growth and survival. (A) Screen schematic. An input library (containing about 2 million insertion mutants) is grown to an optical density (OD) of 0.1 and divided between the following 4 conditions for an additional 6 h of growth: LB alone; LB plus cefoxitin 4 μg/ml; LB plus cefepime 0.025 μg/ml; and LB plus ciprofloxacin 0.05 μg/ml. (B) Under the screening conditions, the library without drug selection undergoes a more than 2-log expansion, while those with antibiotic decrease in CFU to a similar extent (about 0.5 log), with the library in cefoxitin undergoing expansion after 4 h, likely due to upregulation of AmpC beta-lactamase. Libraries were harvested for analysis at 6 h. (C) Number of genes with insertion mutants showing a ≥4-fold change at 6 h with a Mann-Whitney U P value of ≤ 0.01, compared to outgrowth in LB alone. All data are tabulated in Table S4 in the supplemental material. (D) Venn diagram illustrating genes showing coordinate enrichment or depletion. Individual genes comprising the depicted sets are tabulated in Table S5.