Increased survival of ampicillin exposure by E. coli strains deficient in genes identified by Tn-Seq. The ability to generate persister cells of mutant strains in the background CFT073 was assessed by CFU counting. Error bars denote standard errors corresponding to 3 independent trials. Statistical significance was determined using a two-tailed Student t test (*, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001). WT, wild-type strain.