E. coli CFT073 and E. coli MG1655 persistence. E. coli CFT073 and E. coli MG1655 persistence. Cultures were grown overnight in 0.4% glucose M9 minimal medium as described in Materials and Methods. Persister cell assays were performed as described in Materials and Methods. ▲, E. coli CFT073; ●, E. coli CFT073 plus ampicillin; ♦, E. coli MG1655; ■, E. coli MG1655 plus ampicillin. Bars representing standard errors of the means of counts from 2 independent experiments are presented for each time point. At 24 h, the approximately 1,000-fold difference between the counts of E. coli CFT073 persisters and E. coli MG1655 persisters in the presence of ampicillin is statistically significant (P = 0.0052). Mary P. Leatham-Jensen et al. mSphere 2016; doi:10.1128/mSphere.00055-15