Acid resistance of MG1655 with GSH and/or ciprofloxacin at a concentration of 10 mM GSH, 3 ng of ciprofloxacin/ml (subinhibitory concentration), and 10 mM GSH with 50 ng of ciprofloxacin/ml (inhibitory concentration). Acid resistance of MG1655 with GSH and/or ciprofloxacin at a concentration of 10 mM GSH, 3 ng of ciprofloxacin/ml (subinhibitory concentration), and 10 mM GSH with 50 ng of ciprofloxacin/ml (inhibitory concentration). Bacterial cells were grown to mid-log phase in LB broth (pH 7.0). Cells grown under the exposure conditions mentioned above were diluted 40-fold into LB broth (pH 3.0) and were incubated for 1 h at 37°C. Percent survival data represent ratios of counts of viable cells remaining after acid treatment to the viable counts before treatment. Initial cell densities (before exposure to the acidified medium) ranged from 4 × 107 to 2 × 108 CFU/ml. The results shown are averages from three independent experiments, with the SEMs indicated. Manish Goswami, and Akkipeddi Venkat Satya Surya Narayana Rao mSystems 2018; doi:10.1128/mSystems.00001-18