Killing persisters with the synergy of l-serine. l-Serine accelerated the persister cell death rate in stationary phase when preformed persisters were treated. Experiments were performed in the presence of 5 mg/L ofloxacin (a) or 5 mg/L moxifloxacin (b) alone and in combination with 15 mM l-serine. (c) Percentage survival of E. coli persisters in the presence or absence of l-serine plus ofloxacin or moxifloxacin. Values were compared with the control (without l-serine) at the same antibiotic concentration. Data are shown as mean ± SD of triplicate wells. Similar results were obtained in three independent experiments. *P < 0.05. OFX, ofloxacin; MXF, moxifloxacin.