Measurement of bacterial oxygen consumption.

S. Typhimurium strains grown overnight in LB broth were diluted 1:200 in LB broth and grown at 37°C with shaking until the OD₆₀₀ value reached 0.4. The cultures were then transferred into a multiport measurement chamber (model NOCHM-4; WPI Inc., USA) equipped with an Iso-Oxy-2 O₂ probe connected to a free-radical analyzer (model TBR4100; WPI Inc.) at 37°C. The data were collected using the Labchart program (WPI Inc.). The remaining O₂ concentrations in the cultures were recorded over time, and, when necessary, the cultures were treated for 1 min with β-mercaptoethanol (10 mM) or spermine NONOate (50 μM) before measurement. The data were calculated as molar concentrations of O₂ and graphed as the O₂ concentration as a percentage of the O₂ concentration recorded when the measurement started (time zero [t₀]).