Fig. 3. A MK-deficient strain is incapable of aerobic respiration and, therefore, must generate energy via fermentation.

A. Proton motive force (PMF) was measured as the mean ratio of red:green fluorescence of WT and mutant strains of S. aureus grown to mid-exponential phase and incubated with 30 μM of the dye 3,3-diethyloxacarbocyanine iodide (DiOC₂). High levels of red fluorescence relative to green fluorescence indicate the presence of a PMF. Each PMF data set was generated from biological triplicates. B. D- and L-lactate production was measured in WT and SCV strains of S. aureus. Increased lactate production is indicative of an increase in the fermentation pathway. D- and L-lactate measurements were performed three times on three separate days. Additionally, technical triplicates were performed on each day.