Time course cytotoxicity assays. A. HeLa, B. J774A.1, or C. A549 cells were infected with the indicated strains at a multiplicity of infection (MOI) of 50 in 12-well plates. Aliquots of culture supernatants were removed at the indicated times and lactate dehydrogenase (LDH) levels were measured as described in Materials and Methods. Complex I and complex IV strains are designated by blue or red lines, respectively. Due to repeated sampling of culture medium for LDH release assays, we consistently observe a slight increase in cytotoxicity measured in kinetic experiments vs. single time point assays as shown in Figure 1. The differences range from none to less than 20 %, depending on the cytotoxicity of the isolate. Error bars represent standard errors for measurements from at least three independent experiments.