Snapshots from live-cell imaging in deficient surfactant (DS) conditions at 4 days post-infection for (A) wild-type Mtb, (B) an attenuated ESX-1-deficient strain (esx-1), and (C) at 6 days post-infection for the avirulent Δicl1Δicl2 strain infected at a higher inoculum. The gene discussed is ESX1; the disease is infection.