Fluorescence microscopy was used to determine the state of E. coli before and after exposure to V. cholerae strains V52 and V52ΔvasK, where V. cholerae and E. coli were distinguishable by fluorescence at separate wavelengths. V. cholerae and E. coli were incubated on Luria–Bertani medium (LB) agar for 4 h, at which time bacteria were harvested, washed, fixed, and inspected by fluorescence microscopy. E. coli was visibly detectable before exposure to V52 or V52ΔvasK, but was completely absent from the field of view after 4 h of exposure to V52 (Fig. 3A). The loss of fluorescent signal is indicative of cell lysis as released mCherry would have been lost during the washing step following the incubation on LB-agar plates. The lysis of E. coli can be attributed to the T6SS because the V52ΔvasK treatment had no effect on the visualization of E. coli (Fig. 3B).