(B) L. pneumophila bacteria lacking flaA or lqsA are impaired for spreading from amoebae. A. castellanii amoebae were infected (MOI 5, 52 h) with L. pneumophila JR32, ∆flaA or ∆lqsA harboring Ptac-mCherry-PflaA-gfp and embedded in 0.5% agarose/PYG medium. The fluorescence images are representative for the L. pneumophila strains indicated: JR32 (n = 25), ∆flaA (n = 13) or ∆lqsA (n = 19). Scale bars: 20 µm. 