PARP1 and infection: HeLa cells were infected at a multiplicity of infection (MOI) of 10 with isogenic mutants of the PA103 strain, a clinical isolate which encodes and expresses ExoU and ExoT [24,25], including PA103∆exoU (∆U) which carries an in-frame deletion in the exoU gene but expresses ExoT; PA103∆exoU/exoT(R149K) (∆U/T(G-A+)) which carries an in-frame deletion in the exoU gene but expresses ExoT with a mutant GAP but functional ADPRT domain; or PA103 pscJ::gentR (T3SS mutant, unable to deliver ExoT into host cells) (S1 Table).