FIG. 1.

LDH release by J774A.1 cells infected with PA103 or mutants defective in type III secretion. Cells were infected for 3 h at an MOI of approximately 80. Mutants with defects in the type III secretion transcriptional activator (PA103exsA::Ω), the secretion apparatus (PA103pscJ::Tn5), or the translocation apparatus (PA103pcrG::Tn5) were noncytotoxic, whereas an exoU mutant (PA103exoU::Tn5) exhibited intermediate cytotoxic capacity. A plasmid (pAH807) containing an intact ExoU-encoding gene and its chaperone complemented the exoU mutant to a phenotype of full cytotoxicity. Error bars represent standard errors of the means for experiments performed in triplicate.