Pseudomonas aeruginosa
Time-lapse
Video Microscopy

Clinical isolates of P. aeruginosa are either invasive or cytotoxic based upon their interaction with epithelial cells. Invasive and cytotoxic strains of P. aeruginosa differ genotypically in some genes that are co-ordinately regulated by a transcriptional activator, ExsA. Both classes possess exoT, the gene encoding the 53-kDa form of exoenzyme S, yet only invasive strains have exoS, the gene encoding the 49-kDa form of exoenzyme S. However, only cytotoxic strains possess the gene encoding ExoU, a 70-kDa protein necessary for cytotoxic activity toward various types of epithelial cells. A fourth ExsA-regulated effector molecule, ExoY, has been identified in an invasive, but not a cytotoxic strain. ExsA-regulated exoproteins of P. aeruginosa are thought to be delivered via a type III secretion mechanism similar to that found in Yersinia spp. and some other gram-negative bacteria such as Salmonella and Shigella.

The differences in the interaction between a cytotoxic strain with epithelial cells and an invasive strain with epithelial cells are shown using time-lapse video microscopy.

Cytotoxic P. aeruginosa also kill macrophages, which are phagocytic cells important for normal defense aginst infection as well as during the resolution of infection. We used time-lapse video microscopy to investigate events associated with macrophage cell death and to study the role of some ExsA-regulated effector molecules in this death. The following movies show macrophages infected with cytotoxic P. aeruginosa PA103 and isogenic mutants lacking the regulator ExsA, or the effector molecules ExoU and/or ExoT.

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