Pseudomonas aeruginosa cytotoxin: periplasmic localization and inhibition of macrophages.

Pseudomonas aeruginosa cytotoxin has been isolated previously from cell autolysates. Both purified cytotoxin and periplasmic contents (osmotic shock fluid) cross-reacted on Western immunoblots with antibodies specific for cytotoxin. In addition, both preparations caused a significant reduction in antibody-mediated phagocytosis of P. aeruginosa M2 by mouse macrophage cell line P388D1. Phagocytosis was restored in each case on preincubation of cytotoxin or periplasmic contents with anti-cytotoxin serum. Both cytotoxin and periplasmic contents caused depolarization of the P388D1 cell membrane, as demonstrated with a polarization-sensitive fluorescent probe. Similar correlations were not observed for other P. aeruginosa cell fractions or for osmotic shock fluid from Escherichia coli C600. These data indicate that P. aeruginosa cytotoxin is localized in the periplasm and has the potential to inhibit macrophage-mediated phagocytosis, possibly by perturbing ion gradients across the macrophage plasma membrane.