Effect of antagonists and agonists of natriuretic peptide receptors. (A) 2D black-and-white images resulting from CLSM observations of MPAO1 24-h biofilms obtained under static conditions after growth under control conditions and exposed to CNP (10−6 M), isatin (10−5 M) or both isatin and CNP. (B) COMSTAT analyses of biofilms of P. aeruginosa MPAO1 exposed to CNP, to isatin, or both to isatin and CNP. Data are means from three independent experiments for CNP exposure and two independent experiments for isatin and isatin-plus-CNP exposure. ***, P < 0.001; NS, not significantly different. (C) Cytotoxic activity of PA14 alone (control), PA14 exposed to the NPR-C agonist cANF4-23 (10−6 M), or PA14 exposed to the NPR-A agonist sANP (10−6 M). The cytotoxic effect of the bacterium was determined by measuring lactate dehydrogenase (LDH) accumulation in the medium. Data are the means for nine samples from three independent experiments for cANF4-23 and means for six samples from two independent experiments for sANP. ***, P < 0.001; **, P < 0.01; *, P < 0.05.