Cytotoxic activities of some Pseudomonas aeruginosa isolates: possible mechanisms and approaches for inhibition

Abstract

The cytotoxicity of 6 highly cytotoxic Pseudomonas aeruginosa isolates was tested against Vero cells. Cytotoxicity was found to be cell-associated, high cytotoxicity was observed at a multiplicity of infection of 200:1, and this activity gradually decreased as the bacterial count decreased. This cytotoxicity caused rounding and detachment of the Vero monolayer as early as 1 h after infection. Moreover, viable metabolically active bacteria were necessary for Vero cell killing. These results imply that one or more of the type III secretion system effector proteins (ExoU, ExoS, ExoT, or ExoY) were responsible for the observed cytotoxic effects. This cytotoxicity was affected by changes in pH and temperature and was associated with high adherence but poor invasion levels. The isolates P127, P139, P205, and P217 exhibited their cytotoxic effect within short infection periods (2 h), and MAFP (an ExoU inhibitor) caused a dose-dependent reduction of this effect, implying that these cytotoxicities were due to the effector ExoU. On the other hand, P206 and P231 caused loss of Vero cell viability only after prolonged incubation periods (10 h) and were unaffected by both MAFP and E216-5138 (ExoS inhibitor), indicating that ExoT may be the effector responsible for the observed cytotoxic effects. Several compounds were tested to inhibit bacterial cytotoxicity. Mannose of the tested antiadherents and poloxamer 407 of the tested pharmaceutical excipients had the greatest inhibitory effects. Concerning the metal ions, Fe3+ and Zn2+ nearly abolished the observed cytotoxic effects. © TÜBİTAK.