The antibacterial activity of 29 different polyoxometalates (POMs) against Moraxella catarrhalis was investigated by determination of the minimum inhibitory concentration (MIC). The Preyssler type polyoxotungstate (POT) [NaP5W30O110]14- demonstrates the highest activity against M. catarrhalis (MIC = 1 μg/ml) among all tested POMs. Moreover, we show that the Dawson type based anions, [P2W18O62]6-, [(P2O7)Mo18O54]4-, [As2Mo18O62]6-, [H3P2W15V3O62]6-, and [AsW18O60]7- are selective on M. catarrhalis (MIC range of 2-8 μg/ml). Among the six tested Keggin type based POTs ([PW12O40]3-, [H2PCoW11O40]5-, [H2CoTiW11O40]6-, [SiW10O36]8-, [SbW9O33]9-, [AsW9O33]9-), only the mono-substituted [H2CoTiW11O40]6- showed MIC value comparable to those of the Dawson type group. Polyoxovanadates (POVs) and Anderson type POMs were inactive against M. catarrhalis within the tested concentration range (1-256 μg/ml). Four Dawson type POMs [P2W18O62]6-, [(P2O7)Mo18O54]4-, [As2Mo18O62]6-, [H3P2W15V3O62]6- and the Preyssler POT [NaP5W30O110]14- showed promising antibacterial activity against M. catarrhalis (MICs < 8 μg/ml) and were therefore tested against three additional bacteria, namely S. aureus, E. faecalis, and E. coli. The most potent antibacterial agent was [NaP5W30O110]14-, exhibiting the lowest MIC values of 16 μg/ml against S. aureus and 8 μg/ml against E. faecalis. The three most active compounds ([NaP5W30O110]14-, [P2W18O62]6-, and [H3P2W15V3O62]6-) show bacteriostatic effects in killing kinetics study against M. catarrhalis. We demonstrate, that POM activity is mainly depending on composition, shape, and size, but in the case of medium-size POTs (charge is more than -12 and number of addenda atoms is not being higher than 22) its activity correlates with the total net charge.
Keywords: Dawson archetype; Gram-negative pathogen; Preyssler archetype; bioactive polyoxometalates; metal-oxo clusters; minimum inhibitory concentration; time-killing analysis.