Abstract
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) [NaP(5)W(30)O(110)](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, [P(2)W(18)O(62)](6-), [(P(2)O(7))Mo(18)O(54)](4-), [As(2)Mo(18)O(62)](6-), [H(3)P(2)W(15)V(3)O(62)](6-), and [AsW(18)O(60)](7-) are selective on M. catarrhalis (MIC range of 2-8 μg/ml). Among the six tested Keggin type based POTs ([PW(12)O(40)](3-), [H(2)PCoW(11)O(40)](5-), [H(2)CoTiW(11)O(40)](6-), [SiW(10)O(36)](8-), [SbW(9)O(33)](9-), [AsW(9)O(33)](9-)), only the mono-substituted [H(2)CoTiW(11)O(40)](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 [P(2)W(18)O(62)](6-), [(P(2)O(7))Mo(18)O(54)](4-), [As(2)Mo(18)O(62)](6-), [H(3)P(2)W(15)V(3)O(62)](6-) and the Preyssler POT [NaP(5)W(30)O(110)](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 [NaP(5)W(30)O(110)](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 ([NaP(5)W(30)O(110)](14-), [P(2)W(18)O(62)](6-), and [H(3)P(2)W(15)V(3)O(62)](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.