Abstract
In a previous study, it was found that Keggin-structural polyoxotungstates such as undecatungsto-silicate ([SiW 1 1 O 3 9 ] 8 - , SiW 1 1 ) greatly sensitizes strains of methicillin-resistant Staphylococcus aureus (MRSA) to β-lactam antibiotics. Of the related tungsten compounds tested, undecatungsto-cobalto(II)silicate ([SiW 1 1 O 3 9 Co] 6 - , SiW 1 1 Co), which is one of the lacunary-substituted molecular species of SiW 1 1 , was found to have the strongest synergism with β-lactams. In this report, the effects of SiW 1 1 Co on the bacterial growth, the expression of penicillin-binding proteins (PBPs) and penicillinase (PCase) activity were studied to confirm the mechanism of action of SiW 1 1 Co. As a result, the suppressive effects of SiW 1 1 Co on the PBPs and PCase were stronger than those of SiW 1 1 , thereby more strongly sensitizing MRSA strains to β-lactams. The most suitable concentration of this compound for experiments appears to be 25-100μM, giving almost maximal synergism without severe growth retardation. Such a tungsten compound may be useful as a tool in laboratory tests for investigating resistant mechanisms.
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