Synthesis, characterization and in vitro antibacterial mechanism study of two Keggin-type polyoxometalates

In this article, two Keggin-type polyoxometalates [Co(L)₂]₃[PMo₁₂O₄₀] (1) and [Co(L)₂]₃[PW₁₂O₄₀] (2) (HL = 2-acetylpyrazine thiosemicarbazone) were prepared and fully characterized. The compounds are stable in aqueous solution with different pH values and show superior antibacterial activity against Escherichia coli (E. coli: minimal inhibitory concentration (MIC) = 0.00375, 0.12 μg/mL), Agrobacterium tumefaciens (A. tumefaciens: MIC = 0.06, 0.12 μg/mL), Bacillus subtilis (B. subtilis: MIC = 0.015, 0.06 μg/mL) and especially for Staphylococcus aureus (S. aureus: MIC = 0.00048, 0.015 μg/mL) for 1 and 2, respectively. The time kill studies showed the entire killing of specific bacteria during 4 to 8 h. In addition, the possible antibacterial mechanism of compound 1 was explored systematically. The experimental results proved that cell wall/membrane damage, leakage of protein, inhibition of respiratory chain dehydrogenases activity, enhancement of intracellular reactive oxygen species (ROS) and depletion of glutathione (GSH) were the potential causes of bacteria death.