Polyoxometalates are a well-known group of anionic polynuclear metal oxides presenting important therapeutic potential as anticancer, antiviral, and antibacterial agents [1]. In a previous work [2], we measured the minimum inhibitory concentrations (MIC) of 3 polyoxovanadates (POVs), namely V10, MnV11 and MnV13 against the Gram-negative bacteria Escherichia coli. MICs were obtained following the well-accepted serial two-fold dilution method, which requires a 16-20h culture and might neglect the effects of compounds’ metabolism/speciation changes during the incubation.
In this work, we further studied the antibacterial action of those POVs against the gram-positive Enterococcus faecalis by monitoring the growth of the microorganism at different incubation times.
The compounds were tested at 0.5 mM concentration, based on previous data [2], and growth curves of the bacteria were obtained from the optical density of the cultures at 600 nm. In addition, the MICs of these POVs against E. faecalis were determined for the first time.
The comparison between the growth curves in the presence of the POVs and the corresponding control cultures indicated that the compounds did not affect the lag time of the culture. However, the inhibitory effects of V10, MnV11 and MnV13 on the growth of E. faecalis were evident right from the beginning of the exponential phase. The monomeric species of vanadate (V1) showed only modest inhibition of bacterial growth. Notably, the inhibition data obtained until 7h culture was sufficient to identify the POVs with stronger antibacterial activity, V10, MnV11 and MnV13, in agreement with the results of MIC determination at 18h. Putting it all together, the results point out that automatized monitoring of the growth curve can meet the need for rapid methods to screen antibacterial POVs against different bacteria.
[1] Aureliano et al. (2021) Coordination Chemistry Reviews, 447, 214143.
[2] Marques-da-Silva et al. (2019) New Journal of Chemistry, 43, 17577.
