A SNS-032 Your Mates Is Talking About

, 2012). Nevertheless, by comparing the antimicrobial activity of SeNPs and TeNPs with silver nanoparticles (AgNPs), these latter generally show antimicrobial activity at lower concentrations than both SeNPs and TeNPs. In fact, AgNPs completely inhibited biofilm CDK inhibitor review formation in E. coli AB1157 and P. aeruginosa PAO1 at a concentration of 5 and 10 mg/L, respectively. However, the concentration required to eradicate an already formed biofilm structure is over 150 mg/L (Radzig et al., 2013), similar to the values reported in the present study for biogenic SeNPs and TeNPs. An unexpected finding in the present investigation is that both the biogenic SeNPs and TeNPs exhibited equivalent antimicrobial efficacy toward the bacterial cells grown either in plankonic form or in biofilm mode. This evidence is particularly significant since bacteria grown in biofilm form are reported to be more tolerant to antimicrobial agents, in particular to traditional antibiotics (Hall-Stoodley et al., 2004). On the basis of both the evaluation of antimicrobial activity and CLSM observations, it appears evident that SeNPs and TeNPs possess bactericidal properties. Anyway, the mechanisms responsible for the antimicrobial activity are not yet completely understood. One of the possible modes of action that has been proposed to explain the toxicity of other nanomaterials (AgNPs and ZnNPs) is the production of reactive oxygen species (ROS) (Manke et al., 2013). Reports already exist in the literature that attribute the antibacterial effects of different selenium compounds to the formation of free radicals (Tran et al., 2009). Moreover, selenium and tellurium oxyanions have also been found to trigger the generation of ROS, with both elements capable of reacting with intracellular thiols and forming intermediates that cause oxidative stress as a consequence of the formation of superoxide radicals (Zannoni et al., 2008). In the present study, after TeNPs exposition, the amount of ROS induced is lower than that recorded after tellurite exposure. On the other hand, we observed that SeNPs induce a higher production of ROS compared to selenite. However, we did not observe induction of ROS formation by SeNPs in a size-dependent manner. In fact, the amounts of ROS generated by different dimensional types of SeNPs were very similar, even if the toxicity effects they exert to the microbial populations increase with the lowest dimensions. Thus, even if reactive oxygen species are involved in the toxicity of NPs, there must be other mechanisms responsible for the antimicrobial activity of these nanostructured metals. For instance, it seems that nanoparticles can contribute to functional damages of cell membrane or wall by disrupting the integrity of these important envelopes (Pi et al., 2013). Some other mechanism related to the surface features of the nanoparticles may be involved however in conferring toxicity to NPs (Bao et al., 2015).