Effects of various heavy metal nanoparticles on Enterococcus hirae and Escherichia coli growth and proton-coupled membrane transport

Background: Due to bacterial resistance to antibiotics there is a need for new antimicrobial agents. In this respect nanoparticles can be used as they have expressed antibacterial activity simultaneously being more reactive compared to their bulk material. The action of zinc (II), titanium (IV), copper (II) and (I) oxides thin films with nanostructured surface and silver nanoscale particles on Enterococcus hirae and Escherichia coli growth and membrane activity was studied by using microbiological, potentiometric and spectrophotometric methods. Results: It was revealed that sapphire base plates with deposited ZnO, TiO2, CuO and Cu2O nanoparticles had no effects neither on E. hirae nor E. coli growth both on agar plates and in liquid medium. Concentrated Ag nanoparticles colloid solution markedly affected bacterial growth which was expressed by changing growth properties. E. hirae was able to grow only at < 1:200 dilutions of Ag nanoparticles while E. coli grew even at 1:10 dilution. At the same time Ag nanoparticles directly affected membranes, as the FOF1-ATPase activity and H+-coupled transport was changed either (E. coli were less susceptible to nanoparticles compared to E. hirae). Ag nanoparticles increased H+ and K+ transport even in the presence of N, N'-dicyclohexylcarbodiimide (DCCD), inhibitor of FOF1. The stoichiometry of DCCD-inhibited ion fluxes was disturbed. Conclusions: These results point out to distinguishing antibacterial effects of Ag nanoparticles on different bacteria; the difference between effects can be explained by peculiarities in bacterial membrane structure and properties. H+-K+-exchange disturbance by Ag nanoparticles might be involved in antibacterial effects on E. hirae. The role of FOF1 in antibacterial action of Ag nanoparticles was shown using atpD mutant lacked beta subunit in F-1.