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

Abstract

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 β subunit in F1.

Fig. 1

The effect of dioctyl sodium sulfosuccinate (DSS) alone and together with Ag nanoparticles on E. hirae ATCC9790 and E. coli K-12 lag phase duration. Control was bacterial growth without nanoparticles. Ag nanoparticles and DSS were diluted by 10, 20, 50, 100, 200 and 500 folds. For details see “Methods”

Fig. 2

The effect of dioctyl sodium sulfosuccinate (DSS) alone and together with Ag nanoparticles E. hirae ATCC9790 and E. coli K-12 specific growth rate. For details see “Methods”

Fig. 3

Changes in ATPase activity of membrane vesicles of E. hirae in the presence of Ag nanoparticles and DSS in K⁺-containing medium. For details, see “Methods”

Fig. 4

Proposed scheme for Ag nanoparticles effects on bacteria. Ag nanoparticles are suggested to affect H⁺-coupled membrane transport of bacteria. E. coli and E. hirae possessed H⁺–K⁺ exchange through F_OF₁ and K⁺-transport system (left side). In the case of E. hirae Ag nanoparticles changed the stoichiometry of H⁺–K⁺ exchange through membrane. The effect on F_OF₁ and disturbance of the interaction between F_OF₁ and K⁺-transport system (right side) might be responsible for stronger antibacterial effects with E. hirae

Fig. 5

Ag nanoparticles distribution in the colloid solution depending on their size. For source of Ag nanoparticles, see “Methods”