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Richard Bach

mendel

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Oxidative Stress in Staphylococcus aureus Treated with Silver(I) Ions Revealed by Spectrometric and Voltammetric Assays

The bacterial growth is greatly inhibited due to silver(I) ions [1,2]. Silver(I) ions are stored in vacuoles and cell walls as granules inhibiting cell division, interacting with nucleic acids [3] and thiol groups in enzymes and proteins essentials for the vital cell functions [4]. For these reason, the silver(I) ions are used to control bacterial growth in medical and non-medical applications [1,5-7]. The mechanism of action of silver(I) ions are inactivation of membrane proteins, interference with electron transport system and inhibition of respiratory enzymes to promote the generation of reactive oxygen species, especially superoxide-radical, and consequent bactericidal activity [2,8]. The silver nanoparticles have been also applied as antimicrobial agents. These particles have a low toxicity to human cells, and a far lesser probability to cause microorganism resistance than other antibiotics [9]. Silver nanoparticles reduce the expression of some enzymes and inhibiting respiratory chain. When silver nanoparticles enter into bacteria cells, they condense DNA to prevent DNA from replicating and cells from reproducing [6]. Under aerobic conditions silver(I) ions exhibit higher bactericidal activity against Staphylococcus aureus, a model strains for gram positive bacteria.

Oxidative stress is one of the markers, which enables monitoring of toxic effects of generally heavy metals including silver(I) ions on microorganisms [2,10]. This toxic effect is based on the binding of silver(I) ions to the bacterial cell wall and membranes, which leads to inhibition of the respiratory process [6,11,12]. Due to ability of silver(I) ions to induce excessive production of ROS that affect almost all biomolecules, they are also able to cause metabolic toxicity. Organisms have the protective mechanisms that can effectively eliminate formed free radicals and thus eliminate their toxic effects [2,13]. On the other hand, these protective mechanisms have limited capabilities based on the proteosynthetic and generally biosynthetic abilities. Moreover, excess of ROS enables the monitoring of oxidative stress based on determination of antioxidant capacity [14,15]. Numerous methods for determination of antioxidant activity have been developed in the field of chemical analysis and biological evaluation of antioxidant characteristics [16-29]. Their diversity is given by the fact that low molecular weight antioxidants may act by different mechanisms, most often by the direct reaction with free radicals (quenching, trapping). A more precise definition of the chemical mechanism of their effect is often issue. Therefore, the procedures evaluating the antioxidant activity are based on chemically different principles [27,29,30]. Spectrophotometric methods are the most used methods in the determination of antioxidant activity/capacity. We studied oxidative stress in S. aureus extracts influenced by silver ions and hydrogen peroxide. In our study for the measurement of oxidative stress we used two different methods– ABTS (2.2´-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)) and DPPH (2.2-diphenyl-1-picrylhydrazyl). By these methods we determined the amount of radicals in S. aureus lysates. The results of spectrophotometric studies were completed with electrochemical analysis. Oxidative stress in S.aureus lysates was also studied by cyclic voltammetry using printed electrode and flow cell.

Podpořeno projekty: SIX CZ.1.05/2.1.00/03.0072

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