Antibacterial Activity of Ag 2 O/SrO/CaO Nanocomposite †

: The increase in bacterial resistance to one or several antibiotics has become a global health problem. Nanocomposites have become a tool against multidrug-resistant bacteria. A nanocomposite, Ag 2 O/SrO/CaO, was prepared from AgNO 3 , SrCl 2 · 6H 2 O, CaCl 2 , and a solution of Na 2 CO 3 via the calcination of the salts mixture. The nanocomposite was successfully prepared by the co-precipitation method and completely according to green chemistry, in terms of synthesis method, solvent and precursors. The nanocomposite was characterized by XRD, XRF, and FESEM analyses. Afterwards, the nanocomposite was applied for antibacterial activity against gram-positive and gram-negative bacteria including PS Aeruginosa, Keleb peneumonia, Staph coccus aureus, Staph sapropphyticus, and Escherichia coli.


Introduction
The mixture of metal oxide nanoparticles and the combination of two or more metal oxides has an improved set of properties.In this way, we can modify the physical, chemical, biological, and morphological properties of the oxides.The combination and calcination of metallic compounds can create diverse properties and applications in the product; for example, it is shown that silver compounds are severe against bacteria.
Metal oxides, especially CuO, NiO, CoO, ZnO, and Cu 2 O in their nano-forms, have been considered as potential biocide agents.Most of these metal oxides, and their antibacterial activity, have been often related to the production of reactive oxygen species (ROS) [1,2].
Metals and metal oxides show antibacterial properties in the following ways: protein dysfunction, production of ROS and antioxidant depletion, impaired membrane function, interference with nutrient uptake, and genotoxicity [1].

Peparation of Ag 2 O/SrO/CaO Nanocomposite
The Ag 2 O/SrO/CaO nanocomposite metal was prepared by the co-precipitation of corresponding carbonates from the aqueous solution of metal salts.Initially, 0.25 M, 30 mL solution of each of AgNO 3 (1.274g), SrCl 2 •6H 2 O (1.999 g), CaCl 2 (0.832 g), and a solution (1.00 M, 50 mL) of Na 2 CO 3 (5.299g) were prepared with distilled water.Next, AgNO 3 , SrCl 2 •6H 2 O, and CaCl 2 solutions were mixed, and the resulted mixture was stirred vigorously at room temperature for a few minutes.After this, the solution of 1.00 M Na 2 CO 3 was added slowly to the above mixture with agitation until the precipitation of the carbonates was complete.The final mixture was stirred for 4 h at 55-60 • C with constant stirring.Then, the white metallic precipitate was filtered and washed several times with distilled water.Then the produced compound was dried at room temperature.To obtain a multi-metal nanocomposite (Ag 2 O/SrO/CaO nanocomposite), the obtained dried precipitate was calcinated in a muffle furnace at 600 • C for five hours.As a result of the calcination, a metal oxide nanocomposite was formed from the carbonates [3].

Characterization
The XRD patterns of the title composite, shown in Figure 1, was applied for the investigation of crystalline structure of nanomaterials.In Figure 1, the 2θ peaks appear at 25.67  obtain a multi-metal nanocomposite (Ag2O/SrO/CaO nanocomposite), the obtained dried precipitate was calcinated in a muffle furnace at 600 °C for five hours.As a result of the calcination, a metal oxide nanocomposite was formed from the carbonates [3].

Antibacterial Activity
Antibacterial activity of the title nanocomposite against gram-positive an gram-negative bacteria were tested.The bacteria involve PS.Aeruginosa, Keleb pe neumonia, Staph coccus aureus, Staph sapropphyticus, and Esherichia.The results ar shown in Figure 3a-e and summarized in Table 2.It can be seen that the inhibition zon diameter from Ag2O/SrO/CaO is varied from 7.876 to 18.991 mm.

Antibacterial Activity
Antibacterial activity of the title nanocomposite against gram-positive and gramnegative bacteria were tested.The bacteria involve PS.Aeruginosa, Keleb peneumonia, Staph coccus aureus, Staph sapropphyticus, and Esherichia.The results are shown in Figure 3a-e and summarized in Table 2.It can be seen that the inhibition zone diameter from Ag 2 O/SrO/CaO is varied from 7.876 to 18.991 mm.

Antibacterial Activity
Antibacterial activity of the title nanocomposite against gram-positive and gram-negative bacteria were tested.The bacteria involve PS.Aeruginosa, Keleb peneumonia, Staph coccus aureus, Staph sapropphyticus, and Esherichia.The results are shown in Figure 3a-e and summarized in Table 2.It can be seen that the inhibition zone diameter from Ag2O/SrO/CaO is varied from 7.876 to 18.991 mm.Antibacterial effects of the nanocomposite may be through the following properties:  Antibacterial effects of the nanocomposite may be through the following properties: Cell membrane damage: Silver nanoparticles have physicochemical and biological properties that are different from the properties of silver in the from of bulk.In order to have toxic effects of silver nanoparticles, they must be able to interact with bacteria on the surface and even in the cytoplasm.Silver nanoparticles release silver ions that must be able to cross the bacteria cell membrane and this is not very easy.Bacteria are divided into two groups: gram-positive (layers of peptidoglycans) and gram-negative (layers of lipopolysaccharides).In both groups, silver ions must be able to cross the membrane.Silver nanoparticles have their first encounter with the outermost part of the membrane, which is composed of protein with electron donors include oxygen, phosphorus, nitrogen, and sulfur atoms.Thiol-containing agents can block silver nanoparticles and inhibit their antibacterial activity.In some papers, it is stated that silver nanoparticles are adsorbed on cell membranes and the accumulation of nanoparticles in bacterial membranes causes abnormal structure, gaps are created in the surface of the membrane, and the cell membrane is destroyed with the expansion of these cavities.Finally, the silver nanoparticles reach the cytoplasm and react with proteins, enzymes, and also DNA [4].
DNA interaction: The effect of silver Np on DNA was not understood in detail.Oxidative pressure was expressed as important mechanism proposed to damage DNA.Silver Np inhibit respiratory enzymes that conduct ROS formation.Silver ions react with bases in DNA with higher affinity than phosphate groups, although AgNp also have an antibacterial effect without releasing silver ions.AgNP can penetrate bacterial cells; AgNp invade the surface of cell membranes and disport permeability by modifying cell potential and by inhibiting cellular respiration.AgNp cations join to thiol groups in bacterial proteins, disrupting their activity.and causing cell death.The most important part of the mechanism of AgNp against bacterial DNA is oxidative stress [4].

Figure 3 .
Figure 3. Inhibition zones of different bacteria effected by the title nanocomposite.

Figure 3 .
Figure 3. Inhibition zones of different bacteria effected by the title nanocomposite.

Figure 3 .
Figure 3. Inhibition zones of different bacteria effected by the title nanocomposite.

Table 1 .
The XRF results as percentage of elements.

Table 1 .
The XRF results as percentage of elements.

Table 2 .
Inhibition zone diameters of different bacteria effected by the title nanocomposite.

Table 2 .
Inhibition zone diameters of different bacteria effected by the title nanocomposite.

Table 2 .
Inhibition zone diameters of different bacteria effected by the title nanocomposite.