# Review on Silver Nanoparticles as a Novel Class of Antibacterial Solutions
## 4 Silver Nanoparticles and Their Antibacterial Role
### Antibacterial Activity of Silver Nanoparticles
Due to this increasing resistance to drugs, researchers had to look for alternatives that would allow them to surpass this resistance without side effects. Bacteria have developed various mechanisms to fight against antibiotics such as: cell through efflux pumps, inactivation of antibiotics, and alteration to metabolic pathway [65]. We reviewed over 60 articles that studied silver nanoparticles. Along the study, we have depicted the multiple methods used for silver nanoparticles synthesis and the substances used in this process. Depending on the method and substances, the resulting nanoparticles have different characteristics which have a different antibacterial activity. We focused on searching relevant data on the antibacterial activity of silver nanoparticles on _Staphylococcus aureus_ and _Escherichia coli_. We have identified multiple articles that used \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Size (nm)**} & \multirow{2}{*}{**Used Substances**} & \multirow{2}{*}{**Shape**} & **MIC _S. aureus_ & **MIC _E. coli_ & \multirow{2}{*}{**Ref**} \\  & & & **(\(\mu\)g/mL)** & & **(\(\mu\)g/mL)** & \\ \hline
23 \(\pm\) 2 & Silver nitrate, air borne fungus & Pentagonal & 9.23 & 5.063 & [13] \\
70.4 \(\pm\) 0.4 & Silver nitrate, gum arabic, ascorbic acid, sodium hydroxide & Spherical & 430 & 400 & [56] \\
16 \(\pm\) 2 & Silver nitrate, ethanol, sodium hydroxide, polyvinyl pyrrolidone & Spherical & & 35 ppm & [61] \\
20–30 & Silver nitrate, ethanol, fenugreek & Spherical & 12.5 & 6.25 & [17] \\
9–11 & Silver nitrate, Chlorella vulgaris & Spherical & 50 & & [62] \\
4–15 & Silver nitrate, fenugreek extract & Spherical & 10 & 25 & [63] \\
15 \(\pm\) 7.6 & Silver nitrate, glucose, genomic DNA & Spherical & 250 & 250 & [58] \\
15–20 & Silver nitrate, aqueous rhizome extract & Cubical & & 25 & [51] \\  & Silver nitrate, sodium bis(2-ethylhexyl) & & & & \\
20–70 & sulfosuccinate (AOT), ascorbic acid (molar ratio of water to AOT of 3–15) & & & & \\
125 & Silver nitrate, AOT, ascorbic acid (molar ratio of water to AOT of 25) & Nanowires & 32 & 32 & [11] \\
10–20 & Silver nitrate, sodium borohydride, polyvinylpyrrolidone & Spherical & \(14.7\pm 1.19\) & & [48] \\
15 \(\pm\) 5 & Silver nitrate, sodium citrate, sodium borohydride, cotton cellulose whiskers & Spherical & 14.2 & 7.1 & [16] \\  & Silver nitrate, N-Hydroxy succinimide, Thioglycolic acid, 1-3 diethylamino & & & \\
16–25 & propyl-e ethyl carbonidine hydrochloride, & Spherical & 0.8 & 1.6 & [2] \\  & 3 N-Morpholinopropanesulfonic acid, sodium borohydride & & & \\
20 & Silver nitrate, silica, polystyrene & Spherical & 75 & 50 & [59] \\
20–40 & Silver nitrate, chondro sulfate scaffolds & Spherical & & 6.2 & [24] \\
3 & Solid silver, nitric acid, sodium chloride & Spherical & & 2 & [64] \\  & Silver nitrate, L-cysteine, & & & \\
55 & cetyltrimethylammonium bromide, polyvinyl alcohol & & & \\
53 & Silver nitrate, citric acid, zinc nitrate & Spherical & 60 & 550 & [32] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: MIC results on _S. aureus_ and _E. coli_ of silver nanoparticles obtained with chemical methods. the inhibition zones and minimal inhibitory concentration to determine the success of using silver nanoparticles against these bacteria. In our analysis, we divided the silver nanoparticles based on their obtaining method and then assessed the ZOI and MIC against _S. aureus_ and _E. coli._ Our study may provide support for selection of design, synthesis methods and antibacterial analytical methods in accordance to intended antibacterial application.