# Review on Silver Nanoparticles as a Novel Class of Antibacterial Solutions
## 4 Silver Nanoparticles and Their Antibacterial Role
### Antibacterial Activity of Silver Nanoparticles  
Different results were reported by various studies concerning the _Staphylococcus aureus_ and _Escherichia coli_ antimicrobial effects. In the following table, the correlation between nanoparticle size and the obtained MIC values is presented (Table 3) [56]. Figure 4: Antibiotic conjugation with nanoparticles. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Size (nm)**} & \multirow{2}{*}{
\begin{tabular}{c} **Synthesis** \\ **Method** \\ \end{tabular} } & \multirow{2}{*}{**Substances Used in Synthesis**} & \multirow{2}{*}{**Shape**} & \multirow{2}{*}{**ZOI _S. aureus_**} & \multirow{2}{*}{**ZOI _E. coli_**} & \multirow{2}{*}{**Ref.**} \\ \cline{5-5}  & & Silver nitrate, chloroquine acid, Hex & & & \\ \hline
23 & Green & chloroplatinic acid, rind extract of & Spherical & \(12\pm 3\) & & [8,57] \\  & & garcinia mangostana & & & \\
20–30 & Green & Silver nitrate, ethanol, fenugreek & & & \\
20–30 & Green & & leaf extract & & \\
15 \(\pm\) 7.6 & Green & Silver nitrate, glucose, genomic DNA & Spherical & \(7.03\pm 0.5\) & & [58] \\
15–20 & Green & Silver nitrate, aqueous rhizome & & & \\
15–20 & Green & & extract of copifscinesis & & \(12\pm 1.2\) & [51] \\
18.94 & Green & Silver nitrate, aqueous extract of & & & \\
15–30 & Green & & chlorella vulgaris & & \\
60–110 & Green & Silver nitrate, extract of sumac fruits & Spherical & & \\  & & Silver nitrate, sodium chloride, & & & \\
60–110 & Green & & hydrochloric acid, sodium & Hexagonal & 13 & [9] \\  & & & hydroxide, pH 5 & & \\
10–40 & Green & & hydrochloric acid, sodium & Spherical & & \\  & & hydroxide, pH 9 & & & \\
20 & Chemical & Silver nitrate, silica, polystyrene & Spherical & 12.1 & 13.5 & [59] \\
30–80 & Chemical & Silver nitrate, trisodium citrate & Spherical & & 1 & [10] \\  & & Silver nitrate, polyvinyl pyrrolidone, & & & \\
150 & Chemical & trisodium citrate, hydrogen peroxide, & & & \\  & & sodium borohydride & & & \\
25–70 & Chemical & Silver nitrate, sodium borohydride & & & \\
15–50 & Chemical & & Silver nitrate, trisodium citrate, & & \\  & & sodium borohydride & & & \\
30–200 & Chemical & & trisodium citrate, hydrogen peroxide, & & \\  & & sodium borohydride, performed in a & & \\  & & Silver nitrate, sodium hydroxide, & & & \\  & & diamime tetra acetic acid, ethylene & & \\
10–100 & Chemical & tetrazolium bromide, 3-4-5-diphenyl- & & & \\  & & 2-thiazoloyl-2-5-diphenyl & & & \\  & & 2h trypsin & & & \\  & & Silver nitrate, L-cysteine, & & \\
55 & Chemical & cetyltrimethylammonium bromide, & & & \\  & & polyvinyl alcohol & & & \\
14–42 & Chemical & Silver nitrate, peptone, beef and yeast & & & \\  & & extract, sodium chloride & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: ZOI results on _S. aureus_ and _E. coli_ of silver nanoparticles. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{2}{c}{**Nanoparticle Size**} & \multicolumn{2}{c}{**MIC (ug/mL) on**} & \\
**(Nanometers)** & _Staphylococcus aureus_** & **MIC (ug/mL) on _E. coli_** \\ \hline
4 & 13.5 & 6.75 \\
10 & 50 & - \\
5–20 & 53 & 27 \\
30 & 20–80 & 80–320 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Correlation between nanoparticles’ size and MIC in _S. aureus_ and _E. coli_ cultures. Similarly, the table below reveals the MIC values obtained for various synthesis methods, shape and dimensions of nanoparticles regarding their effect against _S. aureus_ and _E. coli_ (see Table 5). The previous two tables show the antibacterial activity of silver nanoparticles using the MIC test. Regarding the ZOI test, we can observe a connection between their size and shape and the obtained MIC values. One of the most difficult challenges for researchers is the increasing resistance to antibiotics of bacteria such as _Staphylococcus aureus_, _Enterococcusecium_, _Escherichia coli_, _Pseudomonas aeruginosa_, _Klebsiella pneumoniae_, and _Enterobacter_ species.