# Antibacterial Activity of Green Synthesised Silver Nanoparticles on _Saccharomyces cerevisiae_
## 3 Results and Discussion
The concentration of silver ions in the samples of yeast lysate and supernatant with 0.5 mm AgNO\({}_{3}\) was found not to be significantly different (\(p=0.77\)), i.e., both the yeast extract and the supernatant contained the same amount of silver ions. The same could be said of the samples where the 1.0 mM concentration of AgNO\({}_{3}\) was introduced. However, in this case, there was no significant difference between the concentration of silver ions in the supernatant and the yeast lysate since \(p=0.07\). In samples where AgNO\({}_{3}\) concentrations of 1.5 mM and 2.0 mM were applied, there were higher concentrations of silver ions in the yeast lysate than in the supernatant (\(p=0.01\) and \(p=0.03\) respectively): 1.75 [1.33; 3.33] and 1.45 [1.07; 1.55] times higher respectively. The results obtained indicated that at concentrations of 0.5 mM and 1.0 mM, there was no difference in the accumulation of silver ions in different types of samples of yeast lysate and supernatant. Only at high concentrations (1.5 mM and 2.0 mM) could a significant difference be observed. The last stage of the study was to establish the antibacterial properties of the samples. After 24 h of incubation of test bacterial cultures with yeast lysate samples, there was a significant decrease in the metabolic activity of cells of strains of _S. aureus_ ATCC 25923, _S. aureus_ 1536 and _K. pneumoniae_ 520 for samples with concentrations of 1.0 mM, 1.5 mM and 2.0 mM. Decreased metabolic activity of _E. coli_ ATCC 25922 cells was observed in only two concentrations: 1.5 mM and 2.0 mM (Figure 3). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Concentration of Silver Ions, mM**} \\ \hline
**AgNO\({}_{3}\), mM \({}^{**}\)** & **Sterile dH\({}_{2}\)O** & **0.5** & **1.0** & **1.5** & **2.0** \\ \hline Supernatant & \(-0.01\) [\(-0.01\); 0.00] & 0.03 [0.01; 0.03] & 0.05 [0.03; 0.06] & 0.04 [0.03; 0.08] \({}^{*}\) & 0.11 [0.11; 0.14] \({}^{*}\) \\ \hline Lysate & 0.01 [0.01; 0.01] & 0.02 [0.02;0.03] & 0.04 [0.04; 0.04] & 0.07 [0.06; 0.10] \({}^{*}\) & 0.16 [0.15; 0.17] \({}^{*}\) \\ \hline \hline \end{tabular} \({}^{*}\)_p\(<0.05\). \({}^{**}\) The concentration of ArNO\({}_{3}\) added to the _S. cerevisiae_ 71B culture medium.  
\end{table} 
Table 1: Final concentration of silver ions in the sample solution. The average cell survival in toxic samples of yeast lysate was about 10%. An interesting fact is that there was a sharp decrease in the metabolic activity of cells without a smooth transition. Furthermore, it should be noted that the antibacterial effect of yeast lysates with silver ions was generally higher for clinical isolates, which is a positive result. When studying the antibacterial action of the supernatant samples, an interesting fact was established. Samples to which 0.5 mM AgNO\({}_{3}\) was added showed a significant increase in metabolic activity after 24 h of incubation (Figure 4). Such results were obtained on cultures of _E. coli_ ATCC 25922 and _S. aureus_ 1536. At the same time, for all studied bacterial cultures, an antibacterial effect of supernatant samples to which silver nitrate was added at concentrations of 1.0 mM, 1.5 mM and 2.0 mM (Figure 4) was shown. Figure 4: Bacterial cell survival after subculturing with supernatant by MTT test. The yeast extracts were obtained from samples of yeast _S. cerevisiae_ 71B, cultured in 20% glucose solution with the addition of: (1) sterile dH\({}_{2}\)O, (2) 0.5 mM AgNO\({}_{3}\), (3) 1.0 mM AgNO\({}_{3}\), (4) 1.5 mM AgNO\({}_{3}\) and (5) 2.0 mM AgNO\({}_{3}\) * \(p<0.05\). Figure 3: Bacterial cell survival after subculturing with yeast extract by MTT test. The yeast extracts were obtained from samples of yeast _S. cerevisiae_ 71B, cultured in 20% glucose solution with the addition of: (1) sterile dH\({}_{2}\)O, (2) 0.5 mM AgNO\({}_{3}\), (3) 1.0 mM ANO\({}_{3}\), (4) 1.5 mM AgNO\({}_{3}\) and (5) 2.0 mM AgNO\({}_{3}\) * \(p<0.05\). Quite different results were obtained by studying the number of adhered cells.