# Antibacterial Activity of Green Synthesised Silver Nanoparticles on _Saccharomyces cerevisiae_
## 3 Results and Discussion
Analysing the results obtained by subculturing samples of yeast extract with bacterial strains, the cells of the clinical strain _K. pneumoniae_ 520 remained adhered at the level of the control cells (Figure 5). A slight decrease in the number of adhered cells compared with the control was observed in the sample with 0.5 mM AgNO\({}_{3}\), but this value was still within 97%. This means that the obtained samples of colloidal solutions of silver could reduce the metabolic activity of _K. pneumoniae_ 520, but the percentage of attached cells remained high. In this case, the use of such a colloidal solution could not be said to be effective against strain _K. pneumoniae_ 520. Samples of yeast extract to which AgNO\({}_{3}\) was added at a concentration of 0.5 mM could increase the adhesion of _S. aureus_ ATCC 25923 cells, but at higher concentrations, cell adhesion almost did not take place. This correlated with previous results, thus the samples with concentrations of 1.0 mM, 1.5 mM, and 2.0 mM AgNO\({}_{3}\) demonstrated effective action against _S. aureus_ ATCC 25923 (Figure 5). Cells of _E. coli_ strain ATCC 25922 lost their adhesiveness when using yeast extracts with the addition of AgNO\({}_{3}\) at concentrations of 1.5 mM and 2.0 mM. Using the same samples in the study of metabolic activity, these cells also had low metabolic activity. The most effective use of silver-containing yeast extract was against the adhesion of _S. aureus_ 1536 cells. The effective concentrations were 1.0 mM, 1.5 mM and 2.0 mM, which fully corresponded with the results obtained in the study of metabolic activity. The best results were obtained when studying the effect on the adhesion of bacterial strains using samples of the supernatant. The culture of _K. pneumoniae_ 520 significantly lost adhesion in all studied samples. Compared with the results of metabolic activity, the most effective samples were those with concentrations of 1.0 mM, 1.5 mM and 2.0 mM AgNO\({}_{3}\) (Figure 6). These samples effectively reduced the adhesion of cultures of _S. aureus_ 1536 and _S. aureus_ ATCC 25923, which correlated with the results obtained in the MTT test. Figure 5: Value of adhered cells after subculturing with yeast extract (crystal violet). 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\({}_{3}\)\({}^{*}p<0.05\). The culture of _E. coli_ ATCC 25922 lost the ability to adhere only when using samples with the addition of 1.5 mM and 2.0 mM AgNO\({}_{3}\), while the decrease in metabolic activity was detected in the sample using 1.0 mM AgNO\({}_{3}\) (Figure 6). Biogenic synthesis of nanoparticles is carried out on a range of objects. However, the range of antibacterial activity was quite similar for all nanoparticles obtained by green synthesis. For example, nanoparticles synthesised from _Pimpinella anisum_ seed extract had antimicrobial activity against _Staphylococcus pyogenes_, _Acinetobacter baumannii_, _Klebsiella pneumoniae_, _Salmonella typhi_ and _Pseudomonas aeruginosa_[15]. Another study described the biogenic synthesis of AgNP using a commercial extract of green tea (_Camellia sinensis_). The synthesised nanoparticles had antibacterial activity against _Staphylococcus aureus_, _P. aeruginosa_, _K. pneumoniae_, _Escherichia coli_ and _Salmonella enterica_[16]. An attempt to use pomerangate peel (_Punica granatum_) as a model for the synthesis of silver nanoparticles has also been described, with the synthesised nanoparticles showing high antimicrobial activity on _E. coli_, _P. aeruginosa_, _Proteus vulgaris_, _S. aureus_, _Staphylococcus epidermidis_ and _K. pneumoniae_[17]. Nanoparticles synthesised on _Pichia kudriavzewii_ HA-NY2 and _Saccharomyces uvarum_ HA-NY3 showed significant inhibitory activity against _Bacillus subtilis_, _S. aureus_, _Pseudomonas aeruginosa_ and _Candida tropicalis_[18].