## 3 Results and Discussion
### bAuNPs and Ampicillin Effect on Bacterial Growth and Viability
Several studies have explored the use of AuNPs to deliver antibiotics, and these investigations support the notion that the effectiveness of antibiotics remains unchanged when attached to AuNPs [36; 37; 38; 39]. The conjugation of antibiotics with AuNPs offers the potential for enhanced therapeutic outcomes and improved drug delivery to target bacterial infections. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Agent** & **Growth Condition** & **CFU/mL** \\ \hline \multirow{4}{*}{MSSA} & NC & \(3.93\times 10^{8}\) \\ \cline{2-3}  & 0.001 mg/L Amp & \(3.40\times 10^{8}\) \\ \cline{2-3}  & 0.1 mM bAuNPs & \(2.00\times 10^{8}\) \\ \cline{2-3}  & Both & \(1.05\times 10^{8}\) \\ \hline \multirow{4}{*}{MRSA} & NC & \(4.40\times 10^{8}\) \\ \cline{2-3}  & 0.001 mg/L Amp & \(3.85\times 10^{8}\) \\ \cline{2-3}  & 0.1 mM bAuNPs & \(2.63\times 10^{8}\) \\ \cline{2-3}  & Both & \(1.48\times 10^{8}\) \\ \hline \end{tabular} Legend: NC—normal condition, i.e, basal medium only; Amp—ampicillin; bAuNPs—biosynthetic gold nanoparticles; MSSA—Methicillin-susceptible _S. aureus_; MRSA—Methicillin-resistant 5. _anevus_; CFU—colony-forming units.  
\end{table} 
Table 1: Effect of ampicillin and bAuNPs in MSSA and MRSA viability. Figure 5: Effect of specific concentrations of ampicillin and bAuNPs on bacterial growth: (**a**) MSSA growth curves; (**b**) MRSA growth curves; (**c**) effect of ampicillin, bAuNPs and both (0.01 mg/L Amp and 0.1 mM bAuNPs) on MSSA growth expressed in AUC as percentage of control; (**d**) effect of ampicillin, bAuNPs and both (0.1 mg/L Amp and 0.1 mM bAuNPs) on MRSA growth expressed in AUC as percentage of control. AUC—area under the curve; NC—normal condition, i.e., basal medium only; Amp—ampicillin; bAuNPs—biosynthetic gold nanoparticles; Both—a mixture of bAuNP and ampicillin; MSSA—Methicillin-susceptible _S. aureus_; MRSA—Methicillin-resistant _S. aureus_; CFU—colony-forming units. **\(p<0.01\), ***\(p<0.001\). In previous studies, the quantitative evaluation of the efficacy of antibiotic-AuNP conjugates against bacteria remained uncertain. Most reports determined the Minimum Inhibitory Concentrations (MICs) of the agents by measuring the decrease in optical density or by utilizing aggregated AuNPs [40]. However, in the present research, colony forming unit counting was employed as a quantitative method to assess the individual and combined effects of each agent on bacterial viability. This approach provides a more accurate and reliable measure of the impact on bacterial growth and survival. The observed synergistic effect of ampicillin in combination with bAuNPs suggests that bAuNPs play a role in enhancing the penetration of ampicillin into the bacterial cell wall. This enhanced penetration leads to increased interactions between ampicillin and bacteria, ultimately improving the efficacy of the antibiotic. It is important to note that the resistance of _S. aureus_ to antibiotics, such as ampicillin, is primarily attributed to the production of the penicillin-binding protein 2a (PBP-2a). This protein exhibits lower affinity for \(\beta\)-lactam antibiotics, thereby reducing the effectiveness of these drugs [41]. Consequently, the results obtained in this study imply that bAuNPs might enhance the affinity of bacteria to ampicillin, potentially overcoming the resistance mechanism mediated by PBP-2a. This enhanced affinity could disrupt the bacterial cell wall, further contributing to the reduction in bacterial growth and viability. Nevertheless, the exact mechanism of action of bAuNPs on bacteria remains incompletely understood and necessitates further investigation. Future research efforts can focus on elucidating the precise molecular interactions between bAuNPs and bacteria, as well as the impact of these interactions on the integrity of the bacterial cell wall. Such studies will contribute to a more comprehensive understanding of the potential applications of bAuNPs in combating antibiotic-resistant bacteria.