## 3 Results and Discussion
### bAuNPs and Ampicillin Effect on Bacterial Growth and Viability  
The data obtained from the preliminary screening analysis of the effect of bAuNPs on the growth of MSSA and MRSA, tested across a concentration range of 0.5 mM to 0.0001 mM, revealed a statistically significant reduction in growth when bAuNPs were applied at a concentration of 0.1 mM. The growth inhibition percentages were 59% for MSSA (Figure 4c) and 57% for MRSA (Figure 4d), respectively (\(p<0.01\)). However, no dose-dependent effect was observed with increasing concentration of bAuNPs. These findings contradict the results reported by [PERSON] et al. and [PERSON] et al. [34; 35], but they support the notion that the effect of bAuNPs is not linearly correlated with concentration. This underscores the importance of selecting an optimal concentration. Based on this, a concentration of 0.1 mM of bAuNPs was chosen for the subsequent assays. In contrast, the results obtained for the effect of ampicillin on the growth of MSSA and MRSA exhibited an increase with increasing dose. The effect of this antibiotic showed statistical significance in MSSA (Figure 4a) at concentrations of 10, 1, and 0.1 mg/L, resulting in decreases of 66% (\(p<0.0001\)), 28% (\(p<0.05\)), and 22% (\(p<0.05\)), respectively. In MRSA (Figure 4b), decrease of 17% and 14% (\(p<0.05\)) were observed at concentrations of 10 and 1 mg/L, respectively. As the effect of the antibiotic showed a consistent pattern with increasing dose, the chosen concentrations for the subsequent assays were the lowest concentrations immediately following those that demonstrated a statistically significant bacterial growth decrease. Therefore, the chosen concentration for MSSA was 0.01 mg/L (20% growth decrease) and for MRSA, it was 0.1 mg/L (12% growth decrease). Ampicillin and bAuNPs were retested against MSSA and MRSA, and the results indicate a synergistic effect when the antibiotic is combined with bAuNPs, leading to a significant decrease in bacterial growth. The application of ampicillin resulted in a growth decline of 20% for MSSA (Figure 5a,c) and 13% for MRSA (Figure 5b,d). When bAuNPs were used alone, they exhibited a growth decrease of 60% for MSSA (Figure 4a,c) and 58% for MRSA (Figure 5b,d) (\(p<0.01\)). However, when ampicillin was applied in combination with bAuNPs, a synergistic effect was observed, resulting in a remarkable bacterial growth decrease of 84% and 78% (\(p<0.001\)) for MSSA (Figure 4a,c) and MRSA (Figure 5b,d), respectively. Figure 3: ATR-FT-IR spectrum of the bAuNPs synthesized at 58 \({}^{\circ}\)C under alkaline pH (9.0) for 24 h.  
To assess the impact on cell viability, ampicillin and bAuNPs were further tested on MSSA and MRSA under the same experimental conditions, and the number of colony-forming units (CFUs) was determined. The results, presented in Table 1 and Figure 6, indicate that both agents exhibited inhibitory effects on the cell viability of both bacterial strains. Treatment with ampicillin alone resulted in a 13% reduction in viability for MSSA (Figure 6a) and a 12% reduction for MRSA (Figure 6b). Similarly, bAuNPs demonstrated their efficacy by reducing viability by 49% in MSSA (Figure 6a) and 40% in MRSA (Figure 6b) (\(p<0.01\)). Remarkably, the synergistic effect persisted when ampicillin was combined with bAuNPs, leading to a substantial reduction in cell viability of 74% (\(p<0.001\)) for MSSA (Figure 5a) and 66% (\(p<0.01\)) for MRSA (Figure 6b). Figure 4: The effect of different concentrations of ampicillin and bAuNPs on bacterial growth expressed as the percentage of control AUC (area under the curve): (**a**) Effect of ampicillin on MSSA growth; (**b**) Effect of ampicillin on MRSA growth; (**c**) Effect of bAuNPs on MSSA growth; (**d**) Effect of bAuNPs on MRSA growth; AUC—area under the curve. NC—normal condition, i.e., basal medium only. \({}^{*}p<0.05\), \({}^{**}p<0.01\), \({}^{***}p<0.0001\). Gold nanoparticles (AuNPs) have garnered significant interest as potential carriers for antibiotic drugs.