**3.1 Anti-bacterial activity of AgNPs**

Silver nanoparticles (AgNPs) have emerged as a potential substitute for antibiotics in combating bacterial infections, owing to their capacity to surmount the bacterial resistance that has developed against conventional antibiotics (**Figure 3**). Consequently, the development of silver nanoparticles (AgNPs) as antibacterial agents is deemed imperative. AgNPs exhibit potential as antibacterial agents owing to their crystallographic surface structure and large surface-to-volume ratios, among other promising nanomaterials. Sondi and Salopek-Sondi's seminal study, as documented in [61], showcased the efficacy of AgNPs in combating *Escherichia coli*. The study revealed that the treatment of *E. coli* cells with AgNPs resulted in the accumulation of AgNPs in the cell wall and the formation of "pits" in the bacterial cell walls, ultimately leading to cell death. Additionally, the study demonstrated the antimicrobial properties of AgNPs. The antibacterial activity of smaller particles with a greater surface-tovolume ratio was found to be more efficient than that of larger particles in the identical *E. coli* strain [62]. Moreover, it should be noted that the antibacterial efficacy of silver nanoparticles (AgNPs) is contingent not only on their size but also on their shape [63]. Silver nanoparticles (AgNPs) were produced using four distinct saccharides, resulting in an average size of 25 nm. The AgNPs exhibited notable antimicrobial and bactericidal properties against both Gram-positive and Gram-negative bacteria, including methicillin-resistant *Staphylococcus aureus* and other highly resistant strains. As

**Figure 2.** *AgNPs have a wide range of potential applications.*

#### **Figure 3.**

*A schematic representation of the mechanisms underlying the antibacterial activity of silver nanoparticles.*

previously noted, the efficiency of AgNPs is determined not only by their size but also by their shape, as they exhibit a shape-dependent interaction with the Gram-negative organism *E. coli* [64]. Additionally, a comprehensive investigation was conducted to assess the efficacy of silver nanoparticles (AgNPs) in combating yeast, *E. coli*, and *Staphylococcus aureus* antimicrobial activity. The findings indicate that yeast and *E. coli* exhibited complete growth inhibition at low concentrations of AgNPs, whereas a minor impact was observed in *S. aureus* [65]. The present study assessed AgNPs that were biologically synthesized from the culture supernatants of *Klebsiella pneumoniae*. The impact of Ag-NPs on the efficacy of different antibiotics, including penicillin G, amoxicillin, erythromycin, clindamycin, and vancomycin, was evaluated against *Staphylococcus aureus* and *E. coli*. The results indicated that the presence of Ag-NPs led to an increase in the effectiveness of the aforementioned antibiotics [66]. In comparison to silver nanoparticles, hydrogel-silver nanocomposites exhibited remarkable antibacterial efficacy against *Escherichia coli*. The composite of chitosan-Ag-nanoparticle, synthesized in a single reaction vessel, exhibited superior antimicrobial properties compared to its constituent parts at equivalent concentrations. This can be attributed to the preferential formation of small AgNPs bound to the polymer during the onepot synthesis process, which allows for dispersion in media with a pH of 6.3 or lower [67]. The utilization of culture supernatants of *Staphylococcus aureus* for the biological synthesis of AgNPs resulted in noteworthy antimicrobial activity against methicillinresistant *S. aureus*, methicillin-resistant *Staphylococcus epidermidis*, and *Streptococcus pyogenes*. However, the antimicrobial activity against *Salmonella typhi* and *Klebsiella pneumoniae* was only moderate [68]. The present study investigated the cellular mechanisms underlying the induction of cell death by AgNPs in *E. coli*. Specifically, the study examined the leakage of reducing sugars and proteins as indicators of cell death. Moreover, it has been observed that AgNPs possess the ability to disrupt the permeability of bacterial membranes by creating numerous pits and gaps. This suggests that AgNPs have the potential to impair the structural integrity of bacterial cell membranes [69]. The AgCHX complex consisting of silver nanocrystalline and chlorhexidine,

exhibited potent antibacterial efficacy against a range of Gram-positive/negative bacterial strains and methicillin-resistant *Staphylococcus aureus* (MRSA) strains. The results indicate that the nanocrystalline Ag (III)CHX exhibited significantly lower minimal inhibitory concentrations (MICs) compared to the ligand (CHX), AgNO3, and the established benchmark. Silver sulfadiazine is a topical antimicrobial agent commonly used in the treatment of burns and other skin injuries [70].
