# Review on Silver Nanoparticles as a Novel Class of Antibacterial Solutions
## 4 Silver Nanoparticles and Their Antibacterial Role  
For the last 30 years, the pharmaceutical industries have focused on developing new antibiotics that have the ability to better fight against DNA replication, protein synthesis and bacterial cell wall synthesis. Despite this progress, a high fatality rate is still present due to the rise of antimicrobial resistance in bacterial infections. Bacterial resistance to the traditional antibiotics is a great healthcare issue with huge impact worldwide [42].  
There is an increasing growth on using nano materials and they are becoming an important part of our lives. Efforts are made towards discovering non-toxic and cost-effective materials that can be used for various applications in industry, medical, pharmaceutical and cosmetic domains. An important application of such materials is drug-resistant bacteria and diseases control [43]. Nanoparticles obtained from silver, gold, platinum and semiconductors can be used with success as delivery agents for carrying small molecules such as drugs. Nanoparticles became highly effective against bacteria due to their antimicrobial activity because of their large surface area allowing high synergy arising from multivalent interactions [44].  
Among the variety of engineered nanoparticles that have been used in antibacterial treatments, silver (Ag) nanoparticles is the most widely used antibacterial nano agent because of its broad-spectrum antimicrobial properties and strong antimicrobial effectiveness against multiple bacteria, viruses, and fungi [45]. The first evidence of using silver in medicine dates back to 1881, when it was used to prevent eye infections in neonates, and later on, in 1901 as internal antisepsis. Nowadays, drugs containing silver such as silver nitrate and silver sulfadiazine are commonly used to treat dermal burns, wounds and to remove warts [1].  
Scientists agree that Ag nanoparticles interact with the bacterial cell envelope, however it is still unknown what the primary cellular target is [46]. Silver nanoparticles are antibacterial agents, capable of fighting against 650 types of diseases. Recently, many publications discovered proof for the antibacterial activity of Ag nanoparticles combined with common antibiotics, especially against multidrug resistant bacteria including _Staphylococcus aureus_ and _Escherichia coli_[6; 42; 47; 48].  
An increased antibacterial activity can be observed when combining Ag nanoparticles and antibiotics, especially against drug-resistant bacteria [6]. In recent times, this combination has been considered a potential method to overcome bacterial drug resistance. Binding to various antibacterial agents for obtaining a higher antimicrobial activity was proposed. Several studies have been studying Vancomycin capped with Ag nanoparticles. While some autors reveal improved effects against both Gram -positive (_S. aureus_) and Gram- negative (_E. coli_) [44]. Recent studies show that the nanomaterial is capable of developing a better antibacterial activity against Gram positive bacteria but not against Gram negative bacteria.  
During the First World War, silver was the most used substance in fighting and treating soldiers' infections [2].  
Silver nanoparticles have proven a high antimicrobial activity and a low cytotoxicity levels when compared to particles obtained from other heavy metals like gold, platinum and zinc. They can bind to cells and restrict enzyme activity, destabilize the cell membrane and eventually lead to cell death [45].  
Studies have demonstrated that AgNP could induce: cyto-toxicity, geno-toxicity, inflammatory response, DNA damage, ultimately cell death. Cell's membrane and neuronal structures prolonged contact may lead to: skin diseases, argyria disease (blue skin) [45].