The Silver Nanoparticle (Nano-Ag): a New Model for Antifungal Agents

In recent years, a rapid increase in microbes that are resistant to conventional antibiotics has been observed (Goffeau, 2008). Especially, the frequency of infections provoked by opportunistic fungal strains has increased dramatically. Even though the majority of invasive fungal infections are still due to the Aspergillus or Candida species, the spectrum of fungal pathogens has changed and diversified (Denning, 1991; Ellis et al., 2000; Odds et al., 2003). Azoles that inhibit sterol formation and polyenes that bind to mature membrane sterols have been the mainstays regarding antifungal therapy for several decades (Kullberg & de Pauw, 1999; Sheehan et al., 1999). However, not only the emergence of fluconazole resistance among different pathogenic strains but also the high toxicity of amphotericin B (Alexander & Perfect, 1997; Mukherjee et al., 2003) has prompted research on new antifungal agents (Kontoyiannis et al., 2003). Bio-nanotechnology has emerged as an integration between biotechnology and nanotechnology for developing biosynthesis and environmental-friendly technology for synthesis of nanomaterials. We specifically regarded nanoparticles as clusters of atoms in the size of 1-100 nm. ‘Nano’ is a Greek word synonymous to dwarf meaning extremely small. The use of nanoparticles is gaining impetus in the present century as they posses defined chemical, optical and mechanical properties. Among them, the metallic nanoparticles are most promising as they contain remarkable antibacterial properties due to their large surface area to volume ratio, which is of interest to researchers due to the growing microbial resistance against metal ions, antibiotics, and the development of resistant strains (Rai et al., 2009; Gong et al., 2007). Different types of nanomaterials like copper, zinc, titanium (Schabes-Retchkiman et al., 2006), magnesium, gold (Gu et al., 2003), alginate (Ahmad et al., 2005) and silver have been developed but silver nanoparticles (Nano-Ag) have proved to be most effective as they exhibit potent antimicrobial efficacy against bacteria, viruses and eukaryotic micro-organisms. However, Nano-Ag used as a disinfectant drug also has some risks as the exposure to silver can cause argyrosis or argyria; it can be toxic to mammalian cells (Gong et al., 2007). 15