Nanostructures as Antimicrobial Therapeutics

Developing countries encounter huge economic losses due to frequent epidemics of infectious diseases. The major contributing factor is the indiscriminate use of antibiotics leading to the emergence of resistant strains that are unaffected by existing antibiotics. Moreover, infectious diseases associated with the formation of biofilms composed of a large number of bacterial communities are not easily penetrable by antibiotics at normal doses. Possible routes to the generation of new antimicrobial agents include finding new targets for antimicrobial activity, combination compounds showing simultaneous action on more than one target, and new delivery mechanisms to improve target specificity. Nanomaterials have opened a new avenue as antimicrobial agents owing to their unique properties, such as surface chemistry (functionalizable structure), chemical stability, appropriate size, high surface area to mass ratio, high reactivity, stability, robustness, durability, biosafety, and biocompatibility. Nanoparticles can be utilized to either enhance antimicrobial activity of existing antibiotics, as physical agents that cause cell damage (photothermal activity), or for encapsulating antimicrobial agents for efficient drug delivery. Nanomaterials studied for their compatibility as alternative medicine include metal nanoparticles (gold and silver nanoparticles), metal oxide nanoparticles (oxides of magnesium, titanium, zinc, calcium, copper, aluminium, cesium), and organic nanoparticles (poly-ɛ-lysine, quaternary ammonium compounds, cationic quaternary polyelectrolytes, N-halamine compounds, polysiloxanes, benzoic acid, phenol, and parahydroxybenzoate esters). Inorganic nanoparticles are preferred over organic nanoparticles owing to their stability in harsh process conditions. The modes of action of these nanoparticles are variable, depending on the types of nanoparticles conjugated. These actions include damage to cell membrane by altering permeability due to generation of reactive oxygen species, release of ions that react with cell constituents, such as DNA, and sulfur-containing proteins that inhibit DNA replication and enzyme functions, respectively, contact killing by cationic surfaces or photothermal damage. Although all these nanoparticles have tremendous applications as antimicrobial agents, extensive toxicity testing is required prior to their usage in order to ascertain their effects in a biological system. This chapter will highlight the recent advancements in applications of these antimicrobial nanoparticles, their unique properties, and modes of action along with their biocompatibility issues.