Enteric bacterial human pathogens, i.e., Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Klebsiella pneumoniae, are the major cause of diarrheal infections in children and adults. Their structure badly affects the human immune system. It is important to explore new antibacterial agents instead of antibiotics for treatment. This project is an attempt to explain how gold nanoparticles affect these bacteria. We investigated the important role of the mean particle size, and the inhibition of a bacterium is dose-dependent. Ultra Violet (UV)-visible spectroscopy revealed the size of chemically synthesized gold nanoparticle as 6–40 nm. Atomic force microscopy (AFM) analysis confirmed the size and X-ray diffractometry (XRD) analysis determined the polycrystalline nature of gold nanoparticles. The present findings explained how gold nanoparticles lyse Gram-negative and Gram-positive bacteria.

Metallic nanoparticles (NPs) for medical applications have been documented since earlier times. Advancement in modern medicines results in an increase in utilization of NPs for medical purposes due to their antibacterial, antiviral, antifungal, anti-inflammatory, and antiangiogenic properties. In this chapter, three metallic NPs are studied extensively as powerful nanoweapons for the destruction of bacteria. Recent research gives evidence that metallic NPs are very effective in supporting antimicrobial activities. The chemically and laser-ablated silver, gold, and copper NPs exhibited enhanced antibacterial activity than previously reported. The antibacterial mechanism was found dose- and size-dependent and was more profound for Gram-negative bacterium as compared to Gram-positive ones. The dose calculations of minimum inhibitory concentration (MIC) with NPs have been calculated for both Gram-positive and Gram-negative bacteria. The maximum zone of inhibition by disk diffusion was also experimented against various bacteria. These NPs exhibit excellent performance physically, catalytically, and chemically. Present study will be beneficial in areas of environment, information technology, health, cosmetics, and food department. This chapter will cover the details of fabrication and antibacterial activity results of silver, gold, and copper NPs. This chapter endeavors to demonstrate the use of metallic NPs as an alternative antibacterial nanobiotics.