  Citation: Rabiee, N.; Ahmadi, S.; Akhavan, O.; Luque, R. Silver and Gold Nanoparticles for Antimicrobial Purposes against Multi-Drug Resistance Bacteria. Materials 2022, 15, 1799. https://doi.org/10.3390/ ma15051799 Academic Editor: Cristina Della Pina Received: 13 December 2021 Accepted: 25 January 2022 Published: 27 February 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). materials Review Silver and Gold Nanoparticles for Antimicrobial Purposes against Multi-Drug Resistance Bacteria Navid Rabiee 1,2, * ,† , Sepideh Ahmadi 3,4,† , Omid Akhavan 1 and Rafael Luque 5, * 1 Department of Physics, Sharif University of Technology, Tehran 11155-9161, Iran; oakhavan@sharif.edu 2 School of Engineering, Macquarie University, Sydney, NSW 2109, Australia 3 Student Research Committee, Department of Medical Biotechnology, School of Advanced Technologies in Medicine, Shahid Beheshti University of Medical Sciences, Tehran 19857-17443, Iran; speahmadi@yahoo.com 4 Cellular and Molecular Biology Research Center, Shahid Beheshti University of Medical Sciences, Tehran 19857-17443, Iran 5 Departamento de Química Orgánica, Campus de Rabanales, Universidad de Córdoba, Edificio Marie Curie (C-3), Ctra Nnal IV-A, Km 396, E14014 Cordoba, Spain * Correspondence: navid.rabiee@mq.edu.au or nrabiee94@gmail.com (N.R.); rafael.luque@uco.es (R.L.) † These authors contributed equally to this work. Abstract: Several pieces of research have been done on transition metal nanoparticles and their nanocomplexes as research on their physical and chemical properties and their relationship to biological features are of great importance. Among all their biological properties, the antibacterial and antimicrobial are especially important due to their high use for human needs. In this article, we will discuss the different synthesis and modification methods of silver (Ag) and gold (Au) nanoparticles and their physicochemical properties. We will also review some state-of-art studies and find the best relationship between the nanoparticles’ physicochemical properties and potential antimicrobial activity. The possible antimicrobial mechanism of these types of nanoparticles will be discussed in-depth as well. Keywords: silver nanoparticles; gold nanoparticles; antimicrobial resistance; green chemistry 1. Introduction Bacterial resistance is becoming a global challenge as microbes are continually chang- ing. Every year, 33,000 people in Europe die from bacterial resistance, so new ways to fight bacteria are required [1,2]. The increase in nosocomial and acquired infections can be a sig- nificant problem due to multi-drug-resistant bacterial pathogens (MDRs) for which current antibiotic treatments are not effective [3,4]. Antibiotics are important in fighting bacterial infections, however, in recent years they have become increasingly resistant to treating infections. Excessive application of antibiotics causes microorganisms to undergo genetic changes over time to live antimicrobial use leading to antimicrobial resistance (AMR) [5]. Excessive usage of antibiotics and the progress of antibiotic resistance has become a global concern. The increase in nosocomial infections and viral infections, including influenza as well as SARS-CoV-2 in 2019, requires rapid risk assessment and immediate prevention and treatment. Recent research has warned of a link between SARS-CoV-2 and AMR [6–10]. AMR describes the resistance of any microbe to the drugs that are applied to kill them. Drug-resistant diseases cause about 0.7 million deaths a year, and if no attempt is made to control it, AMR deaths, at worst, could reach 10 million a year by 2050 [11–13]. As a result, it can be said that AMR is one of the most important threats to human health and causes an increase in mortality. AMR is a multipart apparatus whose etiology can be influenced by the individual, the bacterial strains, and the resistance mechanisms that are established. The mechanism of AMR includes the restrictive uptake of a drug, inactivating a drug, altering a drug target, and active drug efflux [14,15]. Additionally, AMR has been reported Materials 2022, 15, 1799. https://doi.org/10.3390/ma15051799 https://www.mdpi.com/journal/materials