Antimicrobial Efficacy of Biogenic Silver and Zinc Nanocrystals/Nanoparticles to Combat the Drug Resistance in Human Pathogens

*Gulzar Ahmed Rather, Saqib Hassan, Surajit Pal, Mohd Hashim Khan, Heshu Sulaiman Rahman and Johra Khan*

## **Abstract**

The emergence of biogenic nanomaterials as novel antimicrobials introduces a new paradigm in human health care. Based on the recent reports of the World Health Organization, infectious diseases pose one of the greatest health challenges. Increased multi-drug resistance prevalence among human pathogens, due to the inefficiency of commercially available antimicrobial drugs in the market is a great threat to humans. The poor solubility, stability and side effects of the antibacterial therapy prompted the researchers to explore new innovative strategies for developing new antimicrobials. Recently, biogenic nanoparticles have proven their effectiveness against multidrug-resistant (MDR) pathogens as an alternative to conventional antibiotics. Biogenic nanoparticles such as silver nanoparticles (AgNPs) and Zinc Oxide nanoparticles (ZnONPs) are easy to produce, biocompatible, provide enhanced uptake and are eco-friendly. Moreover, the capping of the biogenic nanocrystals provides an active surface for interaction with biological components, facilitated by free active surface functional groups to enhance their efficacy and delivery. Inorganic nanocrystals (AgNPs and ZnONPs) are effective both as nano-bactericides and as nanocarriers against sensitive and MDR) pathogens. The present chapter focuses on the utilization of the recent nanosystems to combat drug resistance in human pathogens. Nanomedicine represents a new generation of potiential antimicrobial candidates capable of combating the drug resistance in various pathogenic organisms.

**Keywords:** Antimicrobials, MDR, AgNPs, ZnONPs, nanocrystals, biogenic nanoparticles

#### **1. Introduction**

Nanotechnology is regarded as a new discipline that has a significant influence on human life in several respects with various applications [1]. Current nanoscience research is based on nanoparticle synthesis. Metal nanoparticles are used for a wide range of applications including biosensors, organic marking, cancer therapy, textiles, household and industrial applications etc. Silver nanoparticles AgNPs are mostly used in wound dressings, care of the eye, oral hygiene, biomaterials of bone substitutes, antimicrobial and anti-inflammatory drugs as well as in the coating of catheter products as anti-inflammatory and antimicrobial agents [2]. Silver is a stable and non-hazardous antibiotic agent used for centuries [3]. Most antimicrobials have many disadvantages including low stability, environmental toxicity and the lack of specificity towards the target microorganisms [4]. Few other antimicrobials are extremely irritating and expensive to develop [5].

Silver has the unusual property of binding cellular components that are far larger than nuclear acids [6]. AgNPs may be synthesized employing physical, chemical and biological processes. The majority of the physical and chemical processes of synthesizing nanoparticles have many disadvantages such as low yield, strong reducing agents, energy-intensive mechanisms, uneven particle size and aggregate instability, hazardous waste production, difficulty to scale up and expensive organo-metallic precursors are required [7]. Biological approaches for the synthesis of nanoparticles are regarded as more stable and efficient [8]. For several nanoparticles like gold, silver, platinum and palladium, titanium dioxide, magnetite and cadmium sulphide, the most possible bio-factories are bacteria. Bacteriamediated AgNPs synthesis is preferred in comparison with other techniques.

Furthermore, bacteria mediated AgNPs are simpler to grow and environment friendly. Both intracellular (biomass) as well as extracellular (cell extracts) synthesis of silver nanoparticles can be performed. Intracellular approaches include the release of synthesized nanoparticles through ultrasonication and additional reactions with specific detergents. It is therefore essential that the AgNPs are synthesized with extracellular methods because of their easy downstream processing that supports large-scale development [7, 9, 10]. There is now a prevalence of multiple tolerance to antibiotics by various clinical infections and pathogens of the urinary tract, caused by excess antibiotics and by an accumulation of antibiotics in the system. This kind of resistance is exhibited by *Staphylococcus* sp., *Streptococcus* sp., *Klebsiella* sp., *Enterococcus* sp., *Proteus* sp., *Pseudomonas* sp. and *E. coli* due to their biofilm-forming potentials [11]. The use of antimicrobial silver nanoparticles will eliminate the multiple-drug resistance, which is a suitable option for antibiotics [12]. Biofilm formation has been regarded as the global barrier in avoiding catheterrelated infections in the field of medicine [13]. The conversion of nanoparticles into therapeutic agents, however, involves a detailed knowledge of the physicochemical particularities, results *in vitro* and *in vivo*, biodistribution, pharmacokinetics and pharmacodynamics, apart from the suitable methods of their synthesis [14].
