metallic ions so formed are intercalated between the DNA base pairs of the bacterial

genome, thus resulting in a mutation and ultimately bacterial cell death (Hemeg

2017). In this context, studies were conducted where the antibacterial effect of

metallic nanoparticles, viz., AgNPs and CuNPs, were assessed (Chatterjee et al.

2014; Dakal et al. 2016; Durán et al. 2016; Yoon et al. 2007). The study clearly

depicted that AgNPs were capable of inhibiting the cell division and DNA replica-

tion, whereas CuNPs on coming in contact with the bacterial cell resulted in the

degradation of bacterial DNA (Hemeg 2017). In a different experiment, a combina-

torial approach employing both X-ray irradiations and BiNPs was used as potent

vectors for antibacterial activity. The study pointed toward an efficient killing of the

pathogen bacterial population. The exact mechanism behind this vicious killing was

found to be the generation of free radicals, which brought intricate damage to the

nucleic acid component (viz., DNA) of the bacterial genome (Hemeg 2017;

Lellouche et al. 2012a).

11.3.6 Adsorption of Nanoparticles in Bacterial Cells (NP Interaction

With Cell Barrier)

The level of toxicity of NPs is greatly governed by the electrostatic or charged

interactions occurring between the NPs and the bacterial cell surface. It has been

noted that a positively charged particle tends to establish much-enhanced cytotoxic-

ity as compared to its negatively charged counterparts (Hemeg 2017). Keeping this

point in consideration, surface-engineered TIO2 NPs (AgNP-impregnated N-doped

titania) were prepared by Wong et al. (2015). It was deciphered that the prepared

NPs were able to establish an effective bridging, and they were readily absorbed into

the bacterial cell surface. The study also pointed out that this swift translocation of

NPs on the cellular surface resulted in enhanced cytotoxicity. The major mechanism

behind this toxicity generation in the bacterial cell was found to be the initiation of

redox reactions, which further lead to an escalation in the oxidative stress levels.

Damage to bilayer lipidic membrane and intracellular proteins were some other

detrimental effects, which originated due to the adhesion of these metallic particles

(Hemeg 2017; Wong et al. 2015).

11.3.7 Altered Bacterial Membrane Permeability

In a series of studies, researchers prepared polyvinyl alcohol (PVA)-stabilized

AgNPs (Dakal et al. 2016; Durán et al. 2016; Hemeg 2017; Sirelkhatim et al.

2015). The outcomes of the study clearly demarcated that the metallic ions thus

formed adhere to the charged lipopolysaccharide membrane. This results in altered

cellular membrane permeability and a subsequently enhanced ROS level production.

Further, it was noticed that these factors lead to an alteration in the viscosity of the

cellular membranes, thereby inhibiting and disrupting the respiratory transport

mechanisms (electron transport chain, ETC) as well as electrochemical proton

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A. Parmar and S. Sharma