electrostatic attraction, van der Waals forces, receptor ligand, and hydrophobic

interactions (Armentano et al. 2014; Gao et al. 2014; Li et al. 2015; Luan et al.

2016; Wang et al. 2017). This direct interaction helps in lodging the NPs inside the

cellular periphery of the bacteria where they disrupt the cellular morphology (cytosol

shrinkage, cell wall rupturing, and membrane detachment) (Baranwal et al. 2018;

Dakal et al. 2016). Further, they bind with the essential biomolecules (viz., DNA,

RNA, protein, and lipids) and interfere with the underlying metabolic pathways

ultimately resulting in altered cellular function and apoptosis (Baranwal et al. 2018;

Dakal et al. 2016; Li et al. 2008; Wang et al. 2017).

The antimicrobial efficacy of nanoparticles can also be corroborated by the fact

that they are capable of de-phosphorylating the tyrosine residues present in essential

proteins hence modulating the signal transduction pathway (Baranwal et al. 2018;

Dakal et al. 2016). Another vantage point, which came into light, was the enhance-

ment in the permeability index of the bacterial cell, which resulted in an escalated

delivery of active payload cargo. This might be ascribed to the sequence of irrevers-

ible changes occurring in the morphology of the cellular compartments owing to the

interaction of NPs with a sulfur group present in cell wall proteins (Baranwal et al.

2018; Ghosh et al. 2012).

It has been deciphered that the surface charge (zeta potential) plays a key role in

deciding the antibacterial efficacy of the nanoparticulate system, as it tends to govern

the electrostatic interaction occurring between the NPs and bacterial cell (Farouk

et al. 2018). A positive charge on the corona of the NPs allows them to interact

strongly with the negatively charged cell membrane ultimately leading to disrupted

cellular organelles, bacterial flocculation, and reduced survival rate (Farouk et al.

2018). Apart from these, there are certainly other mechanisms such as cessation of

translation and transcription process, interrupted cell division, and cell lysis due to

the production of toxic ions by NPs, which are found to be responsible for the

generation of genotoxicity and cytotoxicity in bacteria (Farouk et al. 2018; Hajipour

et al. 2012). The most eminent antibacterial mechanisms are as follows (Farouk et al.

2018; Hemeg 2017; Wang et al. 2017; Table 11.1).

11.3.1 Damage to the Cellular Membrane

A nonspecific mode of action is displayed by the NPs on the cellular membranes;

however, an exact mechanism is yet to be discovered (Farouk et al. 2018). Never-

theless, it has been hypothesized that a certain class of cationic cyclic decapeptides

commonly known as polymyxin are responsible for the antibacterial activity

(Aruguete et al. 2013; Farouk et al. 2018), as they work in an orderly fashion and

are responsible for disrupting the bacterial cell membrane. Another hypothesis,

which has been formulated to substantiate the antibacterial efficacy of the NPs,

relies upon the fact that maintenance of direct contact between NPs and bacterial cell

results in an augmented cellular permeability. This further results in the formation of

“voids” or hollow spaces, thus suggesting subsequent damage to the lipidic bilayer

11

Nanoparticles: A Potential Breakthrough in Counteracting. . .

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