neighboring cells (Hemeg 2017; Neethirajan et al. 2014). The spread of bacterial

infection takes place when these gradually growing bacterial cells are detached

(Hemeg 2017). In lieu of this, a strategic solution has been provided by the NPs.

Lellouche et al. prepared crystalline yttrium fluoride (YF2) nanoparticles and

assessed their characteristic antibacterial and anti-biofilm property (Lellouche et al.

2012a). The study pointed to size-dependent toxicity of prepared nanosystems. It

was noted that smaller NPs exhibited more enhanced cytotoxicity in contrast to their

bigger counterparts. The outcomes of the study revealed that an infinitesimally low

concentration (mM) of NPs was able to produce a prominent cytotoxic effect in

bacteria, thus retarding the growth of bacterial biofilm (Lellouche et al. 2012a).

Several other research groups assessed the bactericidal effect of varied NPs (viz., Se,

TiO2, CdS, ZnO, Bi, and Ag) (Dakal et al. 2016; Dhanabalan and Gurunathan 2015;

Durán et al. 2016; Guisbiers et al. 2016; Hernandez-Delgadillo et al. 2012; Lee et al.

2014; Wong et al. 2015). The outcome of the study clearly corroborated the

abovementioned findings, and similar results highlighting the antibacterial targeting

propensity of NPs were reported.

11.4

Bactericidal Activity of Nanoparticles

In response to the harsh environmental milieu, cell wall and membrane are the two

most vital defensive parameters, which offer a protective niche to the bacteria. In

other words, it can be precisely said that the exact morphology of these pathogens

remains intact due to the protective coating offered by the bacterial cell wall (Wang

et al. 2017). Owing to a complex physicochemical composition of the cellular

membrane components, the intake of NPs generally takes place through diverse

adsorption pathways in both Gram-positive (+ve) and Gram-negative (
ve) bacteria,

respectively (Lesniak et al. 2013; Wang et al. 2017). In case of Gram-negative

strains, the NPs are highly derived toward the bacterium, and a strong interaction

among them is established.

This can be explained on the basis that numerous LPS units are exposed on the

outer periphery of the cell wall, which imparts a significantly high negative charge.

This in turn offers direct communication between the NPs and the host based on

charge-charge interactions (Lesniak et al. 2013; Sarwar et al. 2015). On the other

hand, the presence of teichoic acid on the outer corona of Gram-positive bacteria

aided in widely distributing the NPs in accordance with the molecular phosphate

chains across the bacterial cell wall, thereby preventing the aggregation of functional

particles (Sarwar et al. 2015; Wang et al. 2017).

It became apparent from varied scientific studies that the NPs possess enhanced

bactericidal effect in case of Gram-positive bacteria while in their counterpart’s, viz.,

Gram-negative bacteria, showed comparatively lesser bacterial cell lysis/killing

(Wang et al. 2017). The presence of LPS, phospholipids, and proteins across the

cell wall of Gram-negative bacteria results in an altered cell morphology, thus

creating a shielding barrier across the bacteria. This penetration barrier allows only

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A. Parmar and S. Sharma