a certain group of entities to surpass through them and retards the movement of any

other molecule other than macromolecules.

On the other hand, a thin layer comprising of both peptidoglycan and teichoic

acid along with numerous miniscule pores is present on the cell wall of the Gram-

negative bacteria. This allows the transverse passage of any foreign material swiftly

through the bacterial cell, hence ultimately leading to disrupted cellular membranes

and apparent cell lysis/apoptosis (Sarwar et al. 2015; Wang et al. 2017). Thus, it can

be collectively said that the unique cellular composition of the vivid bacteria

provides a strategic opportunity for the NPs to invade and attack the target pathogens

in an efficient and comprehensive manner. Some of the studies depicting the

antibacterial activity of nanoparticles are summarized in Table 11.1.

Cell membrane plays a prominent role in controlling the respiratory function of

the bacteria. However, it has been depicted by ongoing studies that the respiratory

mechanism of the bacterial cell membrane is highly influenced by the activity of

nanoparticles (Erdem et al. 2015; Wang et al. 2017). Erdem et al. in their study

evaluated the cytotoxic potential of TiO2 NPs against two bacterial strains, viz.,

Gram-positive (B. subtilis) and Gram-negative (E. coli), respectively (Erdem et al.

2015). The study demonstrated an inhibited growth of bacterium due to the produc-

tion of ROS entities. On the other hand, it was also deciphered that lipid peroxidation

and disruption of the cellular respiratory pathway were induced owing to the

presence of these NPs.

In a different study, Sondi et al. investigated the bactericidal efficacy of silver

nanoparticles on Gram-negative E. coli (Sondi and Salopek-Sondi 2004). The

treated bacterial plates were further visualized under TEM to observe the bactericidal

effect of developed NPs. TEM analysis revealed the evident presence of circular pits,

which signify innate damage to the bacterial cell wall, by the NP activity. Further,

this resulted in escalated cellular membrane permeability and efflux of the NPs

inside the cellular periphery. This resulted in an inactivated respiratory electron

transport chain and lately apoptosis (Sondi and Salopek-Sondi 2004).

With recent strides in nanoparticulate therapy, another point, which came into

consideration, was the bacterial cell potential. This tends to play a pivotal role in

establishing direct communication between the NPs and bacterial cell, hence

governing the phenomenon of apoptosis (Wang et al. 2017). A perfect example

corroborating this hypothesis was demonstrated in a study conducted by Nataraj

et al. (2014). They utilized fluorescence microscopy as an invigorated tool for

assessing the detrimental bactericidal potential of TiO2-based NPs on the bacterial

cell membrane. It was observed that NP treatment resulted in an altered cell

membrane potential which became quite apparent from the marked changes taking

place in the fluoresce intensity of the cytoplasm (Nataraj et al. 2014; Wang et al.

2017).

The NPs tend to penetrate the bacterial cell wall by employing two varied

penetration mechanisms, viz.:

1. Diffusion: The first and foremost type of penetration strategy used by the NPs is

diffusion. The diffusion of nanoparticles in the bacterial cell wall or membrane is

11

Nanoparticles: A Potential Breakthrough in Counteracting. . .

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