Microbial Interactions at Nanobiotechnology Interfaces. Группа авторов
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Название: Microbial Interactions at Nanobiotechnology Interfaces
Автор: Группа авторов
Издательство: John Wiley & Sons Limited
Жанр: Отраслевые издания
isbn: 9781119617174
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Cell membrane disruption: Interaction of the NMs with the surface of the microbes causes mechanical damage to cell wall, which in turn leads to cell wall disruption followed by leakage of the cytoplasmic content and subsequent cell death (Pal, Tak, & Song, 2007).
DNA damage: NMs or metal ions from NMs diffuse through the cell wall and effectively interact with DNA and affect or modify the morphology of the DNA. This, in turn, interrupts the duplication or replication of DNA, leading to cell death (Feng et al., 2000).
Release of metal ions: Metal ions released from the NM diffuse into the cells and bind to thiol‐containing proteins including enzymes and compromise their function. In addition to that, metal ions generally function as cofactors for a number of enzymes. Hence homeostasis of metal ions is very important for the survival of the microorganism. Metal ions released from the NM diffuse in excess into bacterial cells, affecting the homeostasis leading to dysfunction of proteins and enzymes (Feng et al., 2000).
Interrupted transmembrane electron transport: Often the interaction of NM with cell wall damages the cell wall and hampers the electron transport chain leading to the disruption of cellular respiration and eventual cell death (Lemire, Harrison, & Turner, 2013).
Oxidative stress: Few of the NMs such as metals and metal oxides prominently induce production of ROS, which includes hydroxyl free radicals, superoxides, and hydrogen peroxide. The produced free radicals further oxidize cell wall components causing their disruption and act on the internal components of cells. In few cases, the oxidation continues till the entire cell is oxidized into CO2 and water. In some specific NMs such as carbon NMs, oxidative stress is induced without the involvement of ROS, which acts by electron transfer mechanism (Jacoby et al., 1998). Schematic of the antibacterial mechanism of NMs is given in the Figure 1.4 as described by Hajipour et al. (2012).
1.10 Factors Affecting the Antibacterial Activity of NMs
As discussed earlier, the activity of any NM system depends on its physicochemical properties such as size, shape, zeta potential, crystal structure, charge, and other factors. The physicochemical factors' influence on the surface area, surface energy, and atomic ligand deficiency dictates the behavior of NMs, which in turn affects the activity of NMs. Hence it is very important to study the effect of these factors on the activity of the NMs. Schematic of the factors influencing the antimicrobial activity of the NMs is given the Figure 1.5 as detailed by Daima and Bansal (2015).
1.10.1 Size
A key advantage of any NM system is its higher surface area‐to‐volume ratio in comparison to the micro and macro structures. Practically it is possible to contain a significantly high number of smaller NMs in comparison to bigger particles in the same volume. High surface area‐to‐volume ratio owing to an increased number of particles results in exposure of greater numbers of atoms, which could increase the activity. Considering the case of antibacterial system, the formation of biofilm is a key event in the development of resistant bacteria. Exposure of a greater number of atoms on the surface results in increased interaction of NM surface with bacteria, increasing the number of reactive oxygen species at a faster rate followed by inhibition or elimination of the bacteria. Supporting this fact, several recent studies have shown that the size of NMs plays a critical role in dictating the antimicrobial property of the NM.
Figure 1.5 Schematic of the factors influencing the antimicrobial activity of the NMs.
Generally, the smaller the size of NM the higher will be the surface area with a high chance of prolonged interaction with microbial system and high diffusion through the cell membrane in comparison to bigger NMs with smaller surface area (Gurunathan et al., 2014). In the case of silver NPs, the size of the NPs clearly influences the surface area exposure, release rate of silver ions, and the antimicrobial efficacy of the particles. Similarly, ZnO NPs of smaller size (12 nm) had better antimicrobial activity in comparison to larger particles of size 45 nm due to its high cell permeability (Padmavathy & Vijayaraghavan, 2008). In another study involving the TiO2 and silica NPs, the antimicrobial property and the mechanism of action of the system were influenced by the size of titanium nanotubes (Çalışkan et al., 2014). In contrast, a study involving three different sizes of Mg(OH)2, the smallest NPs had the least antibacterial effect (Pan et al., 2013). Thus, it is necessary to consider the effect of other factors also with size in determining the mechanism action of NMs.
1.10.2 Shape
Next, to size, shape is also an important factor that affects the structural behavior and antimicrobial activity of the NMs. NMs of different shapes have shown to cause varying degrees of bacterial cell damage, mechanism of action, and antibacterial property (Cha et al., 2015). Hong et al. (2016) studied the antimicrobial property of sphere‐, wire‐, and cube‐shaped silver NPs of the same diameter. Notably, the nanoparticle with cubic shape exhibited the highest antimicrobial effect in comparison to other shapes. This was attributed to the specific facet reactivity and surface area of the cube‐shaped NPs (Hong et al., 2016). Another study was done to compare the enzyme inhibition and antimicrobial effects of the sphere‐, plate‐, and pyramid‐shaped nano‐ZnO particles. It was reported that the particles of pyramid shape showed a better β‐galactosidase enzyme inhibition and greater antimicrobial property. The system was a reversible inhibition system and worked by obstructing the enzyme similar to natural inhibitors unlike by the degradation of enzymes as reported earlier (Cha et al., 2015). In another study involving Y2O3 NPs, the particles of prismatic shape showed better antibacterial activity against Pseudomonas desmolyticum and S. aureus. The antimicrobial activity was due to the direct interaction of prismatic‐shaped particles with cell membrane followed by the membrane damage and bacterial kill (Prasannakumar et al., 2015).
1.10.3 Zeta Potential
In addition to size and shape, zeta potential (surface charge) of the NMs is also known to affect the behavior of NMs. It is clear from the literature that the surface charge of the NMs has a strong influence on the adhesion of bacteria. Since bacterial cell surface is negatively charged, NMs with positive charge exert electrostatic attraction, which helps in the adsorption of bacteria onto the surface. This is the reason behind the enhanced ROS production by positively charged NM in comparison to neutral and negatively charged NMs. However, negatively charged NMs exhibit antimicrobial property at a higher concentration through molecular crowding leading to the interaction of NM surface with bacteria.
Pan et al. (2013) studied the antibacterial activity of Mg(OH)2 prepared using different precursors (MgCl2, MgO, and MgSO4). It has been reported that positively charged Mg(OH)2 NPs prepared with MgCl2 exhibited greater antimicrobial property against E. coli in comparison to negatively charged particles prepared with MgO. This was due to electrostatic interaction between the positively charged Mg(OH)2 with the negatively charged bacterial cell membrane resulting in damage to bacterial cell (Pan et al., 2013).
1.10.4 Roughness
Although majority of the studies were done by analyzing the effect of size, shape, and surface charge of NMs on their activity, a few studies have been performed to understand the effect of roughness. In one of them, Sukhorukova СКАЧАТЬ