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. 2020 Jul 24;11:1669. doi: 10.3389/fmicb.2020.01669

FIGURE 1.

FIGURE 1

Mechanism of antimicrobial action in bacteria: (A) General mechanisms of action of antimicrobial peptides (AMPs). AMPs act through different mechanisms (Le et al., 2017) such as 1. Alteration in membrane integrity via electrostatic interaction with negatively charged cell membranes which kill cells, 2. Inhibition of DNA synthesis by (i) cross-linking with single- or double-stranded DNA, (ii) prevention of the DNA relaxation by inactivation of DNA topoisomerase I, and (iii) blocking of DNA replication by trapping the gyrase-DNA complex; and protein synthesis by (i) inhibition of protein translation by targeting the ribosomes, (ii) interrupting the protein-folding pathway, and (iii) rapid proteolytic activity causing the degradation of some DNA replication-associated proteins, leading to secondary inhibition of DNA synthesis, 3. Inhibition of bacterial cell wall formation by alteration of the alternating amino sugars in linear form that cross-link via peptide bridges to form the peptidoglycan layer, and 4. Inhibition of metabolic pathways by alteration of nucleic acid metabolism, including nucleotide transport and metabolism, nucleobase, nucleoside, and nucleotide interconversion. (B) Mechanisms for antimicrobial action of metal nanoparticles (MNPs). MNPs act via the following (Shaikh et al., 2019). 1. MNPs disturb cell membrane permeability by interfering with metabolic pathways and inducing changes in membrane shape and function. 2. When MNPs are in solution, metal ions are released in the environment surrounding. Metal ions generate reactive oxygen species (e.g., oxygen ions and hydroxyl radicals) and induce oxidative stress in bacteria. Oxidative stress is a key contributor in altering the bacterial membrane permeability and thus can damage cell membranes. Also, metal ions may cause cell structural changes and aberrant enzyme activities, which perturb normal physiological processes. 3. Interaction with sulfur- and phosphorous-containing compounds such as DNA, which prevent DNA from unwinding and transcription.

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