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Biological nano silver

Silver nanoparticles represent a prominent nanoproduct with potential application in medicine and hygiene. The inhibitory and bactericidal activities of silver ions have long been known. Some forms of silver have been demonstrated to be effective against burn infections, severe chronic osteomyelitis, urinary tract infections and central venous catheter infections. Based on these results, many silver-based antimicrobial materials have become available and several others are under development in research laboratories.
Metallic nanoparticles can be obtained by physical, chemical or biological methods. However, biological synthesis is reliable and eco-friendly, and has received particular attention. In fact, a number of different species of bacteria and fungi are able to reduce metal ions producing metallic nanoparticles with antimicrobial properties. Recently, efficient antibacterial activity was observed against multi drug resistant and highly pathogenic bacteria, including multi drug resistant Staphylococcus aureus, Salmonella typhi, Staphylococcus epidermidis and Escherichia coli by silver nanoparticles produced by the fungus F. acuminatum. Additionally, plant extracts can also be used to obtain metallic nanoparticles.
Possible Mechanisms
Silver ions react with SH groups of proteins and play an essential role in bacterial inactivation. Micro molar levels of silver ions uncouple respiratory electron transport from oxidative phosphorylation, which inhibits respiratory chain enzymes or interferes with membrane permeability to protons and phosphate. These particles can penetrate and can disrupt the membranes of bacteria.
Silver nanoparticles fight pathogenic microorganisms. It has an anti-microbial activity and toxicity. In the presence of silver ions, bacterial cells reach an active but non-culturable state and eventually die. Probably there is an impairment of DNA replication and complete disruption of the bacterial membrane after few minutes in contact with silver nanoparticles. Depending on the particle size, silver nanoparticles accumulate in cell membranes while some penetrated into the cells. A massive loss of intracellular potassium is induced by silver nanoparticles and decrease the ATP levels resulting in the loss of cell viability.
However, resistant microorganisms are also present in environments where silver salts (e.g., silver nitrate, silver sulfadiazine) are used as antiseptics, such as in burn wards of hospitals. The antibacterial activities of several antibiotics is increased when used in combination with silver nanoparticles against the Gram-negative micro-organisms.

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