There is a growing increase in number of bacteria exhibiting antibiotic resistance.  Penicillin, which once was an effective antibiotic to a lot of bacteria, is now only given as a last resort for preventing infection.  Bacteria are also starting to show resistance to Amoxicillin, and also to co-trimoxazole.   Because of this, studies and research are conducted to look for an alternative form antibacterial medication.  Because of this, science is now putting focus on silver.  The antimicrobial properties of silver have been used for centuries, starting from Ancient Greece.  It is a widely accepted fact that silver ions as well as silver-based compounds are toxic to micro-organisms, showing highly efficient biocidal effects on up to 12 species of bacteria.  In the advent of nanotechnology, silver nanoparticles are being looked into as an effective way to control infection.  The silver nanoparticles antimicrobial properties are highly significant and more effective against bacteria compared to their bulky counter parts.  Because the amount of silver used in the application scientists hope to also reduce the toxic side effects normally associated with silver based treatments. 

A study by a group of scientists who are experts in certain fields was conducted on the antimicrobial properties of silver nanoparticles.  The silver nanoparticles were tested against common bacteria that are causing common infections and diseases to man.  Escherichia coli, yeast, and Staphylococcus aureus were inoculated on a Muller Hinton agar plates.  Several plates of these micro-organisms were prepared to compare the silver nanoparticles antimicrobial properties to those of Itraconazole and gentamicin.  The plates were incubated for 24 hours at a temperature of 37 ^™C. Several plates were also made to test silver nanoparticles antimicrobial properties in various concentrations to see how this would affect the efficacy of silver nanoparticles.

The yeast that was isolated from bovine mastitis that was treated in different plates of itraconazole and silver nanoparticles of 33 nM revealed the same inhibition of growth.  Significant inhibition of growth was also observed in a separate plate givne with 13.2 nM.  The study also revealed that silver nanoparticles are highly effective against Escherichia coli with a minimal inhibitory concentration of 3.3 nM and 6.6 nM.  The conclusion was, the higher the concentration of silver nanoparticles, the better inhibition on bacterial growth.  The same cannot be said for Staphylococcus aureus.  There was no significant inhibitory effect on growth even in high concentrations of compared to the effects of gentamicin.  The minimum inhibitory concentration of silver nanoparticles for Staphylococcus aureus was found to be more than 33 nM. 

The effects of silver nanoparticles antimicrobial properties were studied under scanning and transmission electron microscopy (SEM and TEM).  It was observed that the Escherichia coli exposed to the silver nanoparticles formed indentations or holes on the bacterial cell wall.  The indentations were caused by a significant accumulation of silver nanoparticles.  The morphological change on the cell wall resulted to significant increase in permeability.  Cell death was inevitable in this case. 

The silver nanoparticles antimicrobial properties were also tested against HIV-1. Glycerine was used for the PVP-coated silver nanoparticles as a dissolving agent.  These were around 6.53 in size.  In another preparation, serum albumin was used.  The elements of sulfur, oxygen, and nitrogen helped stabilize the nanoparticles which are of 6.53 nm.  The prepared silver nanoparticles were tested against HIV-1, in vitro, and in the samples were incubated at 37 ^™C.  The samples were checked 24 hours later and 0% of pathogens were reported living.  The study revealed that a concentration greater than 25 μg/mL for silver nanoparticles is effective in inhibiting HIV-1 cells.  The 10 nm size of silver nanoparticles played a major role in its effectiveness against the virus.  It is believed that the nanosilver utilized the gp120 glycoprotein knobs of the virus for bonding with the use of sulfure.  Because of this, HIV-1 is prevented from binding with the host cell, eventually causing demise of the virus because of nutrient deprivation.  Although this may mean that silvernano particles can treat HIV-1, further research and study is needed.  There is not enough information on what would result on the human body after prolonged exposure to silver nanoparticles.  As of now, scientists are still conducting experiments on creating a preventive cream for HIV-1 to be tested on humans.  With no guaranteed certainty that the cream would work efficiently against the virus, the study is very limited in terms of test subjects. 

                Use of silver nanopartices antimicrobial properties is being tested as an active ingredient in antimicrobial gels.  For this purpose, a minimum inhibitory concentration (MIC) of 0.78-6.25 μg/mL and a minimum bactericidal concentration (MBC) of 12.5 μg/mL are used against standard reference cultures along with multidrug-resistant organisms.  Basing on the study, silver nanoparticles were effective against gram negative bacteria by showing a 3 log₁₀ decrease in 5−9 hours.  In comparison, silver nanoparticles were not as effective against gram-positive bacteria, showing a 3 log₁₀ decrease in 12 hours.  It is also effective against fungal activity by showing a 50% inhibition with a concentration of 75 μg/mL against Aspergillus niger.  It also showed significant activity against Candida albicans with a minimal inhibitory concentration of 25 μg/mL.

Silver nanoparticles antimicrobial properties were also tested in the presence of antibiotics.  The investigation revealed the following results:  

Ø  Synergistic activity with:

o   Ceftazidime

Ø  Additive behavior with

o   Streptomycin

o   Kanamycin

o   Ampiclox

o   Polymyxin B

Ø  Atagonistic behavior with:

o   ChloramphenicolThe length of bacterial growth inhibition was also measured after exposure to silver nanoparticles.  It was observed that Pseudomonas aeuginosa was inhibited for 10h 30mins; 1h 30mins for Staphylococcus sp.; 1h 40mins for Candida albicans.  The findings reveal that a therapeutic regimen must be established to ensure that silver nanoparticles are sustained in the environment. 

Silver is known to be less toxic to humans, yet still possess effective antimicrobial properties.  This is highly essential for effective treatment of burns in the presence of transient bacteremia where fast and efficient treatment is needed.  The present form of silver nanoparticles present in drugs is neutralized by biological fluids.  With long-term-use of these medications, several cosmetic manifestations are noted such as argyria and delayed wound healing.  Still, the use of silver nanoparticles antimicrobial effects are highly sought after because of its broad spectrum activity, high rate of effectiveness, and low cost.  Research is being done to find superior forms of silver-based antimicrobial agents. 

 

Study Shows Silver Nanoparticles Attach to HIV-1 virus:  http://www.physorg.com/news7264.html

Antibacterial efficacy studies of silver nanoparticles against Escherichia coli ATCC-15224: http://prr.hec.gov.pk/chapters/2068-6.pdf

Silver nanoparticles as antimicrobial agent: a case study on E. coli as a model for Gram-negative bacteria: http://www.ncbi.nlm.nih.gov/pubmed/15158396