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The Antimicrobial Activity Of Selected Silver Products

by Dr Robert Rowen MD and Dr Dennis Harper DC ND(more info)

listed in infections and inflammation, originally published in issue 225 - October 2015

Antimicrobial Silver Graphic

The antimicrobial activity of a group of silver-based products was assessed by comparing their ability to kill MRSA (Methicillin-Resistant Staphylococcus aureus). Silver has been used for decades for its known antimicrobial effects.[1-4] Since many silver-based products have made claims of superiority over other brands, two eminent oxidation therapy specialists Dennis Harper DC ND  and  Robert Rowen MD recognized the value of conducting an independent and unbiased study that would definitively assess the antimicrobial efficacy of several well-recognized silver products. To this end, they contacted Dr Richard Robison, a microbiologist with many years of experience in disinfection and infection control.  The product identities were not disclosed prior to testing.     


The core purpose of every silver-based health product is to kill pathogenic microorganisms. In this initial study conducted at a major university laboratory, the kill rates of five silver-based products on a common and feared microorganism, MRSA; a deadly pathogen responsible for killing thousands of people each year worldwide, were determined.


Dr Rowen and Dr Harper acquired five silver-based products by purchase through normal retail channels. Harper’s acquisitions were shipped to Dr Rowen, who then blinded all five original bottles and randomly labelled each with letters A-E. Dr Rowen alone kept key codes for identifying the products.  He sent the blinded products directly to the microbiology lab, marked simply with a letter A to E.  Neither Dr Harper nor Dr Rowen was informed of the antimicrobial testing results. The test results were sent directly from the microbiology lab to George Gaboury, President of the San Francisco Tesla Institute, a grass roots organization which promotes the advancement and greater public awareness of science.  After receiving the test results, Gaboury was independently sent the key codes by Dr Rowen. Gaboury then matched the lab results to the specific products A-E, in public at a scheduled meeting of the Tesla society.  The actual lab test results were reported to the group by Gaboury in an unaltered format.

Each product was evaluated on the same day, by the same technician, using the same test organism suspension. A suspension test was used, similar to that described by March, et al.[5] Briefly, the test suspension was prepared by growing a 5 ml culture of Methicillin-resistant

Staphylococcus aureus (MRSA) organisms, ATCC 43300, in Nutrient Broth at 37 °C for 24 hr. The 5 ml culture was pelleted by centrifugation, washed with five ml sterile 18 MΩ [Megaohm] purified water, centrifuged again, and re-suspended in a final volume of one ml sterile purified water. This produced a suspension containing about 2.97 billion organisms/ml. A 9.9 ml aliquot of each test product was added to a 50 ml polypropylene sterile centrifuge tube. Tubes were equilibrated in a 20°C water bath. Then, 0.1 ml of the MRSA test suspension was added to each tube at time zero. After a two-minute contact time, 1 ml of this disinfectant/MRSA mixture was added to 9 ml of neutralizer solution.  The tube was mixed thoroughly and allowed to sit for two minutes. The neutralized suspension was then serially diluted in 9 ml blanks of physiological saline solution (PSS). The number of viable organisms in selected dilution tubes was assayed by membrane filtration. One ml aliquots were plated in triplicate. The membranes were washed with about 100 ml of sterile PSS and removed to Columbia Agar plates. The plates were incubated at 37 °C for 24 and 48 hours. The number of colonies on each filter was counted, and log reduction and percent kill values for each product were computed. Titres of the MRSA test suspension were computed and appropriate neutralizer and sterility controls were performed.


There was a highly significant difference between the five formulations, in their ability to kill MRSA in 2 minutes. Log reduction [(-Log(S/S0); where S = concentration of viable  organisms after the specified contact time; and S0= the initial concentration of viable organisms at time zero] and percent kill [(1-(S/S0)) ×100] values can be seen in Table 1. One silver product, Advanced Cellular Silver (ACS) 200 Extra Strength was found to be approximately 4,000 times more effective in antimicrobial activity than the second most effective silver-based product, Ph Stuctured Silver, and approximately 1,000,000 times more powerful in antimicrobial activity than Argentyn 23®, OXYSILVER® and American Biotech Labs ASAP® Silver. The complete study, including testing methods and results, can be requested by email.

Table 1

Table 1


Dennis Harper DC ND and Founder of O3 Medical Services, specialist in ozone and vitamin treatment, stated: “ACS 200 Extra Strength could change the landscape in significantly strengthening antibiotics for fighting infections quickly and effectively. I was challenged by my fellow peers to find the best silver product, and up until now, no one had independently tested the comparative bacterial kill rates on a range of silver-based solutions. These results could pave the way for more effective patient treatment.”

Dr Rowen and Dr Harper have taught at ACAM’s oxidation workshop, where many questions arose regarding conflicting data from various silver companies. These questions led to performing this independent study. Dr Rowen says, “Until now it was a difficult process sorting out information attached to various silver products.  We (Harper and Rowen) consulted with Dr Richard Robison (Professor of Microbiology) about designing a valid test. He advised “You are attempting to kill microorganisms with silver, so keep it simple with a standard kill test performed in an identical manner on the various products, a test which will demonstrate if the products actually do what you desire them to do.”” 

The kill rate effectiveness was assessed with a contact time of 2 minutes and the results are expressed as both log reductions and percent kill.  For accuracy, plating on each dilution was performed in triplicate.  For the layman, who might not understand the significance of logarithmic reduction, consider the Richter scale of earthquake magnitude, which is expressed in a log format. A 7.0 earthquake is 10 times more powerful than a 6.0.  A 6.0 earthquake is 1000 times more powerful than a 3.0.  As revealed in this study, ACS 200 Extra Strength had a log reduction of 6.35, compared with that of the second best product at 2.74. ACS 200 Extra Strength had greater than 3.61 log kill over the closest competitor, representing a 4,000 times greater kill than Solution A. ACS 200 Extra Strength had a percent kill rate of 99.999955%, which was close to complete kill of the test suspension (over 20 million MRSA organisms) within 2 minutes. 

How does this research affect you and me?  Dr Harper added, “We cannot make broad-stroke conclusions about any particular product based on the results of a single study, and believe it would be inappropriate to do so. In partnership, we will continue to fund further independent studies to reinforce the consistency of these truly amazing results. At the present, we have identified a highly effective silver-based solution which, when administered with antibiotics, should provide far superior patient outcomes. These test results are readily available to anyone who wants to contact me and find out more.”

Dr Rowen commented, “One must appreciate the log scale. Let’s start with 2,970,000,000 (2.97 billion) organisms. The initial dilution caused by mixing the organism with the disinfectant, gives us 29.7 million organisms/ml at time zero. Exposure to the second best product caused a 2.74 log reduction (a 99.82% kill) in viable organisms, leaving over 10,000 living MRSA organisms.

ACS 200 Extra Strength caused a 6.35 log reduction (99.999955% kill) and left less than 3 viable organisms. The other three products left over 2.5 million living MRSA organisms, in the given time period of exposure. This is simply too huge a difference to ignore, and begs that follow-up studies be conducted. This may be a huge breakthrough in the management of infection, especially in the light that silver is synergistic with oxidation therapy” 


  1. Ip, M., Lui, S.L., Poom, V.K.M., Lung, I., Burd, A. Antimicrobial activities of silver dressings: an in vitro comparison. J Med Microbiol, 55:59-63. 2006.
  2. Kim, J., Kwon, S., Ostler, E. Antimicrobial effect of silver-impregnated cellulose: potential for antimicrobial therapy. J. Biol. Engineer., 3:20-28. 2009.
  3. Li, Y., Leung, P., Yao, L., Song, Q.W., Newton, E. Antimicrobial effect of surgical masks coated with nanoparticles. J Hosp Infect, 62:58-63. 2006.
  4. Rupp, M.E., Fitzgerald, T., Marion, N., Helget, V., Puumala, S., Anderson, J.R., et al. Effect of silver-coated urinary catheters: efficacy, cost-effectiveness, and antimicrobial resistance. Am J Infect Control, 32:445-450. 2004.
  5. March, J. K., Cohen, M. N., Lindsey, J. M., Millar, D. A., Lowe, C-W, Bunnell, A. J., O’Neill, K. L., Schaalje, G. B., Robison, R. A. 2012. The differential susceptibility of spores from virulent and attenuated Bacillus anthracis strains to aldehyde- and hypochlorite-based disinfectants. MicrobiologyOpen, 1-8, doi: 10.1002/mbo3.45.


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About Dr Robert Rowen MD and Dr Dennis Harper DC ND

Dr Robert Rowen MD  has been intensely involved as a clinician in oxidation therapy since 1986. He currently serves as ACAM’s oxidation workshop chairman and teaches oxidation therapy seminars. He practises in Santa Rosa California and may be contacted via

Dr Dennis Harper DC ND has been practising ozone therapy for many years and practises in Orofino, Idaho.   He recently joined the ACAM oxidative workshop teaching staff and may be contacted via

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