An organism is dried to a rod made of glass, stainless steel,  polished porcelain or other non-reactive material.  The rod is then submerged for 10 minutes or other claim time in a container with the disinfectant that is being tested.  There is very little clearance between the side of the container and the rod that holds the organisms.  The rod can not touch the side of the container.  The rod is then raised and allowed to drain.  A Rodac plate with agar and the appropriate nutrient is placed on the rod to remove organisms for testing.  The Rodac plate is incubated for a predetermined amount of time.  If nothing grows,  the disinfectant passes the test for that organism. 

Strength:

The method of submerging is valid for medical sterilants since they’re used in the same way for much longer periods of time (usually 12 hours or more).  This is what it takes to kill a bacterial spore like Bacillus or Clostridium.  Medical equipment that will enter normally sterile areas of the body must be free of these types of anaerobic or facultative bacteria since they can grow without the presence of air and possibly result in an infection. This is the highest level of disinfection. 

Weakness: 

How many surfaces can you submerge for any kind of necessary contact time?  What are we to do with walls, ceilings, air ducts and air handling units?  These are all hard surfaces where germs live and cross contaminate.  Shouldn’t the products registered by the EPA work as the labels claim? 

Vapors from the disinfectant can not adequately evaporate during 2 phases of the test.  The surface area of the disinfectant during the submerging period is a small percentage of the volume.  Evaporation will happen much faster if you take the same amount of disinfectant and spray it on a flat surface.  This is due to the increased surface area that is making contact with the air where vapors may escape.

The second time is when the lid of the Rodac plate is closed and placed in the incubator.  This creates an artificial atmosphere in the container during the incubation period. Chlorine evaporates much faster than the water in its dilution.  Oxygen also evaporates very quickly.  These examples also shed light on why the Hart Senate Building was so hard to remediate after contamination by Bacillus anthracis (Anthrax).

This test does not take into consideration if mycotoxins (mold),  beta glucans (mold) endototoxins (gram negative bacteria) or exotoxins (bacterial spores) are present and to what extent.  These are the toxic components of germs that may cause severe reactions to people depending on different factors.

You can’t be assured that the mold tested was able to produce a mycotoxin.  This same type of mold might be encountered in the field.  It might produce a mycotoxin that inhibits the antimicrobial activity of the disinfectant and allows the mold spore to continue living.    Stachybotrys and Chaetomium are prolific mycotoxin-producers.
 

It is important that biofilms containing these organisms are removed as much as possible.  However,  nobody has $20 million to clean a building.  Removing 95% of the organisms and disinfecting the remaining 5% is a realistic goal.  It usually takes a dose to bring a response. This is why a residual effect with low toxicity becomes very important. 
 

An organism is dried to a measured surface area.  The product is spayed according to manufacturer’s directions.  The surface is left until sufficient contact time has been achieved according to directions (usually 10 minutes).  The surface is scraped and applied to the Rodac plate with agar and an appropriate nutrient.  The Rodac plate is then placed in the incubator for a predetermined amount of time.  The test is passing if no growth occurs. 

Strength: 

This test mirrors the way you would actually apply disinfectant products to most surfaces. Evaporation is allowed to happen. Spraying or atomizing the disinfectant brings another opportunity for evaporation that the AOAC Use/Dilution Method does not utilize. 

Truth in advertising is very rare these days.  Ask the manufacturer of your favorite EPA registered disinfectant is they have performed this efficacy test.

Weakness: 

Gravity is not taken into consideration. A horizontal surface can hold more disinfectant solution than vertical surfaces (walls,  desk,  hand rails on a subway) or horizontal surfaces that are upside down (ceilings, hand rails on the subways,  air ducts).  Extra work and second treatments may need to be performed when these types of surfaces are encountered. 

This test does not take into consideration if mycotoxins (mold),  beta glucans (mold) endototoxins (gram negative bacteria) or exotoxins (bacterial spores) are present and to what extent.  These are the toxic components of germs that may cause severe reactions to people depending on different factors.

You can’t be assured that the mold tested was able to produce a mycotoxin.  This same type of mold might be encountered in the field.  It might produce a mycotoxin that inhibits the antimicrobial activity of the disinfectant and allows the mold spore to continue living.  Stachybotrys and Chaetomium are prolific mycotoxin-producers.
 

It is important that biofilms containing these organisms are removed as much as possible.  However,  nobody has $20 million to clean a building.  Removing 95% of the organisms and disinfecting the remaining 5% is a realistic goal.  It usually takes a dose to bring a response. This is why a residual effect with low toxicity becomes very important.