Factors Which Affect the Effectiveness of a Disinfectant

Disinfectants play an important role in our daily lives because of the better understanding of disease control and prevention. This applies to homes and public places, particularly hospitals. The many types of disinfectants and microorganisms they are designed to kill can, however, be affected by external factors. This can affect the result of the disinfecting process.

Concentration and Potency of Disinfectants

• In most cases, the efficacy of a disinfectant is improved if its concentration in increased. A stronger concentration should also reduce the amount of time needed to kill the microorganisms, assuming that all other variables remain constant. Iodophors, preparations containing iodine and a solubilizing agent that release free iodine when it is in a solution, are the only disinfectants to which this theory does not apply.

Temperature

• Most disinfectants increase their activity when temperature is increased. This method of increasing the effectiveness of disinfectants should, however, be approached carefully. Some disinfectants do not increase activity in raised temperatures and an increase in temperature can also all lead to the disinfectant degrading, reducing its effect.

pH Levels

• Increased pH levels can lead to two outcomes. The disinfectant molecule or the cell surface may be altered by increased pH levels. In some disinfectants, such as quaternary ammonium compounds and glutaraldehyde, increased pH improves the disinfectant's ability to kill microorganisms. In other disinfectants, including hypochlorites, phenols and iodine, the effect of the disinfectant is reduced by an increase in pH.

Water Hardness

• The high levels of minerals present in hard water, such as calcium and magnesium, can reduce the effectiveness of a disinfectant. This happens because insoluble precipitates are produced when the disinfectant interacts with the hard water minerals.

Duration of Exposure

• The type of disinfectant and the type of germ that it intends to kill can influence the minimum length of time required for a microorganism to be killed by a disinfectant. As a general rule, the longer a disinfectant is in contact with a contaminant, the greater the chance the microorganism will be killed.

Resistance of Microorganisms

• The microorganisms disinfectants are designed to kill vary greatly in levels of intrinsic resistance. One factor that provides contaminants with a level of resistance is the nature of its structure. For example, spores have a coat and cortex that act as a barrier to disinfectants. Mycobacteria can also prevent disinfectant entry as they have a waxy cell wall. More resistant microorganisms require stronger concentrations of disinfectant and a longer period of exposure to it.

Biofilms

• The production of biofilms -- thick masses of cells and extracellular materials -- may also protect microorganisms from the effects of disinfectants. These microbial communities are difficult to remove from the surfaces to which they tightly attach themselves. The microbes within these masses can be resistant to disinfectants in many ways, including production of neutralizing enzymes, genotypic bacterial variation and altering physiological features such as pH. Bacteria may be up to 1,000 times more resistant to disinfectant when it is in a biofilm than it would be in suspension.