Disinfectant Overview


Disinfection was first introduced by Lister who introduced "carbolic acid" (phenol), the first disinfectant. Today disinfectants are widely used in the health care, food and pharmaceutical sectors to prevent unwanted microorganisms from causing disease.

Disinfectant chemicals act to disrupt significant cellular structures or processes in order to kill or eliminate microorganisms. A number of different chemicals have been commercialized as disinfectants, as shown in Table 1.

Table 1. Classes of Disinfectant Chemicals

Chemical Class



Chlorine Compounds

sodium hypochlorite
chlorine dioxide
acidic chlorine sources


Virkon S, AVS Virucidal Extra

Iodine and Iodophors

tincture of iodine
povidone iodine





Fumalyse II


synthetic phenols

Multi-Phenolic Disinfectant

Quaternary Ammonium Compounds



Oxidizing Agents

hydrogen peroxide
peracetic acid





1. No current approval for general disinfection in Canada.

Sterilization & Disinfection

Sterilization is defined as the elimination of all microbial life.
Disinfection is defined as a process that eliminates many if not all pathogenic organisms. Most agricultural, veterinary and food users are aiming for disinfection since their facilities are not designed for sterilization.

Disinfectant Strength

Generally, a commercially available disinfectant will exhibit the ability to reduce microbial contamination by several orders of magnitude in a standard test method in order to be approved for use. In use however, mot all disinfectants exhibit the activity that one would expect based on standardized tests. There are many reasons for this but one of the main points to consider is the carefully controlled conditions of the standard test methods are simply mot the Same as the real world. One well known is the failure of quaternary ammonium compounds in the presence of anionic detergents and, in the case of some formulations, hard water. These conditions disrupt the binding of the quaternary ammonium compounds to the microbial cell membrane.
The other factor is that some of the targeted organisms are more difficult to kill than the standard test specimens. Figure 1 Shows the generally accepted scheme for susceptibility of microorganisms to disinfection or sterilization.

Figure 1. Microbes from least to most susceptible to disinfection.


(BSE, scrapie)


(Emeria, Cryptosporidia)


(Anthrax, Clostridium difficile)


(M. tuberculosis, M. avium)





Gram-negative bacteria (non-sporulating)



(Candida, Aspergillus)

Large non-enveloped viruses

(Enteroviruses, Adenoviruses)

Gram-positive bacteria

(S. Aureus, Enterococci)

Lipid enveloped viruses


Resistance to Disinfectant Chemicals

With the growth in concern over antibiotic resistance there have been a number of studies attempting to demonstrate a similar resistance to disinfectants in multi-drug resistant bacteria. Studies have shown that in some cases adaptations can occur that provide resistance to low levels of disinfectants however, the levels of disinfectant that these bacteria can "resist" are many times lower than the recommended use levels. Antibiotic resistant bacteria have shown similar levels of reduction in side by Side standard tests as nonresistant bacteria when disinfectants were used at the manufacturer's recommended dilutions. Generally, the resistance of microorganisms to disinfection is due to the existing cellular structures and life cycle adaptations. It is important to read the label carefully and follow the manufacturer's directions to achieve the best results.

Disinfectant Rotations

Disinfectant rotations are an idea that originated in the Health Care and Pharmaceutical Sectors to deal with the wide variety of microbial challenges that must be prevented from gaining a foot hold in very clean environments. The theory behind disinfectant rotation is that no one disinfectant will be effective against all microbes So rotating between a series of powerful disinfectants will prevent any particular microbe from establishing itself in the facility. They may be of Some benefit in facilities that disinfect on a regular basis but there is no publicly available data to support any particular scheme.

Successful Disinfection

The first step in successful disinfection is to choose a disinfectant that will act on the types of microorganism that is to be eliminated. For example, a quaternary ammonium formulation will not be effective against bacterial spores while a formaldehyde based product would. The next step is to confirm that the disinfectant is compatible with the planned application: it is difficult to disinfect bare wood Structures such as bank barns.
Disinfectants depend on binding or reaction with bacterial cell membranes to kill microorganisms. Disinfectant chemicals are not selective, formaldehyde will react with any acceptor not just microbial proteins, similar observations have been made for all the other disinfectant chemicals. It is therefore crucial to thoroughly clean and rinse all surfaces and equipment prior to disinfection. Cleaning also removes large numbers of microorganisms from surfaces or equipment so that the disinfectant will achieve large reductions in the remaining organisms due to its higher effective concentration.
Following cleaning, the disinfectant should be applied according to the label instructions. It is important not to mix insecticides or other chemicals with the disinfectant, not only might the efficacy of both the disinfectant and the insecticide be reduced, but in Some cases dangerous chemical reactions will occur. The full contact time specified on the label should be allowed prior to rinsing any surfaces or equipment that may contact feed or drinking water.
It is important to take temperature into account when determining contact times: chemical binding and reactions are strongly affected by temperature. When disinfecting in the winter, the contact times should be extended in low temperature environments and probably not attempted at all if the temperature is below freezing.

Environmental Fate

Recently, there concern has been a great deal of concern regarding the effects of "persistent organic chemicals" in the environment. The chemicals in Bio Agri Mix disinfectants are not persistent in the environment.
The phenols used in Multi-Phenolic Disinfectant are known to degrade rapidly in sewage treatment systems, water courses or air and have low mobilities in soil. Bioaccumulation of these phenols in marine organisms is mot considered a significant environmental fate of these compounds.
Formaldehyde, the active substance in Fumalyse II, is a toxic chemical due to its reactivity. In the environment, this reactivity leads to the slow oxidation of formaldehyde to formic acid. When used as directed, the formaldehyde in Fumalyse II acts in a vapour film on the surface. The formaldehyde breaks down over time due to diffusion of oxygen into the film.