Infection Control Today - 12/2001: Microbial Resistance and DisinfectantUse

December 1, 2001

Microbial Resistance and Disinfectant Use

By Rodney Stine

Overuse... this word rings out a warning. Too much of a good thing can be abad thing. Some types of overuse only affect our personal lives. For instance,overuse of words renders them ineffective. Overuse of objects causes them towear out. However, overuse of pesticides, antibiotics, or disinfectants is notso easily dismissed. The mode of action of each of these antimicrobials isdifferent; therefore the outcome of overuse is unique to each. These substances,and the microbes resistant to them, work in distinct ways. The concern is thatwe do not overuse these agents and create a new generation of mutated microbesso that we are limited in our ability to combat them.

Not much has been published about overuse of surface disinfectants and theirmicrobial resistance. Reports discussing these products are concerned withgeneral safety for the healthcare worker (HCW) using them. Here we look atmicrobial resistance to surface disinfectants as compared with antibiotics andpesticides.

Antibiotics and Resistance

Antibiotics work specifically against bacteria, and are one of the greatdiscoveries of the 20th century. Antibiotics, namely penicillin, becameavailable in limited use during the early 1940s. We often think of bacteria asevil, but in truth, they're not all inherently bad. Many are common residents inthe nose, throat, and intestines. The bacteria will only cause trouble if theysomehow get perturbed, or if they find a way to spread to the lungs or bloodstream. Why they do this is not yet understood.

When one of these things happens, the bacteria go into reproductive overdriveand infection starts. Antibiotics go after the bacteria and either break downthe cell walls or interfere with reproduction by blocking different biochemicalpathways. Scientists have known that bacteria could "learn" to combatthe mechanisms of antibiotics. In any colony of bacteria, there are going to bea few cells that are exceptionally strong. The vulnerable cells are attacked andnot allowed to divide, but the few strong mutant cells are left to reproduce.The result is a new generation of stronger "bugs" that are notaffected by the antibiotic. As a counter punch, we have continued to developstronger antibiotics, increased the dosage, or combine the two to overcomeinfection.

The trouble is that with each additional treatment, bacteria are givenanother chance to build up their resistance against different drugs. Antibioticsare prescribed more often than in the past and more routinely for treating upperrespiratory infections. S. Michael Marcy, MD, clinical professor of pediatricsat the University of Southern California and the University of California at LosAngeles, says, "Most upper respiratory infections are viral, andantibiotics simply have no effect on them. Their structure and reproductiveactivities are completely different." What treating a virus with anantibiotic does is create more resistance among the normal bacteria in yourbody. Thus, overuse of antibiotics can cause the resistant bacteria to outnumberthe susceptible bacteria, creating a super strain. When these normal bacteriabecome infectious, they are resistant to treatment.

Surface Disinfectants and Microbial Activity

Disinfectants, specifically surface disinfectants, work environmentally andin a totally different way than antibiotics and many pesticides. Disinfectantswork by absorbing onto any microbial cell. According to research by Stedman,Kravitz, and King, such absorption increases the permeability of the cellmembrane, ultimately leading to rupture and leakage of the contents of the cell.The cell dies. There is no chance for mutation.

What are the best disinfectants? It is well known that the long-chainquaternary compounds, which posess the greatest antimicrobial activity, arethose with at least one radical, with C8 to C18 length carbon chain. (Domagk,Deutsch Med and Wochschr 61/829) General characteristics of disinfectantsprovided by the Mississippi State Extension Service list six categories ofsurface disinfectants:

  • Alcohols. These are not recommended for surface use due to evaporation.

  • Halogens (iodines). These are broad spectrum but are corrosive. They have few reactions but are unstable at high temperatures.

  • Quaternary ammonium compounds. These have good germicidal range, are non-corrosive and non-sporocidal, are low in toxicity and are effective against vegetative bacteria, fungi, and viruses. They may, however, be deactivated by hard water.

  • Phenolics (single or multiple). These have a wide germicidal range, are very effective in the presence of organic matter, and have low toxicity. They do, however, degrade certain plastics over time and are difficult to rinse, therefore encouraging film accumulation.

  • Coal tar distillates (creason and cresylic acid). These have wide germicidal activity and are highly efficient in the presence of organic matter. They are corrosive and toxic at high concentrations.

  • Aldehydes (glutaraldehye). These have wide germicidal activity, and are sporicidal and fungicidal. They are moderately toxic and also have a strong, unpleasant odor.

Surface Disinfectants and Resistance

Concerns have been raised by the resistance of microbes to use ofdisinfectants.1 This research relates exclusively to high-leveldisinfection, such as hospital theater standards, and are unlikely to be ofconcern in other environmental situations. Additionally, the disinfectantsconcerned were based on single active ingredients.

Traditionally, surface disinfection has been considered less important andless significant than instrument processing or waterline sanitation. However,surface areas are a prime source for indirect or secondary transmission ofinfectious diseases for both medical personnel and patients. Constant contact ofsurfaces and other environmental elements by HCWs providing medical care createopportunistic chances of cross contamination and infection. The recommendedprocedure for using disinfectants is to thoroughly clean the surface first andthen apply the disinfectant.

If microbes escape and live after a disinfectant is used, it is not becausethe pathogen is a mutant. Because disinfectants are non-selective, they kill themicrobes on contact. It is possible to miss microbes with disinfectants. Themicrobes live and continue to multiply and contaminate. The only way microbescould escape death after coming in contact with the disinfectant is if theysomehow could armor themselves so as not to have their cell membrane permeated.This is unlikely. If we are worried about the development of super, mutantbacteria, we aren't going to find the problem in the overuse of disinfectants ormany pesticides. We will find the problem in the overuse of antibiotics, somepesticides, and antibacterial products made for the use of the general public.

Rodney Stine is president of OSHA Review in Sacramento, Calif.