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Spring 2001 - Article 6

Disinfectant News
Tackling the Resistance Issue

From time to time we are asked if bacteria and viruses can develop resistance to disinfectants, especially quats. This is a complicated issue that doesn't have a cut and dry answer. But we'll try to shed some light on it with the information we know.

Microorganisms are constantly adapting and changing to "survive" in a given environment. We can state with certainty that bacteria and viruses have developed antibiotic (drug) resistance since the introduction of penicillin in the 1930's. What we don't know is how this relates to disinfectant resistance. This is because antibiotics and disinfectants work in fundamentally different ways.

Antibiotics target a specific type of bacteria or virus and usually work within the cell to kill it. For example, erythromycin attacks ribosomes, structures within a cell that enable it to make proteins. Erythromycin-resistant bacteria have slightly altered ribosomes to which the drug cannot bind and therefore cannot kill.

On the other hand, disinfectants are not selective but rather broad-spectrum. Quats carry a positive charge (cationic). Bacteria and viruses carry a negative charge. When a bacteria-laden surface is sprayed or mopped with a quat, the charge distribution of the bacteria cell changes from negative to positive. This results in the disruption of the bacteria cell wall and eventual death to the microbe.

Since disinfectants are broad-spectrum in application, it is much harder for bacteria to develop resistance to them. To use an analogy, antibiotics work by opening a door with a key (selective). Disinfectants open the same door with a sledgehammer (non-selective).

This doesn't mean all disinfectants will kill all organisms or that the organisms can't develop resistance. We know that quats do not kill TB, spores and certain gram-negative pathogens, so we must use a different disinfectant. We also know that bacteria develop biofilms (a slimy layer secreted by a colony of bacteria) to protect themselves from the environment and chemicals. Quats are ineffective at penetrating most biofilms. This is why a pre-cleaning step with good agitation to remove biofilms is critical to proper disinfecting and sanitizing.

So, in conclusion, bacteria and viruses are much more susceptible to developing antibiotic resistance than they are to developing disinfectant resistance. And remember, don't confuse antibiotic with disinfectant resistance.