Selective toxicity

What is selective toxicity?

In the context of microbiology, selective toxicity is the idea that a chemical agent or drug can exert a toxic effect on a pathogen and leave the infected host organism unharmed.

Antimicrobial drugs such as penicillin, metronidazole and chloramphenicol interact with cellular components that are only found in their target organism. This allows the agent to exert its effect only on the cells that carry the target component, for example, an enzyme involved in building a cell wall or a specific metabolic ribozyme.

Becoming resistant

As microorganisms mutate, changes to the target component may occur meaning the drug may no longer exert its toxic effect. If the antimicrobial agent is present and actively killing off unmutated competing sister cells at the time, the mutated cell may have a survival advantage.

The proliferation of mutant cells can lead to antimicrobial resistance which can worsen should the resistant gene be transferred to other microorganisms.


A summary of different agent types and their selectively toxic features is shown below:

Table with four rows and three columns named: “Type of agent”, “Selective toxic”, and “Target”. First agent, disinfectant, is not selectively toxic and targets all proteins, lipids, organic compounds etc. Second agent, antiseptic, is not selectively toxic, targets all proteins, lipids, organic compounds etc., and is safe for external use on skin. Third agent, antimicrobial, is selectively toxic, binds or is activated by a specific target found only in the target organism, and is safe for internal administration.