Controlling Microbial Growth

Action of Chemical Agents

Chemical agents work by damaging cellular structures, including proteins, cell walls and membranes, and nucleic acids.

Chemical agents are used in both sterilization for the complete elimination of microbes and in disinfection for the reduction in the number of microbes on a surface or in a fluid. Chemical agents damage cellular structures, including, but not limited to, proteins, cell walls and membranes, and nucleic acids.

Denaturation describes the process of unfolding the protein's shape, rendering it unfunctional. Chemical agents that affect proteins often do so by denaturing them. Denaturation affects the shape of the protein but not the sequence of the amino acids that make it up. However, because proteins rely on their shape in order to properly function, denaturation can bring cellular processes to a halt. Some chemical agents permanently alter the structure of the protein, making the agents germicidal. Others, however, alter the structure of the protein only when present and the protein can refold into its normal structure once the chemical agent is removed. These agents are microbiostatic, meaning they pause microbial growth but once the agent is removed the microbes will begin to grow again.

Protein Denaturation

Denaturation happens when the secondary or tertiary structure of a protein is altered, changing the protein shape. Denaturation causes the protein to become nonfunctional, causing damage or death to microbes. The colors represent the four distinct regions of the same protein.
Damage to cell walls and membranes can take varying forms. Proteins are embedded in cell membranes, so some chemical agents that damage cell membranes do so by denaturing embedded proteins. Cell membranes are primarily made up of lipids, which are held together via hydrophobic interactions. These interactions create surface tension, which keeps the cell's shape. A surfactant is a chemical agent that reduces surface tension. Surfactants make it impossible for the lipids of a cell membrane to remain in contact with one another, causing cell membrane rupture and cell breakdown. They also cause individual microbes within a colony to move away from each other, which allows other chemical agents to penetrate the cells. Because of this, surfactants can have more than one mechanism of action at once.

Chemical agents may also affect nucleic acids. Many chemical agents bind to nucleic acids or replace them in DNA and RNA sequences. This interferes with cell division and with the production of functional proteins. Chemical agents may also interrupt cellular pathways, especially those involved in cellular respiration and fermentation. This disrupts the cell's energy production, leading to cell death.