Microbiology, 2021

13.3 • Using Chemicals to Control Microorganisms 529
Figure 13.18
13.3 Using Chemicals to Control Microorganisms
Learning Objectives
By the end of this section, you will be able to:
• Understand and compare various chemicals used to control microbial growth, including their uses,
advantages and disadvantages, chemical structure, and mode of action
In addition to physical methods of microbial control, chemicals are also used to control microbial growth. A
wide variety of chemicals can be used as disinfectants or antiseptics. When choosing which to use, it is
important to consider the type of microbe targeted; how clean the item needs to be; the disinfectant’s effect on
the item’s integrity; its safety to animals, humans, and the environment; its expense; and its ease of use. This
section describes the variety of chemicals used as disinfectants and antiseptics, including their mechanisms
of action and common uses.
Phenolics
In the 1800s, scientists began experimenting with a variety of chemicals for disinfection. In the 1860s, British
surgeon Joseph Lister (1827–1912) began using carbolic acid, known as phenol, as a disinfectant for the
treatment of surgical wounds (see Foundations of Modern Cell Theory). In 1879, Lister’s work inspired the
American chemist Joseph Lawrence (1836–1909) to develop Listerine, an alcohol-based mixture of several
related compounds that is still used today as an oral antiseptic. Today, carbolic acid is no longer used as a
surgical disinfectant because it is a skin irritant, but the chemical compounds found in antiseptic
mouthwashes and throat lozenges are called phenolics.
Chemically, phenol consists of a benzene ring with an –OH group, and phenolics are compounds that have this
group as part of their chemical structure (Figure 13.19). Phenolics such as thymol and eucalyptol occur
naturally in plants. Other phenolics can be derived from creosote, a component of coal tar. Phenolics tend to be
stable, persistent on surfaces, and less toxic than phenol. They inhibit microbial growth by denaturing proteins
and disrupting membranes.