Review of Chemicals Used to Control Microbial Growth: Videos & Practice Problems

The main types of liquid chemicals used to control microbial growth include alcohols, aldehydes, biguanides, halogens, surfactants, heavy metals, phenolics, and peroxygens. Alcohols, such as ethanol and isopropanol, are effective disinfectants. Aldehydes, like formaldehyde and glutaraldehyde, are potent sterilizers. Biguanides, such as chlorhexidine, are used in antiseptics. Halogens, including chlorine and iodine, are used for disinfection and antisepsis. Surfactants, like soaps, detergents, and quats, help in cleaning and some have antimicrobial properties. Heavy metals, such as silver and copper, have antimicrobial effects. Phenolics, derived from phenol, are used in disinfectants. Peroxygens, like hydrogen peroxide and peracetic acid, are strong oxidizing agents used for sterilization.

Alcohols control microbial growth primarily by denaturing proteins and disrupting cell membranes. Common alcohols used for this purpose include ethanol and isopropanol. These alcohols are effective against a wide range of microorganisms, including bacteria, fungi, and viruses. They work best at concentrations between 60-90%, as higher concentrations can lead to rapid coagulation of proteins, which can protect the microorganisms. Alcohols are commonly used in hand sanitizers, disinfectants, and antiseptics due to their rapid action and effectiveness.

Quats, or quaternary ammonium compounds, are a type of cationic detergent with antimicrobial properties. They work by disrupting microbial cell membranes, leading to cell lysis and death. Quats are effective against a broad spectrum of microorganisms, including bacteria, fungi, and viruses. They are commonly used in disinfectants and sanitizers, especially in food preparation areas, as they are deemed safe for such environments. Quats are also used in healthcare settings for surface disinfection and in various cleaning products.

Soaps and detergents are both surfactants but differ in their composition and action. Soaps are natural surfactants made from fatty acids and a salt, such as sodium or potassium. They are not antimicrobial but act as degermers by removing microbes from surfaces. Soaps can form soap scum in hard water. Detergents, on the other hand, are synthetic surfactants that do not contain fatty acids and often have sulfonate groups. They do not form soap scum in hard water and can have antimicrobial properties, especially quats, which are a type of cationic detergent.

Gaseous chemicals used to control microbial growth include ethylene oxide, formaldehyde, and ozone. Ethylene oxide is a potent sterilizer used for medical equipment and instruments that cannot withstand high temperatures. It requires controlled conditions due to its flammability and potential explosiveness. Formaldehyde gas is used for sterilizing and disinfecting enclosed spaces and equipment. Ozone, an unstable form of oxygen, is a strong oxidizing agent used for water treatment and air disinfection. These gaseous chemicals are effective in sterilizing and disinfecting areas and items that are difficult to treat with liquid chemicals.