Microbiology, 2021

13.3 • Using Chemicals to Control Microorganisms 541
MICRO CONNECTIONS
Diehard Prions
Prions, the acellular, misfolded proteins responsible for incurable and fatal diseases such as kuru and
Creutzfeldt-Jakob disease (see Viroids, Virusoids, and Prions), are notoriously difficult to destroy. Prions are
extremely resistant to heat, chemicals, and radiation. They are also extremely infectious and deadly; thus,
handling and disposing of prion-infected items requires extensive training and extreme caution.
Typical methods of disinfection can reduce but not eliminate the infectivity of prions. Autoclaving is not
completely effective, nor are chemicals such as phenol, alcohols, formalin, and β-propiolactone. Even when
fixed in formalin, affected brain and spinal cord tissues remain infectious.
Personnel who handle contaminated specimens or equipment or work with infected patients must wear a
protective coat, face protection, and cut-resistant gloves. Any contact with skin must be immediately washed
with detergent and warm water without scrubbing. The skin should then be washed with 1 N NaOH or a 1:10
dilution of bleach for 1 minute. Contaminated waste must be incinerated or autoclaved in a strong basic
solution, and instruments must be cleaned and soaked in a strong basic solution.
LINK TO LEARNING
For more information on the handling of animals and prion-contaminated materials, visit the guidelines
published on the WHO (https://openstax.org/l/22WHOhandanipri) website.
Peroxygens
Peroxygens are strong oxidizing agents that can be used as disinfectants or antiseptics. The most widely used
peroxygen is hydrogen peroxide (H 2 O 2 ), which is often used in solution to disinfect surfaces and may also be
used as a gaseous agent. Hydrogen peroxide solutions are inexpensive skin antiseptics that break down into
water and oxygen gas, both of which are environmentally safe. This decomposition is accelerated in the
presence of light, so hydrogen peroxide solutions typically are sold in brown or opaque bottles. One
disadvantage of using hydrogen peroxide as an antiseptic is that it also causes damage to skin that may delay
healing or lead to scarring. Contact lens cleaners often include hydrogen peroxide as a disinfectant.
Hydrogen peroxide works by producing free radicals that damage cellular macromolecules. Hydrogen
peroxide has broad-spectrum activity, working against gram-positive and gram-negative bacteria (with slightly
greater efficacy against gram-positive bacteria), fungi, viruses, and endospores. However, bacteria that
produce the oxygen-detoxifying enzymes catalase or peroxidase may have inherent tolerance to low hydrogen
peroxide concentrations (Figure 13.30). To kill endospores, the length of exposure or concentration of
solutions of hydrogen peroxide must be increased. Gaseous hydrogen peroxide has greater efficacy and can be
used as a sterilant for rooms or equipment.
Figure 13.30
Catalase enzymatically converts highly reactive hydrogen peroxide (H 2 O 2 ) into water and oxygen. Hydrogen peroxide can be