Microbiology, 2021

534 13 • Control of Microbial Growth
Figure 13.22
(a) Betadine is a solution of the iodophor povidone-iodine. (b) It is commonly used as a topical antiseptic on a patient’s skin
before incision during surgery. (credit b: modification of work by Andrew Ratto)
Chlorine is another halogen commonly used for disinfection. When chlorine gas is mixed with water, it
produces a strong oxidant called hypochlorous acid, which is uncharged and enters cells easily. Chlorine gas is
commonly used in municipal drinking water and wastewater treatment plants, with the resulting
hypochlorous acid producing the actual antimicrobial effect. Those working at water treatment facilities need
to take great care to minimize personal exposure to chlorine gas. Sodium hypochlorite is the chemical
component of common household bleach, and it is also used for a wide variety of disinfecting purposes.
Hypochlorite salts, including sodium and calcium hypochlorites, are used to disinfect swimming pools.
Chlorine gas, sodium hypochlorite, and calcium hypochlorite are also commonly used disinfectants in the food
processing and restaurant industries to reduce the spread of foodborne diseases. Workers in these industries
also need to take care to use these products correctly to ensure their own safety as well as the safety of
consumers. A recent joint statement published by the Food and Agriculture Organization (FAO) of the United
Nations and WHO indicated that none of the many beneficial uses of chlorine products in food processing to
reduce the spread of foodborne illness posed risks to consumers. 18
Another class of chlorinated compounds called chloramines are widely used as disinfectants. Chloramines are
relatively stable, releasing chlorine over long periods time. Chloramines are derivatives of ammonia by
substitution of one, two, or all three hydrogen atoms with chlorine atoms (Figure 13.23).
Figure 13.23
chlorine atom.
Monochloroamine, one of the chloramines, is derived from ammonia by the replacement of one hydrogen atom with a
Chloramines and other cholorine compounds may be used for disinfection of drinking water, and chloramine
tablets are frequently used by the military for this purpose. After a natural disaster or other event that
compromises the public water supply, the CDC recommends disinfecting tap water by adding small amounts of
regular household bleach. Recent research suggests that sodium dichloroisocyanurate (NaDCC) may also be a
good alternative for drinking water disinfection. Currently, NaDCC tablets are available for general use and for
use by the military, campers, or those with emergency needs; for these uses, NaDCC is preferable to
chloramine tablets. Chlorine dioxide, a gaseous agent used for fumigation and sterilization of enclosed areas,
is also commonly used for the disinfection of water.
Although chlorinated compounds are relatively effective disinfectants, they have their disadvantages. Some
may irritate the skin, nose, or eyes of some individuals, and they may not completely eliminate certain hardy
organisms from contaminated drinking water. The protozoan parasite Cryptosporidium, for example, has a
18 World Health Organization. “Benefits and Risks of the Use of Chlorine-Containing Disinfectants in Food Production and Food
Processing: Report of a Joint FAO/WHO Expert Meeting.” Geneva, Switzerland: World Health Organization, 2009.
Access for free at openstax.org.