Phenol (carbolic acid) is important historically because it was one of the earliest disinfectants, but its use is now limited because it has an unpleasant odor and irritates the skin. A group of structurally related compounds, however, have increased ger-micidal activity, which enables effective use of more dilute and therefore less irritating solutions. Phenolic compounds are the active ingredients in Lysol™.
Phenolics destroy cytoplasmic membranes of microorganisms and denature proteins. They kill most vegetative bacteria and, in high concentrations (from 5% to 19%), many can kill Mycobacterium tuberculosis. They do not, however, reliably inactivate all groups of viruses. The major advantages of phenolic
5.4 Using Chemicals to Destroy Microorganisms and Viruses 121
PERSPECTIVE 5.1 Contamination of an Operating Room by a Bacterial Pathogen
A patient with burns infected with Pseudomonas aeruginosa was taken to the operating room for cleaning of the wounds and removal of dead tissue. After the procedure was completed, samples of various surfaces in the room were cultured to determine the extent of contamination. P. aeruginosa was recovered from all parts of the room. Figure 1 shows how readily and extensively an operating room can become contaminated by an infected patient. Operating rooms and other patient care rooms must be thoroughly cleaned after use, in a process known as terminal cleaning.
compounds include their wide range of activity, reasonable cost, and ability to remain effective in the presence of detergents and organic contaminants. They also leave an active antimicrobial residue, which in some cases is desirable.
Some phenolics, such as triclosan and hexachlorophene, are sufficiently non-toxic to be used in soaps and lotions. Triclosan is widely used as an ingredient in a variety of personal care products such as deodorant soaps, lotions, and toothpaste. Hexachlorophene has substantial activity against Staphylococcus aureus, the leading cause of wound infections, but high levels have been associated with symptoms of neurotoxicity. Although once widely used in hospitals, antiseptic skin cleansers containing hexachlorophene are now available only with a prescription.
Quaternary Ammonium Compounds (Quats)
Quaternary ammonium compounds, also commonly called quats, are cationic (positively charged) detergents that are non-toxic enough to be used to disinfect food preparation surfaces. Like all detergents, quats have both a charged hydrophilic region and an uncharged hydrophobic region. This enables them to reduce the surface tension of liquids and help wash away dirt and organic material, facilitating the mechanical removal of microorganisms from surfaces. Unlike most common household soaps and detergents, however, which are anionic (negatively charged) and repelled by the negatively charged microbial cell surface, quats are attracted to the cell sur face. They react with membranes, destroying many vegetative bacteria and enveloped viruses. They are not effective, however, against endospores, mycobacteria, or naked viruses.
Quaternary ammonium compounds are economical and effective agents that are widely used to disinfect clean inanimate objects and to preserve non-food substances. The ingredients of many personal care products include quats such as benzalkoni-um chloride or cetylpyridinium chloride. They also enhance the effectiveness of some other disinfectants. Cationic soaps and organic material such as gauze, however, can neutralize their effectiveness. In addition, Pseudomonas, a troublesome cause of nosocomial infections, resists the effects of quats and can even grow in solutions preserved with them.
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