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Controlling Growth with Chemical Agents
©2000 Kenneth Todar, University of Wisconsin-Madison
Antimicrobial agents are chemicals that kill or inhibit the growth microorganisms. Antimicrobial agents include chemical preservatives and antiseptics, as well as drugs used in the treatment of infectious diseases of plants and animals. Antimicrobial agents may be of natural or synthetic origin, and they may have a static or cidal effect on microorganisms.
Types of antimicrobial agents
Antiseptics: microbicidal agents harmless enough to be applied to the skin and mucous membrane; should not be taken internaslly. Examples: mercurials, silver nitrate, iodine solution, alcohols, detergents.
Disinfectants: Agents that kill microorganisms, but not necessarily their spores,not safe for application to living tissues; they are used on inanimate objects such as tables, floors, utensils, etc. Examples: chlorine, hypochlorites, chlorine compounds, lye, copper sulfate, quaternary ammonium compounds.
Note: disinfectants and antiseptics are distinguished on the basis of whether they are safe for application to mucous membranes. Often, safety depends on the concentration of the compound. For example, sodium hypochlorite (chlorine), as added to water is safe for drinking, but "chlorox" , an excellent disinfectant, is hardly safe to drink.
Common antiseptics and disinfectants and their uses are summarized in Table 2.
Table 2. Common antiseptics and disinfectants| Chemical | Action | Uses |
|---|---|---|
| Ethanol (50-70%) | Denatures proteins and solubilizes lipids | Antiseptic used on skin |
| Isopropanol (50-70%) | Denatures proteins and solubilizes lipids | Antiseptic used on skin |
| Formaldehyde (8%) | Reacts with NH2, SH and COOH groups | Disinfectant, kills endospores |
| Tincture of Iodine (2% I2 in 70% alcohol) | Inactivates proteins | Antiseptic used on skin |
| Chlorine (Cl2) gas | Forms hypochlorous acid (HClO), a strong oxidizing agent | Disinfect drinking water; general disinfectant |
| Silver nitrate (AgNO3) | Precipitates proteins | General antiseptic and used in the eyes of newborns |
| Mercuric chloride | Inactivates proteins by reacting with sulfide groups | Disinfectant, although occasionally used as an antiseptic on skin |
| Detergents (e.g. quaternary ammonium compounds) | Disrupts cell membranes | Skin antiseptics and disinfectants |
| Phenolic compounds(e.g. carboloic acid, lysol, hexylresorcinol, hexachlorophene) | Denature proteins and disrupt cell membranes | Antiseptics at low concentrations; disinfectants at high concentrations |
| Ethylene oxide gas | Alkylating agent | Disinfectant used to sterilize heat-sensitive objects such as rubber and plastics |
Preservatives: static agents used to inhibit the growth of microorganisms, most often in foods. If eaten they should be nontoxic. Examples; calcium propionate, sodium benzoate, formaldehyde, nitrate, sulfur dioxide. Table 3 is a list of common preservative and their uses.
Table 3. Common food preservatives and their uses| Preservative | Effective Concentration | Uses |
|---|---|---|
| Propionic acid and propionates | 0.32% | Antifungal agent in breads, cake, Swiss cheeses |
| Sorbic acid and sorbates | 0.2% | Antifungal agent in cheeses, jellies, syrups, cakes |
| Benzoic acid and benzoates | 0.1% | Antifungal agent in margarine, cider, relishes, soft drinks |
| Sodium diacetate | 0.32% | Antifungal agent in breads |
| Lactic acid | ? | Antimicrobial agent in cheeses, buttermilk, yogurt and pickled foods |
| Sulfur dioxide, sulfites | 200-300 ppm | Antimicrobial agent in dried fruits, grapes, molasses |
| Sodium nitrite | 200 ppm | Antibacterial agent in cured meats, fish |
| Sodium chloride | ? | Prevents microbial spoilage of meats, fish, etc. |
| Sugar | ? | Prevents microbial spoilage of preserves, jams, syrups, jellies, etc. |
| Wood smoke | NA | Prevents microbial spoilage of meats, fish, etc. |
