what chemical cycle uses bacteria to fix gases from the air

Learning Objectives

• Understand and compare diverse chemicals used to control microbial growth, including their uses, advantages and disadvantages, chemical structure, and mode of action

In improver to concrete methods of microbial control, chemicals are also used to control microbial growth. A wide diverseness of chemicals tin can be used as disinfectants or antiseptics. When choosing which to use, it is important to consider the blazon of microbe targeted; how make clean the particular needs to be; the disinfectant's effect on the item's integrity; its condom to animals, humans, and the environment; its expense; and its ease of use. This section describes the diversity of chemicals used as disinfectants and antiseptics, including their mechanisms of activeness and common uses.

Phenolics

In the 1800s, scientists began experimenting with a diverseness of chemicals for disinfection. In the 1860s, British surgeon Joseph Lister (1827–1912) began using carbolic acid, known equally phenol, as a disinfectant for the handling of surgical wounds (encounter Foundations of Modern Cell Theory). In 1879, Lister's piece of work inspired the American chemist Joseph Lawrence (1836–1909) to develop Listerine, an alcohol-based mixture of several related compounds that is notwithstanding used today equally an oral antiseptic. Today, carbolic acid is no longer used equally a surgical disinfectant because information technology is a pare irritant, but the chemical compounds institute in clarified mouthwashes and throat lozenges are called phenolics.

Chemically, phenol consists of a benzene ring with an –OH group, and phenolics are compounds that have this group equally role of their chemical structure. Phenolics such every bit thymol and eucalyptol occur naturally in plants. Other phenolics tin can be derived from creosote, a component of coal tar. Phenolics tend to be stable, persistent on surfaces, and less toxic than phenol. They inhibit microbial growth past denaturing proteins and disrupting membranes.

Figure 1. Phenol and phenolic compounds have been used to control microbial growth. (a) Chemic structure of phenol, also known as carbolic acid. (b) o-Phenylphenol, a type of phenolic, has been used as a disinfectant too as to control bacterial and fungal growth on harvested citrus fruits. (c) Hexachlorophene, another phenol, known as a bisphenol (two rings), is the active ingredient in pHisoHex.

Since Lister'due south fourth dimension, several phenolic compounds take been used to control microbial growth. Phenolics like cresols (methylated phenols) and o-phenylphenol were active ingredients in various formulations of Lysol since its invention in 1889. o-Phenylphenol was as well commonly used in agriculture to control bacterial and fungal growth on harvested crops, especially citrus fruits, simply its utilize in the The states is now far more limited. The bisphenol hexachlorophene, a disinfectant, is the agile ingredient in pHisoHex, a topical cleansing detergent widely used for handwashing in hospital settings. pHisoHex is particularly effective confronting gram-positive bacteria, including those causing staphylococcal and streptococcal pare infections. pHisoHex was formerly used for bathing infants, but this do has been discontinued because information technology has been shown that exposure to hexachlorophene can lead to neurological issues.

Triclosan is another bisphenol compound that has seen widespread awarding in antibacterial products over the final several decades. Initially used in toothpastes, triclosan is now usually used in hand soaps and is frequently impregnated into a wide variety of other products, including cutting boards, knives, shower curtains, wear, and physical, to make them antimicrobial. It is particularly effective against gram-positive bacteria on the skin, as well equally certain gram-negative bacteria and yeasts.^[1]

Triclosan: Antibacterial Overkill?

Hand soaps and other cleaning products are oft marketed equally "antibacterial," suggesting that they provide a level of cleanliness superior to that of conventional soaps and cleansers. But are the antibacterial ingredients in these products really rubber and effective?

About 75% of antibacterial liquid hand soaps and 30% of bar soaps comprise the chemical triclosan, a phenolic.^[ii] Triclosan blocks an enzyme in the bacterial fatty acid-biosynthesis pathway that is not found in the comparable human pathway. Although the use of triclosan in the home increased dramatically during the 1990s, more than forty years of research by the FDA take turned upward no conclusive bear witness that washing with triclosan-containing products provides increased wellness benefits compared with washing with traditional soap. Although some studies signal that fewer bacteria may remain on a person's hands later washing with triclosan-based soap, compared with traditional soap, no prove points to any reduction in the transmission of leaner that cause respiratory and gastrointestinal disease. In short, soaps with triclosan may remove or kill a few more germs but not enough to reduce the spread of disease.

Perhaps more disturbing, some clear risks associated with triclosan-based soaps accept come up to light. The widespread use of triclosan has led to an increase in triclosan-resistant bacterial strains, including those of clinical importance, such as Salmonella enterica; this resistance may return triclosan useless as an antibacterial in the long run.^{[3] [4]} Bacteria can hands proceeds resistance to triclosan through a change to a single gene encoding the targeted enzyme in the bacterial fatty acid-synthesis pathway. Other disinfectants with a less specific way of action are much less prone to engendering resistance because information technology would accept much more than a single genetic alter.

Employ of triclosan over the last several decades has too led to a buildup of the chemical in the environment. Triclosan in mitt soap is directly introduced into wastewater and sewage systems as a effect of the handwashing procedure. There, its antibacterial backdrop can inhibit or impale bacteria responsible for the decomposition of sewage, causing septic systems to clog and back up. Eventually, triclosan in wastewater finds its way into surface waters, streams, lakes, sediments, and soils, disrupting natural populations of bacteria that carry out important environmental functions, such as inhibiting algae. Triclosan also finds its fashion into the bodies of amphibians and fish, where it can human action as an endocrine disruptor. Detectable levels of triclosan have also been found in various man bodily fluids, including chest milk, plasma, and urine.^[5] In fact, a study conducted by the CDC found detectable levels of triclosan in the urine of 75% of 2,517 people tested in 2003–2004.^[6] This finding is even more troubling given the evidence that triclosan may affect allowed function in humans.^[7]

In December 2013, the FDA gave soap manufacturers until 2016 to prove that antibacterial soaps provide a meaning benefit over traditional soaps; if unable to do then, manufacturers will be forced to remove these products from the market.

Effigy 2. Triclosan is a common ingredient in antibacterial soaps despite show that it poses ecology and health risks and offers no pregnant wellness benefit compared to conventional soaps. (credit b, c: modification of work by FDA)

Think About Information technology

• Why is triclosan more like an antibody than a traditional disinfectant?

Heavy Metals

Some of the outset chemical disinfectants and antiseptics to be used were heavy metals. Heavy metals kill microbes by bounden to proteins, thus inhibiting enzymatic activeness. Heavy metals are oligodynamic, meaning that very small concentrations show significant antimicrobial activity. Ions of heavy metals demark to sulfur-containing amino acids strongly and bioaccumulate within cells, assuasive these metals to reach loftier localized concentrations. This causes proteins to denature.

Heavy metals are not selectively toxic to microbial cells. They may bioaccumulate in human or animal cells, too, and excessive concentrations tin can have toxic effects on humans. If too much silver accumulates in the body, for case, it tin can result in a condition chosen argyria, in which the skin turns irreversibly blue-gray. 1 way to reduce the potential toxicity of heavy metals is past carefully controlling the duration of exposure and concentration of the heavy metal.

Figure iii. Heavy metals denature proteins, impairing cell function and, thus, giving them potent antimicrobial properties. (a) Copper in fixtures like this door handle kills microbes that otherwise might accumulate on frequently touched surfaces. (b) Eating utensils contain pocket-sized amounts of argent to inhibit microbial growth. (c) Copper commonly lines incubators to minimize contamination of jail cell cultures stored inside. (d) Antiseptic mouthwashes commonly incorporate zinc chloride. (e) This patient is suffering from argyria, an irreversible status caused past bioaccumulation of silverish in the trunk. (credit b: modification of work past "Shoshanah"/Flickr; credit e: modification of piece of work by Herbert L. Fred and Hendrik A. van Dijk)

Mercury

Mercury is an case of a heavy metallic that has been used for many years to command microbial growth. It was used for many centuries to care for syphilis. Mercury compounds like mercuric chloride are mainly bacteriostatic and have a very broad spectrum of activeness. Various forms of mercury bind to sulfur-containing amino acids inside proteins, inhibiting their functions.

In recent decades, the use of such compounds has diminished because of mercury's toxicity. It is toxic to the central nervous, digestive, and renal systems at high concentrations, and has negative environmental effects, including bioaccumulation in fish. Topical antiseptics such as mercurochrome, which contains mercury in low concentrations, and merthiolate, a tincture (a solution of mercury dissolved in alcohol) were once commonly used. However, because of concerns almost using mercury compounds, these antiseptics are no longer sold in the The states.

Silver

Silver has long been used as an antiseptic. In ancient times, drinking water was stored in silver jugs.^[8] Silvadene cream is usually used to treat topical wounds and is particularly helpful in preventing infection in burn wounds. Silver nitrate drops were one time routinely applied to the optics of newborns to protect against ophthalmia neonatorum, heart infections that can occur due to exposure to pathogens in the birth canal, just antibiotic creams are more at present commonly used. Silvery is often combined with antibiotics, making the antibiotics thousands of times more effective.^[9] Silver is also usually incorporated into catheters and bandages, rendering them antimicrobial; however, there is evidence that heavy metals may likewise raise selection for antibody resistance.^[10]

Copper, Nickel, and Zinc

Several other heavy metals as well exhibit antimicrobial activity. Copper sulfate is a common algaecide used to command algal growth in swimming pools and fish tanks. The utilize of metal copper to minimize microbial growth is also becoming more widespread. Copper linings in incubators assistance reduce contagion of jail cell cultures. The use of copper pots for water storage in underdeveloped countries is being investigated as a way to combat diarrheal diseases. Copper coatings are also becoming popular for frequently handled objects such as doorknobs, cabinet hardware, and other fixtures in wellness-intendance facilities in an endeavour to reduce the spread of microbes.

Nickel and zinc coatings are now being used in a similar fashion. Other forms of zinc, including zinc chloride and zinc oxide, are also used commercially. Zinc chloride is quite safe for humans and is commonly found in mouthwashes, essentially increasing their length of effectiveness. Zinc oxide is found in a diverseness of products, including topical antiseptic creams such every bit calamine balm, diaper ointments, baby powder, and dandruff shampoos.

Think Almost It

• Why are many heavy metals both antimicrobial and toxic to humans?

Halogens

Other chemicals commonly used for disinfection are the halogens iodine, chlorine, and fluorine. Iodine works by oxidizing cellular components, including sulfur-containing amino acids, nucleotides, and fatty acids, and destabilizing the macromolecules that contain these molecules. Information technology is often used as a topical tincture, merely it may cause staining or skin irritation. An iodophor is a chemical compound of iodine complexed with an organic molecule, thereby increasing iodine's stability and, in plough, its efficacy. One common iodophor is povidone-iodine, which includes a wetting amanuensis that releases iodine relatively slowly. Betadine is a brand of povidone-iodine commonly used as a mitt scrub by medical personnel before surgery and for topical antisepsis of a patient'due south peel earlier incision.

Figure 4. (a) Betadine is a solution of the iodophor povidone-iodine. (b) It is commonly used every bit a topical clarified on a patient'south 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, information technology produces a strong oxidant called hypochlorous acid, which is uncharged and enters cells easily. Chlorine gas is usually used in municipal drinking water and wastewater handling plants, with the resulting hypochlorous acid producing the actual antimicrobial effect. Those working at h2o treatment facilities need to have great care to minimize personal exposure to chlorine gas. Sodium hypochlorite is the chemical component of mutual household bleach, and information technology is also used for a wide multifariousness 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 unremarkably used disinfectants in the food processing and eatery industries to reduce the spread of foodborne diseases. Workers in these industries also demand to take care to utilize these products correctly to ensure their own safety equally well every bit the safety of consumers. A recent articulation statement published by the Food and Agriculture Organization (FAO) of the Un and WHO indicated that none of the many benign uses of chlorine products in nutrient processing to reduce the spread of foodborne disease posed risks to consumers.^[11]

Another form of chlorinated compounds chosen chloramines are widely used equally disinfectants. Chloramines are relatively stable, releasing chlorine over long periods time. Chloramines are derivatives of ammonia by substitution of one, ii, or all 3 hydrogen atoms with chlorine atoms.

Figure 5. Monochloroamine, 1 of the chloramines, is derived from ammonia by the replacement of one hydrogen atom with a chlorine atom.

Chloramines and other cholorine compounds may be used for disinfection of drinking h2o, and chloramine tablets are ofttimes used by the military machine for this purpose. After a natural disaster or other event that compromises the public h2o supply, the CDC recommends disinfecting tap water by adding minor amounts of regular household bleach. Contempo research suggests that sodium dichloroisocyanurate (NaDCC) may also be a skillful alternative for drinking water disinfection. Currently, NaDCC tablets are available for general use and for use by the armed forces, 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 usually used for the disinfection of water.

Although chlorinated compounds are relatively effective disinfectants, they have their disadvantages. Some may irritate the pare, olfactory organ, or eyes of some individuals, and they may non completely eliminate certain hardy organisms from contaminated drinking water. The mucus Cryptosporidium , for example, has a protective outer shell that makes information technology resistant to chlorinated disinfectants. Thus, boiling of drinking water in emergency situations is recommended when possible.

The element of group vii fluorine is also known to have antimicrobial properties that contribute to the prevention of dental caries (cavities).^[12] Fluoride is the chief active ingredient of toothpaste and is also commonly added to tap h2o to assist communities maintain oral health. Chemically, fluoride tin go incorporated into the hydroxyapatite of tooth enamel, making it more resistant to corrosive acids produced past the fermentation of oral microbes. Fluoride likewise enhances the uptake of calcium and phosphate ions in tooth enamel, promoting remineralization. In add-on to strengthening enamel, fluoride also seems to exist bacteriostatic. It accumulates in plaque-forming bacteria, interfering with their metabolism and reducing their product of the acids that contribute to tooth decay.

Recollect Well-nigh Information technology

• What is a do good of a chloramine over hypochlorite for disinfecting?

Alcohols

Alcohols make up another group of chemicals normally used as disinfectants and antiseptics. They work by rapidly denaturing proteins, which inhibits cell metabolism, and past disrupting membranes, which leads to cell lysis. Once denatured, the proteins may potentially refold if enough water is present in the solution. Alcohols are typically used at concentrations of about 70% aqueous solution and, in fact, work improve in aqueous solutions than 100% alcohol solutions. This is because alcohols coagulate proteins. In higher booze concentrations, rapid coagulation of surface proteins prevents effective penetration of cells. The most commonly used alcohols for disinfection are ethyl alcohol (ethanol) and isopropyl booze (isopropanol, rubbing alcohol).

Alcohols tend to be bactericidal and fungicidal, just may too be viricidal for enveloped viruses simply. Although alcohols are not sporicidal, they practice inhibit the processes of sporulation and germination. Alcohols are volatile and dry chop-chop, but they may also cause peel irritation because they dehydrate the skin at the site of application. One common clinical use of alcohols is swabbing the skin for degerming before needle injection. Alcohols also are the agile ingredients in instant hand sanitizers, which take gained popularity in contempo years. The alcohol in these hand sanitizers works both by denaturing proteins and by disrupting the microbial cell membrane, just will not piece of work effectively in the presence of visible clay.

Last, alcohols are used to make tinctures with other antiseptics, such as the iodine tinctures discussed previously in this chapter. All in all, alcohols are cheap and quite effective for the disinfection of a broad range of vegetative microbes. However, i disadvantage of alcohols is their high volatility, limiting their effectiveness to immediately later on application.

Figure vi. (a) Ethyl booze, the intoxicating ingredient found in alcoholic drinks, is also used ordinarily as a disinfectant. (b) Isopropyl alcohol, besides called rubbing alcohol, has a related molecular structure and is another usually used disinfectant. (credit a photo: modification of work by D Coetzee; credit b photograph: modification of piece of work past Craig Spurrier)

Think Almost It

• Proper name at least three advantages of alcohols as disinfectants.
• Describe several specific applications of alcohols used in disinfectant products.

Surfactants

Surface-agile agents, or surfactants, are a group of chemical compounds that lower the surface tension of water. Surfactants are the major ingredients in soaps and detergents. Soaps are salts of long-chain fat acids and have both polar and nonpolar regions, allowing them to interact with polar and nonpolar regions in other molecules. They can collaborate with nonpolar oils and grease to create emulsions in h2o, loosening and lifting away dirt and microbes from surfaces and skin. Soaps exercise not kill or inhibit microbial growth and so are not considered antiseptics or disinfectants. However, proper use of soaps mechanically carries abroad microorganisms, effectively degerming a surface. Some soaps comprise added bacteriostatic agents such as triclocarban or cloflucarban, compounds structurally related to triclosan, that innovate antiseptic or disinfectant backdrop to the soaps.

Figure 7. Soaps are the salts (sodium salt in the illustration) of fat acids and have the ability to emulsify lipids, fats, and oils by interacting with water through their hydrophilic heads and with the lipid at their hydrophobic tails.

Soaps, notwithstanding, oftentimes class films that are hard to rinse away, especially in hard water, which contains high concentrations of calcium and magnesium mineral salts. Detergents contain synthetic surfactant molecules with both polar and nonpolar regions that have stiff cleansing action but are more soluble, even in difficult h2o, and, therefore, leave behind no soapy deposits. Anionic detergents, such as those used for laundry, have a negatively charged anion at one end attached to a long hydrophobic chain, whereas cationic detergents have a positively charged cation instead. Cationic detergents include an important class of disinfectants and antiseptics called the quaternary ammonium salts (quats), named for the characteristic quaternary nitrogen atom that confers the positive charge. Overall, quats have properties similar to phospholipids, having hydrophilic and hydrophobic ends. As such, quats have the ability to insert into the bacterial phospholipid bilayer and disrupt membrane integrity. The cationic accuse of quats appears to confer their antimicrobial properties, which are diminished when neutralized. Quats have several useful properties. They are stable, nontoxic, inexpensive, colorless, odorless, and tasteless. They tend to exist bactericidal past disrupting membranes. They are besides active against fungi, protozoans, and enveloped viruses, but endospores are unaffected. In clinical settings, they may exist used as antiseptics or to disinfect surfaces. Mixtures of quats are too unremarkably establish in household cleaners and disinfectants, including many current formulations of Lysol brand products, which contain benzalkonium chlorides as the agile ingredients. Benzalkonium chlorides, along with the quat cetylpyrimidine chloride, are also found in products such as skin antiseptics, oral rinses, and mouthwashes.

Figure eight. (a) Two common quats are benzylalkonium chloride and cetylpyrimidine chloride. Note the hydrophobic nonpolar carbon chain at one end and the nitrogen-containing cationic component at the other end. (b) Quats are able to infiltrate the phospholipid plasma membranes of bacterial cells and disrupt their integrity, leading to death of the prison cell.

Recall About It

• Why are soaps not considered disinfectants?

Handwashing the Right Way

Handwashing is critical for public health and should be emphasized in a clinical setting. For the full general public, the CDC recommends handwashing before, during, and after nutrient handling; before eating; earlier and later interacting with someone who is sick; before and later treating a wound; afterwards using the toilet or irresolute diapers; later on coughing, sneezing, or blowing the nose; after handling garbage; and after interacting with an fauna, its feed, or its waste. Figure ix illustrates the five steps of proper handwashing recommended by the CDC.

Handwashing is fifty-fifty more important for health-care workers, who should wash their hands thoroughly between every patient contact, after the removal of gloves, later on contact with bodily fluids and potentially infectious fomites, and before and after assisting a surgeon with invasive procedures. Even with the use of proper surgical attire, including gloves, scrubbing for surgery is more involved than routine handwashing. The goal of surgical scrubbing is to reduce the normal microbiota on the skin's surface to prevent the introduction of these microbes into a patient'south surgical wounds.

There is no unmarried widely accepted protocol for surgical scrubbing. Protocols for length of fourth dimension spent scrubbing may depend on the antimicrobial used; wellness-care workers should e'er check the manufacturer's recommendations. According to the Association of Surgical Technologists (AST), surgical scrubs may be performed with or without the apply of brushes.

Effigy 9. (a) The CDC recommends five steps as part of typical handwashing for the general public. (b) Surgical scrubbing is more extensive, requiring scrubbing starting from the fingertips, extending to the hands and forearms, and then upwardly across the elbows, equally shown hither. (credit a: modification of piece of work by World Health Organization)

To acquire more about proper handwashing, visit the CDC'due south website.

Bisbiguanides

Bisbiguanides were first synthesized in the 20th century and are cationic (positively charged) molecules known for their antiseptic properties. Ane important bisbiguanide antiseptic is chlorhexidine. It has broad-spectrum activeness against yeasts, gram-positive leaner, and gram-negative bacteria, with the exception of Pseudomonas aeruginosa , which may develop resistance on repeated exposure.^[13] Chlorhexidine disrupts cell membranes and is bacteriostatic at lower concentrations or bactericidal at higher concentrations, in which it actually causes the cells' cytoplasmic contents to ossify. It too has activity against enveloped viruses. However, chlorhexidine is poorly effective against Mycobacterium tuberculosis and nonenveloped viruses, and it is not sporicidal. Chlorhexidine is typically used in the clinical setting as a surgical scrub and for other handwashing needs for medical personnel, every bit well as for topical antisepsis for patients before surgery or needle injection. It is more than persistent than iodophors, providing long-lasting antimicrobial activity. Chlorhexidine solutions may also be used as oral rinses after oral procedures or to treat gingivitis. Another bisbiguanide, alexidine, is gaining popularity as a surgical scrub and an oral rinse considering it acts faster than chlorhexidine.

Figure x. The bisbiguanides chlorhexadine and alexidine are cationic antiseptic compounds commonly used as surgical scrubs.

Think About It

• What ii furnishings does chlorhexidine have on bacterial cells?

Alkylating Agents

The alkylating agents are a group of strong disinfecting chemicals that act by replacing a hydrogen atom within a molecule with an alkyl group (C_northwardH_2n+1), thereby inactivating enzymes and nucleic acids. The alkylating amanuensis formaldehyde (CH₂OH) is commonly used in solution at a concentration of 37% (known every bit formalin) or as a gaseous disinfectant and biocide. It is a strong, broad-spectrum disinfectant and biocide that has the power to kill bacteria, viruses, fungi, and endospores, leading to sterilization at low temperatures, which is sometimes a convenient alternative to the more labor-intensive rut sterilization methods. It likewise cantankerous-links proteins and has been widely used equally a chemical fixative. Because of this, it is used for the storage of tissue specimens and every bit an embalming fluid. It as well has been used to inactivate infectious agents in vaccine preparation. Formaldehyde is very irritating to living tissues and is also carcinogenic; therefore, it is not used equally an clarified.

Glutaraldehyde is structurally similar to formaldehyde but has ii reactive aldehyde groups, allowing it to act more than quickly than formaldehyde. It is commonly used every bit a 2% solution for sterilization and is marketed nether the brand proper name Cidex. Information technology is used to disinfect a variety of surfaces and surgical and medical equipment. Even so, similar to formaldehyde, glutaraldehyde irritates the skin and is not used equally an clarified.

A new type of disinfectant gaining popularity for the disinfection of medical equipment is o-phthalaldehyde (OPA), which is found in some newer formulations of Cidex and similar products, replacing glutaraldehyde. o-Phthalaldehyde also has 2 reactive aldehyde groups, simply they are linked by an aromatic span. o-Phthalaldehyde is idea to work similarly to glutaraldehyde and formaldehyde, but is much less irritating to skin and nasal passages, produces a minimal odor, does not require processing before use, and is more constructive confronting mycobacteria.

Ethylene oxide is a type of alkylating agent that is used for gaseous sterilization. It is highly penetrating and tin can sterilize items inside plastic bags such equally catheters, disposable items in laboratories and clinical settings (similar packaged Petri dishes), and other pieces of equipment. Ethylene oxide exposure is a form of cold sterilization, making it useful for the sterilization of heat-sensitive items. Dandy care needs to be taken with the use of ethylene oxide, however; information technology is carcinogenic, like the other alkylating agents, and is also highly explosive. With careful utilize and proper aeration of the products after treatment, ethylene oxide is highly effective, and ethylene oxide sterilizers are ordinarily constitute in medical settings for sterilizing packaged materials.

β-Propionolactone is an alkylating amanuensis with a different chemical structure than the others already discussed. Like other alkylating agents, β-propionolactone binds to Dna, thereby inactivating it. It is a clear liquid with a stiff smell and has the ability to kill endospores. Equally such, it has been used in either liquid class or equally a vapor for the sterilization of medical instruments and tissue grafts, and it is a common component of vaccines, used to maintain their sterility. Information technology has also been used for the sterilization of nutrient broth, as well as blood plasma, milk, and water. It is apace metabolized by animals and humans to lactic acid. It is besides an irritant, still, and may pb to permanent harm of the eyes, kidneys, or liver. Additionally, information technology has been shown to be carcinogenic in animals; thus, precautions are necessary to minimize human being exposure to β-propionolactone.^[14]

Figure 11. (a) Alkylating agents supercede hydrogen atoms with alkyl groups. Here, guanine is alkylated, resulting in its hydrogen bonding with thymine, instead of cytosine. (b) The chemical structures of several alkylating agents.

Think About It

• What chemical reaction practise alkylating agents participate in?
• Why are alkylating agents not used as antiseptics?

Diehard Prions

Prions, the acellular, misfolded proteins responsible for incurable and fatal diseases such as kuru and Creutzfeldt-Jakob disease (come across Viroids, Virusoids, and Prions), are notoriously difficult to destroy. Prions are extremely resistant to estrus, chemicals, and radiation. They are as well extremely infectious and deadly; thus, treatment and disposing of prion-infected items requires extensive training and farthermost caution.

Typical methods of disinfection can reduce only non eliminate the infectivity of prions. Autoclaving is non completely constructive, nor are chemicals such every bit phenol, alcohols, formalin, and β-propiolactone. Even when fixed in formalin, affected brain and spinal string tissues remain infectious.

Personnel who handle contaminated specimens or equipment or piece of work with infected patients must wear a protective glaze, face protection, and cut-resistant gloves. Any contact with skin must be immediately done with detergent and warm h2o without scrubbing. The skin should then be washed with 1 N NaOH or a 1:10 dilution of bleach for 1 minute. Contaminated waste material must be incinerated or autoclaved in a strong basic solution, and instruments must be cleaned and soaked in a strong basic solution.

For more information on the handling of animals and prion-contaminated materials, visit the guidelines published on the CDC and WHO websites.

Peroxygens

Peroxygens are strong oxidizing agents that tin can be used as disinfectants or antiseptics. The most widely used peroxygen is hydrogen peroxide (H₂O_ii), which is often used in solution to disinfect surfaces and may besides exist used as a gaseous amanuensis. Hydrogen peroxide solutions are inexpensive skin antiseptics that intermission downwards into water and oxygen gas, both of which are environmentally safety. This decomposition is accelerated in the presence of light, and then hydrogen peroxide solutions typically are sold in brownish or opaque bottles. I disadvantage of using hydrogen peroxide as an antiseptic is that it also causes damage to peel that may delay healing or atomic number 82 to scarring. Contact lens cleaners often include hydrogen peroxide as a disinfectant.

Hydrogen peroxide works past producing gratis radicals that impairment 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, leaner that produce the oxygen-detoxifying enzymes catalase or peroxidase may have inherent tolerance to low hydrogen peroxide concentrations. To kill endospores, the length of exposure or concentration of solutions of hydrogen peroxide must exist increased. Gaseous hydrogen peroxide has greater efficacy and can be used as a sterilant for rooms or equipment.

Figure 12. Catalase enzymatically converts highly reactive hydrogen peroxide (H₂O_ii) into water and oxygen. Hydrogen peroxide can be used to clean wounds. Hydrogen peroxide is used to sterilize items such as contact lenses. (credit photos: modification of work by Kerry Ceszyk)

Plasma, a hot, ionized gas, described as the quaternary state of matter, is useful for sterilizing equipment because it penetrates surfaces and kills vegetative cells and endospores. Hydrogen peroxide and peracetic acid, another unremarkably used peroxygen, each may exist introduced as a plasma. Peracetic acid can be used equally a liquid or plasma sterilant insofar as it readily kills endospores, is more than constructive than hydrogen peroxide even at rather low concentrations, and is immune to inactivation by catalases and peroxidases. It as well breaks down to environmentally innocuous compounds; in this case, acerb acid and oxygen.

Other examples of peroxygens include benzoyl peroxide and carbamide peroxide. Benzoyl peroxide is a peroxygen that used in acne medication solutions. It kills the bacterium Propionibacterium acnes , which is associated with acne. Carbamide peroxide, an ingredient used in toothpaste, is a peroxygen that combats oral biofilms that cause tooth discoloration and halitosis (bad jiff).^[fifteen] Last, ozone gas is a peroxygen with disinfectant qualities and is used to clean air or water supplies. Overall, peroxygens are highly effective and commonly used, with no associated environmental hazard.

Call back Most Information technology

• How do peroxides impale cells?

Supercritical Fluids

Within the last 15 years, the utilise of supercritical fluids, especially supercritical carbon dioxide (scCO₂), has gained popularity for certain sterilizing applications. When carbon dioxide is brought to approximately 10 times atmospheric force per unit area, it reaches a supercritical state that has concrete backdrop between those of liquids and gases. Materials put into a chamber in which carbon dioxide is pressurized in this way can be sterilized because of the power of scCO_two to penetrate surfaces.

Supercritical carbon dioxide works by penetrating cells and forming carbonic acid, thereby lowering the prison cell pH considerably. This technique is effective against vegetative cells and is also used in combination with peracetic acrid to kill endospores. Its efficacy can also be augmented with increased temperature or by rapid cycles of pressurization and depressurization, which more probable produce cell lysis.

Benefits of scCO_two include the nonreactive, nontoxic, and nonflammable backdrop of carbon dioxide, and this protocol is effective at low temperatures. Different other methods, such as estrus and irradiation, that tin can degrade the object being sterilized, the use of scCO_two preserves the object'south integrity and is unremarkably used for treating foods (including spices and juices) and medical devices such as endoscopes. It is also gaining popularity for disinfecting tissues such as skin, bones, tendons, and ligaments prior to transplantation. scCO_two tin can also exist used for pest control considering it tin can kill insect eggs and larvae within products.

Think About It

• Why is the utilise of supercritical carbon dioxide gaining popularity for commercial and medical uses?

Chemical Food Preservatives

Chemical preservatives are used to inhibit microbial growth and minimize spoilage in some foods. Commonly used chemic preservatives include sorbic acid, benzoic acrid, and propionic acid, and their more than soluble salts potassium sorbate, sodium benzoate, and calcium propionate, all of which are used to control the growth of molds in acidic foods. Each of these preservatives is nontoxic and readily metabolized past humans. They are likewise flavorless, so they do non compromise the flavor of the foods they preserve.

Sorbic and benzoic acids exhibit increased efficacy as the pH decreases. Sorbic acrid is thought to work past inhibiting various cellular enzymes, including those in the citric acid cycle, as well as catalases and peroxidases. Information technology is added every bit a preservative in a wide variety of foods, including dairy, staff of life, fruit, and vegetable products. Benzoic acid is found naturally in many types of fruits and berries, spices, and fermented products. It is thought to work by decreasing intracellular pH, interfering with mechanisms such as oxidative phosphorylation and the uptake of molecules such equally amino acids into cells. Foods preserved with benzoic acid or sodium benzoate include fruit juices, jams, ice creams, pastries, soft drinks, chewing gum, and pickles.

Propionic acid is idea to both inhibit enzymes and decrease intracellular pH, working similarly to benzoic acrid. However, propionic acid is a more effective preservative at a higher pH than either sorbic acid or benzoic acid. Propionic acrid is naturally produced by some cheeses during their ripening and is added to other types of cheese and baked appurtenances to prevent mold contamination. It is too added to raw dough to prevent contagion by the bacterium Bacillus mesentericus , which causes bread to become ropy.

Other commonly used chemic preservatives include sulfur dioxide and nitrites. Sulfur dioxide prevents browning of foods and is used for the preservation of dried fruits; information technology has been used in winemaking since aboriginal times. Sulfur dioxide gas dissolves in water readily, forming sulfites. Although sulfites tin be metabolized by the trunk, some people take sulfite allergies, including asthmatic reactions. Additionally, sulfites dethrone thiamine, an important nutrient in some foods. The manner of action of sulfites is not entirely clear, but they may interfere with the disulfide bond formation in proteins, inhibiting enzymatic activeness. Alternatively, they may reduce the intracellular pH of the jail cell, interfering with proton motive force-driven mechanisms.

Nitrites are added to candy meats to maintain color and cease the germination of Clostridium botulinum endospores. Nitrites are reduced to nitric oxide, which reacts with heme groups and iron-sulfur groups. When nitric oxide reacts with the heme group inside the myoglobin of meats, a red product forms, giving meat its red colour. Alternatively, it is idea that when nitric acid reacts with the iron-sulfur enzyme ferredoxin within bacteria, this electron transport-chain carrier is destroyed, preventing ATP synthesis. Nitrosamines, nonetheless, are carcinogenic and can be produced through exposure of nitrite-preserved meats (due east.g., hot dogs, tiffin meat, breakfast sausage, bacon, meat in canned soups) to heat during cooking.

Natural Chemic Food Preservatives

The discovery of natural antimicrobial substances produced past other microbes has added to the arsenal of preservatives used in food. Nisin is an antimicrobial peptide produced by the bacterium Lactococcus lactis and is particularly effective against gram-positive organisms. Nisin works by disrupting jail cell wall production, leaving cells more than decumbent to lysis. It is used to preserve cheeses, meats, and beverages.

Natamycin is an antifungal macrolide antibiotic produced by the bacterium Streptomyces natalensis . Information technology was approved by the FDA in 1982 and is used to preclude fungal growth in diverse types of dairy products, including cottage cheese, sliced cheese, and shredded cheese. Natamycin is also used for meat preservation in countries outside the United states of america.

Think About It

• What are the advantages and drawbacks of using sulfites and nitrites as food preservatives?

Key Concepts and Summary

• Heavy metals, including mercury, silver, copper, and zinc, have long been used for disinfection and preservation, although some have toxicity and environmental risks associated with them.
• Halogens, including chlorine, fluorine, and iodine, are besides commonly used for disinfection. Chlorine compounds, including sodium hypochlorite, chloramines, and chlorine dioxide, are unremarkably used for water disinfection. Iodine, in both tincture and iodophor forms, is an effective clarified.
• Alcohols, including ethyl alcohol and isopropyl alcohol, are commonly used antiseptics that human action past denaturing proteins and disrupting membranes.
• Phenolics are stable, long-acting disinfectants that denature proteins and disrupt membranes. They are ordinarily establish in household cleaners, mouthwashes, and hospital disinfectants, and are also used to preserve harvested crops.
• The phenolic compound triclosan, found in antibacterial soaps, plastics, and textiles is technically an antibody because of its specific fashion of activeness of inhibiting bacterial fatty-acid synthesis..
• Surfactants, including soaps and detergents, lower the surface tension of water to create emulsions that mechanically carry away microbes. Soaps are long-chain fatty acids, whereas detergents are constructed surfactants.
• Quaternary ammonium compounds (quats) are cationic detergents that disrupt membranes. They are used in household cleaners, peel disinfectants, oral rinses, and mouthwashes.
• Bisbiguanides disrupt jail cell membranes, causing jail cell contents to gel. Chlorhexidine and alexidine are commonly used for surgical scrubs, for handwashing in clinical settings, and in prescription oral rinses.
• Alkylating agents finer sterilize materials at low temperatures but are carcinogenic and may also irritate tissue. Glutaraldehyde and o-phthalaldehyde are used every bit hospital disinfectants simply non as antiseptics. Formaldehyde is used for the storage of tissue specimens, as an embalming fluid, and in vaccine preparation to inactivate infectious agents. Ethylene oxide is a gas sterilant that can permeate heat-sensitive packaged materials, simply it is also explosive and carcinogenic.
• Peroxygens, including hydrogen peroxide, peracetic acid, benzoyl peroxide, and ozone gas, are stiff oxidizing agents that produce gratuitous radicals in cells, damaging their macromolecules. They are environmentally condom and are highly effective disinfectants and antiseptics.
• Pressurized carbon dioxide in the grade of a supercritical fluid easily permeates packaged materials and cells, forming carbonic acid and lowering intracellular pH. Supercritical carbon dioxide is nonreactive, nontoxic, nonflammable, and effective at low temperatures for sterilization of medical devices, implants, and transplanted tissues.
• Chemical preservatives are added to a variety of foods. Sorbic acid, benzoic acid, propionic acrid, and their more soluble salts inhibit enzymes or reduce intracellular pH.
• Sulfites are used in winemaking and food processing to prevent browning of foods.
• Nitrites are used to preserve meats and maintain color, just cooking nitrite-preserved meats may produce carcinogenic nitrosamines.
• Nisin and natamycin are naturally produced preservatives used in cheeses and meats. Nisin is effective against gram-positive leaner and natamycin against fungi.

Multiple Choice

Which of the following refers to a disinfecting chemical dissolved in alcohol?

1. iodophor
2. tincture
3. phenolic
4. peroxygen

Show Answer

b. Tincture refers to a disinfecting chemical dissolved in alcohol.

Which of the following peroxygens is widely used as a household disinfectant, is cheap, and breaks down into water and oxygen gas?

1. hydrogen peroxide
2. peracetic acid
3. benzoyl peroxide
4. ozone

Show Answer

a. Hydrogen peroxide is widely used as a household disinfectant, is inexpensive, and breaks downwards into h2o and oxygen gas.

Which of the post-obit chemical nutrient preservatives is used in the wine industry but may cause asthmatic reactions in some individuals?

1. nitrites
2. sulfites
3. propionic acid
4. benzoic acrid

Prove Answer

b. Sulfites are used in the wine industry merely may crusade asthmatic reactions in some individuals.

Bleach is an example of which group of chemicals used for disinfection?

1. heavy metals
2. halogens
3. quats
4. bisbiguanides

Show Answer

b. Bleach is an example of halogens.

Which chemical disinfectant works by methylating enzymes and nucleic acids and is known for beingness toxic and carcinogenic?

1. sorbic acid
2. triclosan
3. formaldehyde
4. hexaclorophene

Show Reply

c. Formaldehyde works past methylating enzymes and nucleic acids and is known for beingness toxic and carcinogenic.

Fill up in the Blank

Doorknobs and other surfaces in clinical settings are frequently coated with ________, ________, or ________ to prevent the transmission of microbes.

Evidence Answer

Doorknobs and other surfaces in clinical settings are often coated with copper, nickel, and zinc to prevent the transmission of microbes.

True/Fake

Soaps are classified as disinfectants.

Mercury-based compounds take fallen out of favor for use every bit preservatives and antiseptics.

Think Virtually Information technology

1. Which solution of ethyl alcohol is more effective at inhibiting microbial growth: a 70% solution or a 100% solution? Why?
2. When might a gas treatment exist used to control microbial growth instead of autoclaving? What are some examples?
3. What is the advantage of using an iodophor rather than iodine or an iodine tincture?
4. Looking at Figure 11, which alkylating amanuensis shown lacks an aldehyde group?
5. Practice you lot think naturally produced antimicrobial products like nisin and natamycin should replace sorbic acrid for food preservation? Why or why non?
6. Why is the utilize of skin disinfecting compounds required for surgical scrubbing and non for everyday handwashing?

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Source: https://courses.lumenlearning.com/microbiology/chapter/using-chemicals-to-control-microorganisms/

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