The fundamentals of disinfection and sterilization
The process of sterilization involves eliminating or destroying all germs, including the extremely resilient bacterial spores. The most common method of sterilization is autoclaving, which involves 15 minutes of exposure to steam at 121°C and 15 lb/in2 of pressure. Most intravenous fluids are sterilized via filtration, and surgical tools that are susceptible to damage from wet heat are often sterilized by exposure to ethylene oxide gas.
Disinfection is the process of killing most germs, but not all of them. Pathogens must be eliminated for proper disinfection, however, certain organisms and bacterial spores might endure. Disinfectants come in a range of tissue-damaging qualities, from phenol-containing chemicals that are corrosive and should only be used on inanimate items to less toxic ingredients like ethanol and iodine that are safe for use on skin surfaces.
Antiseptics are substances that are used to destroy bacteria on the skin's and mucous membranes' surface.
RATE OF MICROORGANISM DEATH
The rate at which microorganisms die is essentially determined by two factors: the concentration of the killing agent and the duration of application. The connection N α 1/CT, which indicates that the number of survivors, N, is inversely proportional to the agent's concentration, C, and the agent's application time, T, defines the killing rate. CT is sometimes referred to as the dose when taken as a whole. Alternatively, there exists a direct correlation between CT and the quantity of germs eliminated. Since colony formation is a simple way to measure survivors, the connection is typically expressed in terms of survivors. The inability to procreate is the definition of death.
Chemical Agents
The effectiveness of chemicals in destroying microbes varies widely. The phenol coefficient, which is the ratio of the phenol concentration to the concentration of the agent needed to produce the same amount of death under the test's usual circumstances, provides a quantifiable assessment of this variation.
One of the three main methods by which chemical agents work is (1) disruption of the cell membrane that contains lipids, (2) modification of proteins, or (3) modification of DNA. The subsequent chemical agents have been categorized into one of the three groups; however, several compounds exhibit multiple mechanisms of action.
DEFECTS IN CELL MEMBRANES
Booze
It is common practice to cleanse the skin with ethanol before venipuncture or vaccination. It primarily works by destabilizing the lipid composition of membranes, however, it also denatures proteins. For ethanol to function at its best, water must be present (that is, ethanol works significantly better at 70% than at 100%). An antiseptic solution containing 70% ethanol is frequently used to cleanse the skin before venipuncture. However, iodine-containing compounds work better than this one, therefore it's best to use them before getting a blood culture and inserting intravenous catheters.
Disinfectants
A polar hydrophilic group, which may be a cation, an anion, or a nonionic group, and a long-chain, lipid-soluble, hydrophobic component makeup detergents, which are classified as "surface-active" agents. Through their hydrophobic chain interaction with the lipid in the cell membrane and their polar group interaction with the surrounding water, these surfactants cause disruptions to the membrane. Catalytic detergents with quaternary ammonium compounds, like benzalkonium chloride, are frequently used to treat skin sepsis. The active component of Lysol, a popular floor and surface disinfectant, is benzalkonium chloride.
Phenols
Lister utilized phenol as the first disinfectant in the operating room in the 1860s, but due to its extreme causticity, it is rarely used nowadays. Chlorhexidine is a chlorinated phenol that is frequently used to clean wounds and disinfect hands before surgery (sometimes known as a "surgical scrub").
In germicidal soaps, hexachlorophene—a biphenol with six chlorine atoms—is employed; however, due to potential neurotoxicity, its application has been restricted. Phenols denature proteins in addition to harming membranes.
ALTERATIONS IN PROTEINS
Chlorine
Chlorine is a disinfectant that is used to cleanse swimming pools and purify water supplies. It is also the active ingredient in hypochlorite, or bleach (Clotro), a disinfectant that is used in hospitals and homes. Strong oxidizers like chlorine kill by cross-linking vital sulfhydryl groups in enzymes to create inert disulfide.
Iodine
The most effective skin antiseptic in medical practice is iodine, which is recommended before taking a blood culture and inserting intravenous catheters due to the potential risk of skin flora contamination, including Staphylococcus epidermidis. Similar to chlorine, iodine is an oxidant that renders enzymes containing sulfur hydroxide inactive. Additionally, it binds selectively to protein tyrosine residues.
The supply of iodine comes in two forms:
(1) Before blood culture, the skin is prepared using a tincture of iodine, a 2% solution of iodine, and potassium iodide in ethanol. Iodine tincture should be removed with alcohol because it can irritate the skin.
(2) Iodophors, which are iodine and detergent complexes, are commonly used to prepare the skin before surgery.
Hefty metals
The two heavy metals that are most frequently employed in medicine are mercury and silver, which also have the strongest antibacterial properties. They work by attaching themselves to sulfhydryl groups and preventing the action of enzymes.
Mercury-containing merbromin (Mercurochrome) and thimerosal (Merthiolate) are used as skin antiseptics. Gonococcal ophthalmia neonatorum can be prevented with the help of silver nitrate drops. Burn wounds are kept from becoming infected by using silver sulfadiazine.
Hydrogen Peroxide
As an antiseptic, hydrogen peroxide is used to treat wounds and sanitize contact lenses. The organism's capacity to generate catalase, an enzyme that breaks down H2O2, limits its efficacy. (The oxygen created when peroxide is applied to wounds is a result of tissue catalase breaking down H2O2). An oxidizing chemical called hydrogen peroxide targets sulfhydryl groups to prevent enzymatic action.
Glutaraldehyde with Formaldehyde
Formaldehyde denatures proteins and nucleic acids. It is sold as formalin, a 37% aqueous solution. Essential -NH2 and -OH groups are found in both proteins and nucleic acids, and they serve as the primary locations where the formaldehyde hydroxymethyl group alkylates molecules. With two reactive aldehyde groups, glutaraldehyde is less hazardous and ten times more potent than formaldehyde. It is used to sterilize hemodialysis equipment, endoscopes, and respiratory treatment equipment in hospitals.
Oxygenated Ethylene
Hospitals frequently employ ethylene oxide gas to sterilize heat-sensitive items like plastics and surgical tools. It kills by alkylating proteins and nucleic acids, attacking the reactive hydrogen atoms on crucial amino and hydroxyl groups with the hydroxyethyl group.
Alkalis and Acids
Proteins are rendered denaturable by strong acids and alkalis. Mycobacterium TB and other mycobacteria are relatively resistant to 2% NaOH, which is employed in clinical laboratories to liquefy sputum before culture the organism, even though most bacteria are sensitive. Because they are bacteriostatic, weak acids like citric, propionic, and benzoic acids are commonly employed as food preservatives.
CHANGES IN NUCLEIC ACIDS
Different dyes have the dual properties of staining bacteria and preventing their development. Among these is crystal violet, often known as gentian violet, which is applied topically as an antibacterial. The positively charged dye molecule binds to the negatively charged phosphate groups of the nucleic acids, which is how it works. Malachite green, a crystal violet that resembles a triphenylamine dye, is a part of Löwenstein-Jensen's medium, which is used to cultivate M. tuberculosis. The 6-week incubation time of the dye prevents undesirable germs from growing in the sputum.
ACTUAL AGENTS
The physical agents work by either filtering out microorganisms or transferring energy in the form of heat or radiation.
HEAT
There are three ways to apply heat energy: through pasteurization, dry heat, or moist heat (such as boiling or autoclaving). Heat generally kills via denaturing proteins, but it can also do so by rupturing membranes and cleaving DNA enzymatically. Because water helps break noncovalent interactions (like hydrogen bonds), which link protein chains together in their secondary and tertiary structures, moist heat sterilizes at a lower temperature than dry heat.
The most common type of sterilization is moist heat, which is typically autoclaving.
Bacterial spores need to be exposed to a greater temperature because they cannot withstand boiling, which is 100°C at sea level. This is accomplished by using an autoclave chamber, where steam is forced to achieve 121°C at a pressure of 15 lb/in 2 and is maintained there for 15 to 20 minutes. With a margin of safety, this destroys even the extremely heat-resistant spores of Clostridium botulinum, the source of botulism. Spore-forming microbes, such as those in the genus Clostridium, are used to evaluate the efficiency of the autoclaving process.
Pasteurization is the process of heating milk to 62°C for 30 minutes and then quickly cooling it down. It is mostly used for milk. ("Flash") pasteurization is frequently performed for 15 seconds at 72°C. This is insufficient to sterilize the milk; rather, it only kills the pathogens' vegetative cells, such as Salmonella, Listeria, Brucella, Mycobacterium bovis, and Streptococcus.
