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One of the most common disinfection methods is the chemical method. In this case, chemical substances are used - disinfectants (disinfectants, disinfectants).
Chemicals that kill bacteria are called bactericidal (from Latin caedo - I kill), and substances that inhibit their vital activity are called bacteriostatic. The concentration of compounds that cause bacteriostatic action is much less bactericidal. Spore-killing chemicals are called sporicides, viruses that kill viruses are called virucides, and fungi-kills are called fungicides.
Various factors influence the antimicrobial activity of disinfectants:
1. The range of antimicrobial activity. Disinfectants should have a wide range of activity. Among bacteria, gram-positive, such as staphylococci, are most easily destroyed, while gram-negative are more resistant to disinfectants.
2. The number of bacteria. The behavior of disinfectants is influenced not only by the type of bacteria, but also by their number. One cannot say about any disinfectant with certainty that it will cause the death of 100% of the germs. The destruction of 99.9% of bacteria is recognized as adequate and is a guarantee of safety. However, a simple calculation shows that with 99.9% of bacteria killed, 100 out of every million survive. It should be borne in mind that under favorable conditions, one bacterium can multiply and reproduce about 1,000,000,000 cells within 10 hours.
3. Reach bacteria. Disinfectants to neutralize bacteria must come in direct contact with microorganisms. Before using them, remove organic substances from surfaces to ensure access to bacteria. In addition, cleaning removes most bacteria, and the remaining ones become more accessible to disinfectants. Therefore, a two-stage process gives the best effect - first preliminary cleaning of the surfaces, and then the use of disinfectant solutions.
4. Temperature. All disinfectants are most effective at high temperatures, so it is best to use them in hot water.
5. Concentration. Disinfectants should be used in certain concentrations. If the concentration is lower than recommended, then there is no point in using such disinfectants.
6. Volume. At the same concentration, the effectiveness of a larger disinfectant is higher than less.
7. pH of the medium. The action of drugs is mainly stronger in an acidic environment than in an alkaline one. Some disinfectants are sensitive to changes in pH, so the addition of an alkaline “activator” is necessary for some of them.
8. Time. There is no instant disinfection. To perform their work, all disinfectants require a certain time, which depends on the type, temperature, concentration and volume of the disinfectant, as well as the nature of the bacteria present, the amount and type of material. At lower temperatures and concentrations, with difficult access to bacteria, more time is required to achieve efficacy. The result of disinfection depends on the resistance of microbes: first, less stable vegetative forms of microorganisms die, and then more resistant - spore forms. Under the same conditions, gram-negative bacteria die more slowly than gram-positive ones. Acid-resistant bacteria slow down more slowly. The activity of most disinfectants ceases after they dry.
The fastest disinfectants are chlorine and alcohol - their disinfecting effect appears after 2 minutes (provided that the surface is clean).
9. Decrease in activity. After dilution with water, the effectiveness of many disinfectants gradually decreases. Being effective fresh, they can become ineffective over the following days. This situation is dangerous and can become a source of infection, because the bacteria that survived in the disinfectant solution can multiply in it. The danger of bacterial growth in disinfectant solutions should be recognized. The longer the storage or use of the disinfectant, the higher its concentration.
10. Inactivation. All chemical disinfectants are inactivated under certain conditions. Hard water, organic materials (including food, including milk), artificial materials (nylon, polyurethane, polyethylene, polypropylene, styrene, polyvinyl chloride and polyvinyl acetate) reduce the activity of some disinfectants. Acidic detergents inactivate alkaline disinfectants such as phenols or chlorine compounds. One disinfectant can inactivate another. Do not use two disinfectants or one immediately after the other.
Hygienic disinfectants should:
• have a wide antimicrobial spectrum of action;
• have low toxicity and allergenicity to humans;
• have good solubility in water or easily form suspensions, emulsions in it;
• act in the lowest possible concentrations and kill microorganisms as soon as possible;
• keep active in a disinfected environment;
• be sufficiently resistant during storage;
• do not damage the treated surfaces;
• be affordable, cheap and easy to transport, during storage and use.
The best medium for contact with a microbial cell is water, therefore, drugs that are readily soluble in water are used as disinfectants. The presence of lumps of disinfectant in the solution or at the bottom leads to a decrease in the estimated concentration of working solutions.
When a disinfectant acts on a microbial cell, the disinfectant must first enter the cell, and then the reaction between the active substance and the constituent parts of the cell.
According to the mechanism of action on a microbial cell, chemical disinfectants are divided into: coagulating protein (phenol, cresol and their derivatives, alcohols, salts of heavy metals); causing swelling and dissolution of the protein (caustic alkali, quaternary ammonium compounds, hydrated lime); oxidizing agents (chlorine, bromine and iodine compounds, potassium permanganate, hydrogen peroxide); other disinfectants (sodium metasilicate, formalin, etc.).
Only disinfectants that have passed sanitary and epidemiological examination in accordance with the order of the Ministry of Health of the Russian Federation “On Sanitary and Epidemiological Expertise of Products” dated August 15, 01, No. 325 and state registration in accordance with the Decree of the State Committee for Epidemiological Inspection of the Russian Federation “Regulation on State registration and state control of the quality of disinfectants in the Russian Federation ”dated 11.11.94 No. 11. Imported disinfectants must be authorized and meet the requirements of sanitary rules, de acting per the Russian Federation.
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