Chapter 9 Antisepsis and Disinfection What is an antiseptic? An antiseptic is a substance that Destroys or inhibits the growth of microorganisms 1,2 Is suitable for application on living tissues Define antisepsis. Antisepsis is defined as the process of destruction or inhibition of microorganisms in or on living tissue. 3 What is a disinfectant? A disinfectant is a substance That destroys harmful microbes That is applicable to inanimate objects Where spores are usually not destroyed What do you understand by disinfection? Disinfection involves killing of infectious agents outside the body by exposure to either chemical or physical agents. Hence, disinfection is reduction in the load of pathogens. What do you understand by sterilization and how is it different from disinfection? Sterilization is the process used to render a product free from viable organisms including bacterial spores. Hence, it is the procedure of destroying all life including spores. Disinfection, on the other hand, removes only the pathogens or leads only to a reduction in the bioload of disease-causing organisms. What is a deodorant? A deodorant is a substance that suppresses or neutralizes bad odors, e.g., lime and bleaching powder. What is a detergent? A detergent is a substance that acts as a surface cleaning agent. It does so by lowering the surface tension thereby emulsifying oils and hold dirt in suspension. This suspension is washed away with water, e.g., soap. Soap removes dirt, and bacteria are removed along with it. SOAP Figure 9.1 A bar of soap is displayed in Figure 9.1.
Antisepsis and Disinfection 123 For what purpose is it used? It is used for detergent purposes; it is a surface acting agent. How does it act? It acts by lowering the surface tension and emulsifying the dirt and holding it in suspension. What are its uses? For cleaning the skin For hand washing Soap water is used for cleaning dog bite wounds and for enema CRUDE PHENOL Figure 9.2 The spot displayed in Figure 9.2 is crude phenol. What is its chemical name? Pure phenol is carbolic acid Crude phenol, which is the commonly used form, is a mixture of phenol (carbolic acid) and cresol How do you disinfect cholera stool? Cholera stool is disinfected by putting an equal amount of 10% crude phenol (or 10% formalin) over it and then allowing the disinfectant to act for 1 2 hours. What is chemical cautery and what is its drawback? Using carbolic acid (phenol) or any other chemical to cauterize a skin wart, unhealthy granulation, etc., is called chemical cautery. Its main drawback is that it is difficult to precisely control the amount of chemical applied on the lesion. 1,2 What is Rideal Walker coefficient? The Rideal Walker coefficient is a method of determining the relative germicidal values of different disinfectants. Carbolic acid is the standard to which the disinfecting power of various germicides is referred. Salmonella typhi is used as the test organism. An RWC of 10 means the disinfection is 10 times more powerful than carbolic acid. 2,4 What is the composition of crude phenol? Crude phenol = cresol + phenol Against which organisms are they effective? They are effective against gram-positive and gram-negative organisms. What concentration do you use for disinfecting feces? 10% strength
124 Mastering Practicals: Community Medicine DETTOL Figure 9.3 The spot displayed in Figure 9.3 is dettol. To which group does it belong? Phenol-related compounds What is its chemical name? Chloroxylenol Why is it used in the hospital? It is used for disinfecting Instruments Plastic equipment In what strength is it used for disinfecting instruments and plastic equipment in the hospital? 5% Dettol is suitable for the purpose of disinfecting instruments and plastic equipment. What is the minimum contact period? 15 minutes How do you disinfect a clinical thermometer before use? A clinical thermometer is disinfected by dipping it in a solution of one part of Savlon and six parts of spirit for 3 minutes. LIME (SLAKED LIME) Figure 9.4 Slaked lime is displayed in Figure 9.4.
Antisepsis and Disinfection 125 What is its use? It is used as a disinfectant and deodorant. What is its aqueous solution known as? Milk of lime it is 10 20% aqueous suspension of lime. How do you disinfect cholera stool in the rural areas by using this? Cholera stool in the rural areas is disinfected by mixing two volumes of milk of lime and one volume of feces and allowing it to stand for 2 hours. What are its other uses? It is also used for whitewashing since this is effective in disinfecting walls. BLEACHING POWDER Figure 9.5 A bottle of bleaching powder is displayed in Figure 9.5. What are its uses? It is used For disinfecting water, feces, and urine As a deodorant What is its mechanism of action? It disinfects by emitting chlorine. What are the advantages of using this as a disinfectant? Relatively cheap Disinfection is rapid What are the drawbacks of using this as a disinfectant? It is an unstable compound and loses its chlorine content on storage. Its action is brief. What is the recommended level of residual chlorine? 0.5 mg per liter for 1 hour How will you test for residual chlorine? Orthotolidine arsenite test. The steps are listed in the chapter on environment (Chapter 8).
126 Mastering Practicals: Community Medicine Which type of disinfection is chlorination of drinking water? Precurrent or prophylactic disinfection. This means that the disinfection is done as a preventive measure. This is in contrast to concurrent disinfection which is done while a person is ill. Another example of precurrent disinfection is pasteurization of milk. POVIDONE IODINE Figure 9.6 The spot displayed in Figure 9.6 is a solution of povidone iodine. Which group does it belong to? Iodophor Where is it commonly used? It is commonly used as a skin antiseptic before surgery and on wounds. What is the advantage of using halogens as disinfective agents? Halogens are actively bactericidal. They are the only usable antiseptics with a sporicidal action. What are its advantages over the alcoholic solution of iodine? It does not irritate the skin unlike the iodine solution. It does not stain the skin whereas iodine solution does. ETHYL ALCOHOL Figure 9.7 The spot displayed in Figure 9.7 is ethyl alcohol.
Antisepsis and Disinfection 127 In what concentration is it most effective? 70% strength Is it effective against spores? No What are its drawbacks? It has no action against spores. It is inflammable, hence used only for small articles. Its activity disappears as soon as the alcohol dries off. SAVLON Figure 9.8 The spot displayed in Figure 9.8 is savlon. What is the combination? Cetavlon + hibitane To which group does it belong? Quaternary ammonia compounds What is its common use? It is used for disinfecting Plastic appliances such as Lippes loop Clinical thermometer What is the minimum contact period while using Savlon one part in six parts of spirit? The minimum contact period for Lippes loop is 20 minutes and for thermometer 3 minutes.
128 Mastering Practicals: Community Medicine FORMALIN Figure 9.9 The spot displayed in Figure 9.9 is formalin. To which group does it belong? Formaldehyde What is the strength of solution recommended for disinfecting a room? 2 3% concentration For what purpose is it used? It is used for disinfecting and preserving organs. What are its advantages over others? It can destroy all microorganisms including spores and acid fast bacilli (though slowly). How will you disinfect rooms, walls, and furniture? A combination of 20 30 ml of 40% formalin in 1 L of water is used for spraying rooms, walls, and furniture. Name some articles which are suitable for disinfection with formaldehyde gas. Blankets Beds Books Other valuable items which cannot be boiled 1,2 References 1. Park K. Principles of epidemiology and epidemiologic methods. In: Park s Textbook of Preventive and Social Medicine, 20th ed. Jabalpur, India: M/S Banarasidas Bhanot Publishers; 2009. 2. Vaidya R, Bhatti VK. General prevention and control measures. In: Vaidya R, Tilak R, Gupta R, Kunte R, editors. Text Book of Public Health and Community Medicine, 1st ed. Pune: Dept. Community Medicine, AFMC, in collaboration with WHO, India office, Delhi; 2009:1001 1008. 3. McDonnell GE. Antisepsis, Disinfection, and Sterilization: Types, Action, and Resistance. Washington, DC: American Society for Microbiology Press; 2007: 378. 4. Kendall AI, Edwards MR. A method for determining the germicidal value and penetrating power of liquid disinfectants. J Infect Dis 1911;8(2): 250 7.