Prof. Khan Chapter7
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| Antimicrobial Agent: | substances that kill microbes or prevent their growth. (antibacterial, antifungal, antiviral)
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| Microbicidal: | antimicrobial agents that kill microorganisms. (bactericidal, fungicidal, virucidal)
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| Microbistatic | Antimicrobial agent that inhibit(stops) the growth of microbes.
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| Sterilization: | the process of destroying or removing all forms of microbial life.
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| Disinfection: | : a process (physical or chemical) that kills the vegetative forms of microbes, but does not necessarily kill their spores. A disinfectant (germicidal) is a substance used on inanimate objects.
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| Antisepsis: | a process which applies antiseptic to the surface of the body (skin and mucous membrane) to kill or inhibit the growth of microbes.
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| Sanitization | a process which reduces microbial population to levels that are considered safe by public health guidelines.
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| Factors that Influence the Action of Antimicrobial Agents | 1. The number of microorganisms. 2.The nature of microbe. 3.The temperature and pH of the environment.4.The concentration the agent.5. The physiological state of the cell.
6. Presence of interfering (extraneous) organic matter.
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| What is Microbial Death? | Inability to reproduce under optimum growth conditions.
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| Mode of Action of Antimicrobial Agents | 1.Damage to cell wall 2.Alteration of cell membrane 3.Damage to proteins and nucleic acids
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| 1.Damage to cell wall | Examples: lysozyme, lysostaphin, penicillins.
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| 2.Alteration of cell membrane | Examples: polymixin-b, cepacol
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| 3.Damage to proteins and nucleic acids | Examples: radiations, alcohols, acids, and chloramphenicol.
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| Methods of Physical Control | 1. Hight temperature 2. Low temperature ( microbistatic)3.Desiccation(microbisatic)4. Radiation 5. Filtration
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| I. High Temperature - Moist Heat | is 1of the most effectove and utilized means of killing microbes.It causes denaturation of vital proteins such as enzymes. Endospores of B. Anthracis are destroyed by moist heat within 2-15 min.at 100ºC,while dry heat takes 180 minutes at 140 C.
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| Types of moist heat | 1. steam under pressure ( autoclave) 2. Boiling water ( disinfection)
3. Subboiling temperatures (pasteurization):
4. Tyndallization (fractional sterilization):
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| Steam under pressure (autoclave) | it is the most practical and dependable way to destroy vegetative forms and their endospores. It is usually operated at a pressure of 15lb per square inch (psi)at 121ºC. The st. time varies from 10 minutes for light loads to 40 min. for heavy loads-av.20m
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| Boiling water (disinfection): | ): Water brought to boiling point (100ºC) will kill vegetative microbes only. Endospores of some bacteria can survive boiling fro several hours.
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| . Subboiling temperatures (pasteurization): | 1. LTH (Low Temperature Holding)
62-66ºC for 30 minutes
2. HTST (High Temperature Short Time)
72º C for 15 seconds
Why Don’t We Sterilize Milk?
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| Tyndallization (fractional sterilization): | Heat-Labile material is heated to 80-100ºC for 30-60 minutes on each of three successive days with incubation periods in between.
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| Dry Heat - Hot-Air-Oven: | is used to sterilize substances impermeable to or damaged by moisture such as oils, powders etc.
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| Dry Heat - Incineration | destruction of microbes by burning.
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| Low Temperatures (microbistatic) | Freezing is used to preserve food,drugs,lab specimen etc.It may not kill the microorganisms and may in fact preserve them along with the material being frozen.
Frozen culture can be stored indefinit. at -70ºC or in tanks of liquid nitrogen at -196ºC.
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| Desiccation (microbistatic) | Drying vegetative cells of microbes inhibits their metabolic activities.
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| The length of time microbes survive after desiccation depends on the following factors: | 1. The type of the microorganism
2. The material in or on which the organisms are dried.
3. The completeness of the drying process.
4. The physical conditions involved, such as temperature and humidity.
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| Neisseria Gonarrhoeae and Neisseria Meningitidis | are extremely sensitive to desiccation and die within few hours after being dried.
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| Mycobacterium Tuberculosis | can survive in dried sputum for several months.
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| Endospores of bacillus and clostridium | can survive thousands of years without water.
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| IV. Radiation: | It is classified according to its wavelength. The energy content of the radiation is inversely related to its wavelength: the shorter the wavelength, the greater the energy content.
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| Ionnizing Radiations (cold sterilization): | ): destroy DNA and cause ionization of molecules, they drive away electrons and split the molecules into atoms or groups of atoms.
Examples: gamma rays and x-rays
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| Nonionizing Radiations: | UV light excites its electrons,causing the molecules to react differently. UV light causes the formation of thyminedimmers in the DNA. Because of its low energy content the object to be disinfected must be directly exposed to UV light for full effect.
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| V. Filtration: | It is used to sterilize materials (serum, vaccines, IV fluids, enzymes, media) that cannot be sterilized by autoclaving.
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| Membrane Filters: | are used to remove microbes from liquids.
Pore size varies from 0.01 um (for viruses) to 0.22 um (for bacteria).
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| High-Efficiency Particulate Air (HEPA) Filters: | : remove 99% of the particulate matter from the existing air. Used in Lab procedures that involve working with potentially hazardous materials, such as diseased animal tissues, infectious microbes, genetically engineered microbes.
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| Chemical Agents of Microbial Control Characteristics of an Ideal Chemical Agent | 1.Antimicrobial Activity 2. Solubility: 3. Lack of Toxicity 4. Stability: 5. Minimum Inactivation by Extraneous Material: 6. Availability: 7. Material Safety:
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| 1.Antimicrobial Activity | : the chemical, at low concentration, should have a broad spectrum of antimicrobial activity.
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| 2. Solubility: | the compound should be soluble in water or other suitable solvents (such as alcohol) for ease of preparation and application.
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| 3. Lack of Toxicity | it should not harm human or other animals.
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| 4. Stability: | changes in the substance upon standing should be minimal and should not result in significant loss of germicidal action
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| 5. Minimum Inactivation by Extraneous Material: | many disinfectants have an affinity for proteins and other organic compounds found in the material being treated. This decreases the amount of chemical available for action against microorganisms
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| 6. Availability: | the product should be readily available and inexpensive
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| 7. Material Safety: | the compound should not rust or disfigure metals, nor should it stain or damage fabric.
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| Major Groups of chemical Anti-Microbial Agents | 1. Phenol and Phenolic Derivatives:
2. Chlorhexidine (hibiclens, hibitane):
3. Alcohols
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| 1. Phenol and Phenolic Derivatives: | A. Phenol (carbolic acid) was used by Lister during 1860s in his work to develop aseptic surgical techniques.
B. Phenol is also the standard compound with which other disinfectants are compared.
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| 1. Phenol and Phenolic Derivatives: | Phenol is quite caustic to human tissue and has an unpleasant odor, so it has been replaced by other phenolic derivatives such as Lysol(o-phenyl-phenol)&clearsol(0-cresol.D.Use of hexahlorophene has been stop -1972 b.of this damaging effect on nervos sys.
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| 1. Phenol and Phenolic Derivatives: | E. Phenolic derivatives in low concentration (1%or lower) are widely used as antiseptics and in higher concentration (2%or higher)as disinfectants.
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| 1. Phenol and Phenolic Derivatives: | F.High concentration of phenols function by denaturing and disruption cell membranes and cell walls, while at lower concentration they inactivate enzymes.
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| 1. Phenol and Phenolic Derivatives: | G. Phenolics may be microbistatic or microbicidal depending on the concentration but are not reliable sporicidal agents.
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| 2. Chlorhexidine (hibiclens, hibitane): | A. Commonly used to disinfect skin and mucous membrane.
B. It is non-toxic, non-irritant, and non-absorbable by the skin.
C. It is microbicidal (disrupt cell membrane) but not sporicidal.
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| 3. Alcohols | A. Microbicidal but not sporicidal.
B. Most effective when applied as 50 to 70 percent aqueous solution.
C. Commonly used as antiseptics on human skin both individually and in combination with a halogen like iodine.
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| 3. Alcohols | D. Alcohols precipitate proteins and solubilize lipids present in the cell walls and membranes of bacteria.
4. Halogens (Iodine, Chlorine, Fluorine and Bromine):
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| Iodine and Iodine Compounds | A. Iodine is slightly soluble in water but readily soluble in alcohol and aqueous solutions of potassium or sodium iodide.
B. Iodine has both germicidal and antiseptic effect when dissolved in 70% alcohol (tincture of iodine).
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| Iodine and Iodine Compounds | C. Idophores (complex of iodine and organic carrier: betadine, povidone, and isodine) are nonstaining and slowly release iodine at the site of application.
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| Iodine and Iodine Compounds | D. The exact mode of action of iodine is not clearly understood. It has been suggested that it inactivated proteins and organic molecules by halogenation of tyrosine (a common amino acid of many enzymes and other cellular proteins).
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| Chlorine and Chlorine Compounds | A. Chlorine Gas is used to disinfectant community water supplies.
B. Hypochlorites are commonly used to sanitize and disinfect food equipment in dairy, spas, swimming pools etc.
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| Chlorine and Chlorine Compounds | C. Chloramines (dichloramine, halazone) are more stable than other forms of chlorine and do not produce trihalomethanes (cancer causing substance).
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| Chlorine and Chlorine Compounds | D. Chlorine and its compounds destroy cells by forming hypochlorous acid and nacent oxygen which is a very strong oxidizing agent.
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| Gaseous Chemosterilizers | A. Ethylene oxide gas is commonly used to due to its strong penetrating power.
B. Due to its carcinogenic and explosive nature, it is combined with other gases like carbon dioxide and nitrogen.
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| Gaseous Chemosterilizers | C. Commonly used to sterilize medical supplies such as heart-lung machine, artificial heart valves etc.
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