Chapter 7 - Control of microbial growth

Chapter 7 - Control of microbial growth - Chapter 7(Tortora...

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Chapter 7 (Tortora) Control of Microbial Growth The Control of Microbial Growth PHYSICAL AND CHEMICAL CONTROL OF MICROBES 1. Antimicrobial Agent: substances that kill microbes or prevent their growth. (antibacterial, antifungal, antiviral) 2. Microbicidal: antimicrobial agents that kill microorganisms. (bactericidal, fungicidal, virucidal) 3. Microbistatic: Antimicrobial agent that inhibit the growth of microbes. 4. Sterilization: the process of destroying or removing all forms of microbial life. 5. 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. 6. Antisepsis: a process which applies antiseptic to the surface of the body (skin and mucous membrane) to kill or inhibit the growth of microbes. 7. Sanitization: a process which reduces microbial population to levels that are considered safe by public health guidelines. 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. 1
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6. Presence of interfering (extraneous) organic matter. What is Microbial Death? Inability to reproduce under optimum growth conditions. Mode of Action of Antimicrobial Agents 1.Damage to cell wall Examples: lysozyme, lysostaphin, penicillins. 2.Alteration of cell membrane Examples: polymixin-b, cepacol 3.Damage to proteins and nucleic acids Examples: radiations, alcohols, acids, and chloramphenicol. Methods of Physical Control I. High Temperature A.Moist Heat: is one of the most effective and widely 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 minutes at 100ºC,while dry heat takes 180 minutes at 140 C. Types of Moist Heat a. Steam under pressure (autoclave): it is the most practical and dependable way to destroy vegetative forms and their endospores. Autoclave is usually operated at a pressure of 15 pounds per square inch (psi) at 121ºC.
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