اثر عوامل فیزیکی و شیمیایی بر باکتری ها گروه ميكروب شناسي دكتر مهاجري

Definitions Sterilization: total inactivation of the all forms of microbial life Suffix –stasis: the organism is merely inhibited in growth or multiplying Suffix –cide: a killing action Suffix –lytic: destroyed

Bactericide: kills bacteria Germicide (disinfectant): kills microorganisms capable of producing an infection Bacteriostatic: prevents the growth of bacteria agents often binds reversibly to ribosomes Bacteriolytic : detergents and cell wall synthesis inhibitors Antiseptic: oppose sepsis or putrefaction either by killing microorganisms or by preventing their growth (used for agents that are applied topically to living tissues)

Antimicrobial chemical agents Factors affecting disinfectant potency: - concentration of agents - time - pH - temperature - nature of the organism - presence of extraneous material

Evaluation of disinfectants phenol coefficient Classic phenol coefficient test: a tube dilution procedure designed to determine the ratio of the highest dilution of the germicide that will kill the test organism within a specified time to the greatest dilution of phenol showing the same results. with 3 bacterium →Salmonella typhi Staphylococcus aureus Pseudomonas aeruginosa

Mechanism of antimicrobial action 1) agents that damage the cell membrane e.g.: organic solvents, detergents  surface-active disinfectants - cationic agents: Quaternary Ammonium Compounds (QAC), Zephiran - anionic agents: soaps, Triton - nonionic agents: Tween 80

 Phenolic compounds - at low concentration are rapidly bactericidal (5%) - for testing of new bactericidal agents - e.g.: cresols, diphenyl compounds  Alcohols Ethanol: I. Ethanol: to clean the skin prior injection to disinfection of clinical thermometers active against G+ve, G-ve, AFB is most effective at a con. of 50-70%

Isopropyl alcohol II. Isopropyl alcohol advantages ??? disadvantages ??? 2) agents that denature proteins e.g.: acids, alkalines, alcohols, acetone, other organic solvents

3) agents that modify functional groups of proteins and nucleic acids have mercury and arsenic e.g.: formaldehyde, anionic detergents, acid dyes, basic dyes, QAC, cationic detergents Heavy metals I. Heavy metals - mercurials - silver compounds (AgNO3) oxidizing agents II. oxidizing agents (-SH enzyme → S-S) e.g.: Chlorine, Iodine, Hydrogen Peroxide

Dyes III. Dyes - Triphenylmethane dyes: crystal violet, brilliant green, malachite green - Acridine dyes: interfere with the synthesis of nucleic acids and proteins in both bacterial and mammalian cells intercalation interact with ds helical DNA by intercalation e.g.: Proflavine, Acriflavine detail mechanism of acridine orange ???

Alkylating agents IV. Alkylating agents e.g.: - 37% formaldehyde (formalin) > react with a sulfydryl group of enzyme - glutaraldehyde > bind to sulfydryl or amino groups - ethylene oxide > active against spore, TB bacillus but is slow action, used for heat sensitive materials such as polyethylene tubes, electronic and medical equipments, drugs

Antimicrobial physical agents 1) Heat proteins denature and coagulate proteins membrane loss of functional integrity of the membrane two types:  moist heat - autoclave - pasteurization (62°C-30 min or 71°C-15 s) reduces microbial population in milk and other heat-sensitive liquids

controls Listeria, Campylobacter, Salmonella, E. coli, etc

Autoclave Typical cycle - 121ºC, 15 minutes, 105 KPa At 134 ºC 3 minutes is required Heat denatures proteins – easier in the presence of moisture – disrupts hydrogen bonds. Must be no air present

 dry heat

2) Freezing routine method for preserving bacteria (lyophilization = freeze drying) not reliable method of sterilization ice crystal formation 3) Radiation sunlight, UV, x-ray, γ-ray bactericidal range is nm (max 260nm = max absorption of DNA) → DNA damage

UV radiation

thymine dimer formation → inhibition of DNA synthesis mutagenic effects ionizing radiation used for medical supplies and food

4) Ultrasonic and Sonic Vibration 5) Filtration sterilization of heat–labile materials (serum, plasma, trypsin) with membrane filters pore size range: µm most widely use: 0.22 µm High-efficiency particulate air (HEPA) filters

Filtration For heat sensitive liquids – vaccines, drugs Dependent on pore size of filter

Other Methods Tyndalization Pasteurization

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