Experiment three Physical and Chemical agents for the Control of microorganisms Effect of Ultraviolet Radiation Effect of chemical agents

Effect of Ultraviolet Radiation Ultraviolet radiation (UV, 240-300nm) The most effective wavelengths: 265nm Mechanism: destroy bacteria by interfering with DNA replication and transcription during protein synthesis Characteristics: poor penetration damage of the eyes and the skin.

Effect of Ultraviolet Radiation MATERIALS: Media: Nutrient agar plate Culture:18-24 hours cultures of Escherichia coli Alcohol burner , inoculating loop, cotton swab .

Effect of Ultraviolet Radiation PROCEDURE: Take a nutrient agar plate, streak E.coli intensively on the plate. Place the plate directly under the ultraviolet lamp. The plate lid cover half part of the agar surface. After exposed to ultraviolet light for 30minutes,close the plate.Incubate the plate in an inverted position at 37℃ for 18 to 24 hours and observe the results. RESULT: Observe the growth of bacterium in the plate. .

Effect of chemical agents Mechanisms of action -- Destroy cell membranes; e.g., surfactants/detergents -- dissolve lipids -- Denature bacterial proteins (e.g., enzymes ); Interfere bacterial metabolism -- Damage genetic materials (DNA, RNA); e.g., formaldehyde.

Effect of chemical agents Commonly used chemical agents ---Phenol ---Soaps and detergents ---Alcohols: 70-75%(medical use) ---Heavy metals: Silver nitrate (1%) ---Chlorine ---Iodine ---Aldehydes: 37%, Formalin ---Dyes: crystal violet

Effect of chemical agents Reagents: 1. 1% crystal violet 2. 2% mercurochrome 3. 5% iodine 4. 0.1% bromogeramine 5. normal sodium Species： S.aureus 1 agar plate E.coli 1 agar plate

Effect of chemical agents PROCEDURE: Using Sterile techniques, incubate the agar plate with the culture of S.aureus (or E.coli) by streaking the agar plate in horizontal and vertical directions with an inoculating loop Using a flamed and cooled forceps, take each saturated disc and place it in the appropriately labeled area respectively to ensure that each one ie at the middle point of radius and of them are equidistant from each other. Gently press each disk down so that they adhere to the surface of the agar. Label and incubate all plate culture in an inverted position at 37℃ for 18-24 hours.

iodine normal sodium bromogeramine mercurochrome crystal violet

Effect of chemical agents RESULT: Measure inhibition zone – diameter or 2× radius

Diameter of Inhibition Zone (mm) Inhibition zone diameter (mm) >15mm 10~15mm <10mm 0mm susceptibility degree Extremely sensitive Medium sensitive Slight sensitive restistant Record: Cultures Diameter of Inhibition Zone (mm) crystal violet mercurochrome iodine bromogeramine normal sodium S.Aureus E.coli Susceptibility degree

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