BISC300 Lecture Notes - Lecture 11: Gamma Ray, Bactericide, Heavy Metals
22 May 2018
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Lecture 11: Antimicrobial Mode of Action
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• Heat is lethal to microorganisms. The rate microbial cells are killed depends on several
factors. Select the most comprehensive answer.
o The concentration of the microbes to be destroyed
o Temperature of exposure
o Time required at this temp to accomplish the desired rate of destruction
• Decimal reduction time at 80 degrees Celsius for Salmonella is 5 minutes. How many
cells will be left after 10 minutes in a sample that started with 5000 cells.
o 50
• Pasteurization is a process that
o Preserves nutritional properties of the liquid
o Slows spoilage
• UV radiation
o Has bactericidal properties
o Causes DNA damage
o Works effectively only on surfaces (weak form of radiation)
• In order to preserve active ingredients solution of antibiotics should be sterilized using
o ionizing radiation
• chemical antimicrobial agents affect growth of microbes because they
o denature proteins
o …
o …
• Heavy metals (ions of mercury, arsenic, and zinc)
o Act on proteins
o Are toxic
• Intermediate level disinfectants destroy
o …
o …
• If a bacterial sample came from an island that has never been populated by humans
o Few bacteria could be resistant to antibiotic even though they were never
exposed to it
Ultraviolet (UV) radiation
• 260 nm – most bactericidal (DNA absorbs)
o Why?
• Limitation – surface sterilization
o Poor penetration
o Has been used for water treatment
Ionizing Radiation
• Gamma radiation is powerful, deep penetration
• Destroyes bacterial endospores
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Document Summary
Lecture 11: antimicrobial mode of action: heat is lethal to microorganisms. The rate microbial cells are killed depends on several factors. If a bacterial sample came from an island that has never been populated by humans: few bacteria could be resistant to antibiotic even though they were never exposed to it. Ultraviolet (uv) radiation: 260 nm most bactericidal (dna absorbs, why, limitation surface sterilization, poor penetration, has been used for water treatment. Ionizing radiation: gamma radiation is powerful, deep penetration, destroyes bacterial endospores, not always effective against viruses, used for sterilization and pasteurization of, antibiotics, hormones, sutures, plastic disposable supplies food. Harvard experiment: observations, one e. coli cell mutates to survive in its surroundings and colonizes in the higher concentration of antibiotic. Antimicrobial drugs: spectrum of activity, effect on bacteria, mode of action. Antibiotics: bacteriostatic: slows growth of bacteria, bactericidal: kills bacteria.
