Exam 2 will be on Wednesday, March 27, 2019 .

1. Exam 2 will be on Wednesday, March 27, 2019. Place: If your last name starts with A – Pe: please take exam in room 112 Gregory If your last name starts with Ph – Z: please take exam in room 213 Gregory Covers chapters: 5, 6, 5, 7, 5, 9 &10 and 5 Review Session: 7:00 – 8:20 pm, Monday, March 25 Place: Room 124 Burrill Hall

2. MCB 100 Introductory Microbiology 2019 Chapter 9 from Microbiology by Bauman Physical and Chemical Antimicrobial Agents Treatments & Substances That Kill or Inhibit Microbes physical agents: heat, cold, radiation, desiccation (drying) chemicals: detergents, solvents, oxidizing agents, metals

3. Filtration Can Be Used To Sterilize a Liquid(sterilizes without heat) * Bacteria are generally larger than 0.5 mm in diameter, if you put a fluid through a filter with a pore size of 0.2 mm, the bacteria will be trapped. * Filtration is used when the product may be degraded by heat. * Examples of solutions that are filter sterilized include: vitamin solutions, some amino acids and cold-filtered beer.

4. Killing Microorganisms With Radiation Two types of radiation used in antimicrobial applications are: UV light and ionizing radiation. UV light is used to kill bacteria in aquariums and on the surface of instruments or lab bench tops. Germicidal lamps emit UV light. UV light damages DNA and increases the frequency of mutations.

5. UV RADIATION UV light causes formation of pyrimidine dimers in DNA that can lead to the introduction of point mutations if the DNA polymerase attempts to replicate the damaged DNA before the repair enzymes can fix the damage.

6. This laminar flow hood for tissue culture work includes a germicidal UV lamp. Pyrimidine Dimer Formation at TT and TC sequences.

7. UV Damage to DNA Pyrimidine dimers can be formed at TT, TC and CT sequences. There are repair mechanisms that can fix the damaged DNA, but one system tends to introduce errors that can cause mutations. UV-damaged DNA leads to activation of the SOS-response.This is an error-prone DNA repair mechanism that fixes the damaged strand of DNA but increases the probability of point mutations.

8. Killing Microorganisms With Radiation Ionizing radiation (gamma rays, x-rays)damages DNA.Irradiation is used to kill microorganisms on some foods including: strawberries, beef and poultry. Ionizing radiation may have less effect on the taste and texture of the food product than traditional treatments that involve heat. Food does not become radioactive when it is treated with radiation.

9. IONIZING RADIATION Ionizing irradiation, such as gamma-rays and x-rays can cause breaks in the backbone chain of a DNA molecule. This can cause large deletion mutations to occur.

10. REVIEWUV & IONIZING RADIATION UV light causes formation of pyrimidine dimers in DNA that can lead to the introduction of point mutations if the DNA polymerase attempts to replicate the damaged DNA before the repair enzymes fix the damage. Ionizing irradiation can cause breaks in the backbone chain of a DNA molecule.

11. Radiation Which ONE of the following statements about using radiation as an antimicrobial agent is FALSE?A. Irradiation of a sample with either UV-light or ionizing radiation will cause the sample to become radioactive. B. UV-light usually causes point mutations in DNA. C. Ionizing radiation can cause double-stranded breaks in DNA that may lead to large deletion mutations. D. Ionizing radiation has the ability to penetrate biological samples more deeply than UV-irradation. E. Traditional heat-based canning methods damage the taste and vitamin content of fruits and vegetables more than sterilization by ionizing radiation.

12. Radiation Which ONE of the following statements about using radiation as an antimicrobial agent is FALSE?A. Irradiation of a sample with either UV-light or ionizing radiation will cause the sample to become radioactive. B. UV-light usually causes point mutations in DNA. C. Ionizing radiation can cause double-stranded breaks in DNA that may lead to large deletion mutations. D. Ionizing radiation has the ability to penetrate biological samples more deeply than UV-irradation. E. Traditional heat-based canning methods damage the taste and vitamin content of fruits and vegetables more than sterilization by ionizing radiation.

13. Controlling the Growth of Microorganisms Using Osmotic Pressure When a microorganism is placed in a hypertonic environment, water will flow out of the cytoplasm. (low water activity) If the cell becomes dehydrated enough, the cytoplasm can shrink and the cell membrane can separate from the cell wall. This can kill the bacterium. Thus a high concentration of salt or sugar in a food or beverage can prevent microbial growth. (bacteriostatic) This is why honey, syrup, beef jerky and salt pork do not have to be refrigerated.

14. Maple syrup doesn’t spoil when stored at room temperature because the sugar concentration is so high that the water activity is low enough to prevent microbial growth. Raisins and beef jerky are examples of dried foods. Again the low water activity inhibits microbial growth and that helps to prevent spoilage.

15. A. B.

16. Antiseptics, Disinfectants and Sanitizing Agents Antiseptics & disinfectants are chemical agents used to kill bacteria. The difference is that an antiseptic is used on human skin and mucous membranes whereas a disinfectant is used on inanimate objects like table tops. A sanitizing agent is a disinfectant that is also a detergent, it is used to clean and disinfect an object. The properties of an ideal disinfectant 1. selective toxicity, lethal to bacteria but not harmful to humans 2. good solubility in water 3. stable at room temperature 4. toxicity at room temperature, able to kill bacteria without adding heat 5. capacity to penetrate 6. non-corrosive 7. non-staining 8. not offensive (no bad smell)

17. Disinfectants - Mechanisms of Killing Action Solvents examples: Phenols, Cresols and Alcohols - denature proteins and disrupt the cytoplasmic membrane structure Soaps and Detergents examples: quaternary ammonium compounds (quats) - can denature proteins and disrupt the cytoplasmic membrane structure, but they are weak and mostly just act to help clean a surface

19. Soaps and Detergents A soap is a salt of a fatty acid whereas a detergent is a synthetic derivative of a fatty acid. Detergents are more soluble in water than soap and less likely to leave a soap scum. Quaternary ammonium salts (quats) are examples of detergents. Disinfectant cleansers often contain quats such as benzalkonium chloride. Soaps and detergents have a mild killing power against bacteria. They are surfactants that reduce the surface tension of water and increase the solubility of oily particles. This makes it easier to wash bacteria off of the skin and may kill a few of them by disrupting cell membranes. Some bacteria are resistant to being killed by soaps and detergents and may use the soap or detergent as a carbon source if the agent is at a low concentration.

20. Disinfectants - Mechanisms of Killing Action Oxidizing Agents examples: Halogens, Bleach, Hydrogen Peroxide and the sterilizing gas Ethylene Oxide - oxidation of organic compounds Skin after short exposure to 35% hydrogen peroxide.

21. Disinfectants - Mechanisms of Killing Action Heavy Metals examples: mercury, Hg2+ lead, Pb2+ silver, Ag Mechanism of action - inhibition of enzymes (protein denaturation) divalent heavy metal ions displace monovalent ions such as sodium and potassium mercury ions associating with carboxyl and amino groups from a protein

22. Disinfectants - Mechanisms of Killing Action Aldehydes examples: glutaraldehyde and formaldehyde aldehydes react with proteins and forms cross-links that inactivate enzyme and may cause a protein to precipitate Gaseous Sterilants examples: ethylene oxide, propylene oxide - strong alkylating agent that damages DNA and proteins Acids and Bases are of limited usefulness due to corrosive activity The aldehyde groups of glutaraldehyde react with amines, amides and sulfhydryl groups in proteins.This can cause the cross-linking and precipitation of proteins.

23. Chapter 9 Review - Controlling Microorganisms Regarding the control of Microorganisms using physical methods: choose the TRUE statement. A. Passing a liquid through a filter with a pore size of 0.2 microns will trap all known types of bacterial cells but not viruses. B. Germicidal lamps use ionizing radiation to sterilize materials. C. UV-radiation can penetrate farther into a biological sample than ionizing irradiation can. D. Treatment of a food product with ionizing radiation will cause the food to become radioactive.

24. Chapter 9 Review - Controlling Microorganisms Regarding the control of Microorganisms using physical methods: choose the TRUE statement. A. Passing a liquid through a filter with a pore size of 0.2 microns will trap all known types of bacterial cells but not viruses. B. Germicidal lamps use ionizing radiation to sterilize materials. C. UV-radiation can penetrate farther into a biological sample than ionizing irradiation can. D. Treatment of a food product with ionizing radiation will cause the food to become radioactive.

25. Antiseptics and Disinfectants • Which statement about controlling microorganisms using disinfectants and antiseptics is FALSE? • Organic solvents and soaps can disrupt the structure of a cell membrane. • B. Soaps and detergents are composed of amphipathic molecules that are partiallyhydrophillic and partially hydrophobic like a lipid. • C. Heavy metals such as mercury and silver can be used to kill bacteria but these substances are not toxic to human cells. • D. Bleach ingredients such as sodium hypochlorite and hydrogen peroxide can cause the oxidation of a wide variety of organic compounds.

26. Antiseptics and Disinfectants • Which statement about controlling microorganisms using disinfectants and antiseptics is FALSE? • Organic solvents and soaps can disrupt the structure of a cell membrane. • B. Soaps and detergents are composed of amphipathic molecules that are partiallyhydrophillic and partially hydrophobic like a lipid. • C. Heavy metals such as mercury and silver can be used to kill bacteria but these substances are not toxic to human cells. • D. Bleach ingredients such as sodium hypochlorite and hydrogen peroxide can cause the oxidation of a wide variety of organic compounds.