Microbiology Chapter 9 Textbook MC and Short Answer 1 of 3

Describe three types of microbes that are extremely resistant to antimicrobial treatment, and explain why.

1. Bacterial endospores - dehydrated with hard walls .....most resistant form of life, can survive more than 20 yrs in 70% alcohol 2. Mycobacterium - contains a waxy cell wall (mycolic acid) helps survive the drying & protects from chemicals 3. Cysts of Protozoa - protozoa cysts wall prevents entry of disinfectants, protects against drying & heat.

Why are alcohols now more effective in a 70% solution than in a 100% solution?

100% alcohol will dry bacteria and not kill it

Would a chemical microbial control agent that affects plasma membranes affect humans?

A microbial agent that targets the plasma membrane of the microorganism would not be advised because humans also have a plasma membrane. For this reason, it is important to develop a microbial agent that targets components of the microorganism that are not present in the host cell. For example, penicillin is an antibiotic that targets the cell well. Since the cell wall is not present in human cells, penicillin causes no damage to the host cell.

What characteristics make surface-active agents attractive to the dairy industry?

Acid-Anionic Sanitizers: important in cleaning dairy utensils and equipment; Non-toxic; non-corrosive; and fast acting.

What are some advantages and disadvantages to using ionizing radiation to sterilize food?

Advantages - kills microbes, larvae & eggs; also kill cells that spoil or over ripen fruits & vegetables Disadvantages - Can be cancer causing & change taste & nutritional value of fruit & vegtables

Compare and contrast the action of alcohols, halogens, and oxidizing agents in controlling microbial growth.

Alcohol - denatures proteins & disrupts cell membrane (ETOH) Halogens - denatures proteins including enzymes (Cl & iodine) Oxidizing agents - denatures proteins by oxidation (hydrogen peroxide & peracetic acid)

Is Betadine an antiseptic or a disinfectant when it is used on skin?

An antiseptic. Anything that is applied to the skin will be an antiseptic and anything applied to objects is considered a disinfectant.

Hyperthemophilic prokaryotes may remain viable in canned goods after commercial sterilization. Why is this situation not dangerous to consumers?

Because hyperthermophilic microbes grow at 85 degree C and not at 37 degree C where we store our food.

Why is it necessary to use strong disinfectants in areas exposed to tuberculosis patients?

Because tuberculosis cell wall has lots of waxy lipids mycolic acid, which allows bacteria to survive drying & protects it from most water-based chemical.

Why do warm disinfectant chemicals generally work better than cool ones?

Better penetration with heat.

Why is alcohol effective against some viruses and not others?

Denature proteins, dissolve lipids Require water

Compare and contrast desiccation and lyophilization.

Desiccation - Inhibits growth by removing water that microbes need to metabolize Lyophilization - Uses freezing and drying to preserve microbes for many years, this is long term preservation of microbial culture.

Which is more likely to be used in a medical clinic laboratory, a use-dilution test or a disk-diffusion test?

Disk-diffusion test. Because this is what is used to measure the effectiveness of specific antibiotics on certain microbes. -A use-dilution test would be more appropriate in industrial uses because it measures what is the lowest amount of chemical needed in a solution to effectively kill microbes.

How is microbial growth in canned foods prevented?

Drying is often used to preserve foods (e.g. fruits, grains, etc.). Methods involve removal of water from commercial sterilization: product by heat, evaporation, freeze-drying, and addition of salt or sugar.

What chemicals are used to sterilize?

Ethylene Oxide is the gas most frequently used for sterilization.

How can campers effectively treat stream water to remove pathogenic protozoa, bacteria, and viruses?

Filtering stream Iodine tablets Adding a couple drops of Cl to 2 liters of water

Why are Gram-negative bacteria more susceptible to heat than Gram-positive bacteria?

Gram (+) bacteria has a thicker peptidoglycan layer than gram (-) & gram (-) has an outer membrane of LPS which contains lipid A

Describe 5 physical methods of microbial control.

Moist Heat - use to disinfect, sanitize, sterilize & pasteurize, kills cells by denaturing protein & destroying cytoplasmic membrane (disinfecting baby bottles) Dry heat - Used w/ powders, oils & metals. Hot air is used to denature protein & foster oxidation of metabolic & structural chemical. Refrigeration & Freezing - Used in food preparation & storage. Halts growth of most pathogens, because chemical reactions occur slower at lower temperatures. Ionizing radiation - denatures molecules DNA, which causes cell death & mutations Osmotic pressure - high concentration of salt & sugar. Used to preserve food like salted fish. Desiccation & Lyophilzations - technique combining freezing & drying

Defend the following statement: "Pasteurization is not sterilization."

Pasteurization allows thermophilic & thermoduric bacteria to survive (not pathogenic) & sterilization kills all microbes

Compare and contrast four tests that have been developed to measure the efficacy of disinfectants.

Phenol coefficient - Oldest method/efficiency against phenol; the greater the ratio the better Kelsey-Sykes capacity - Use in Europe/bacterial suspension added to chemical, lack of turbidity is lack of bacterial growth In-use - Checks real life situations/swab from a suspected site to media and check for growth, most realistic to determining efficacy of chemical Use - Use in US/Dip metal cylinders into broth culture of bacteria & dry 36 degree C

What chemical disinfectants can be considered sporicides?

Phenols; Glutaraldehyde; B-Propiolactone; Ethylene oxide ;Peroxy acids

Usual definition of sterilization is the removal or destruction of all forms of microbial life; how could there be practical exceptions to this simple definitions?

Prions have a high resistance to all forms of sterilization; sterilization implies to the absence of prions.

How is it possible that a solution containing a million bacteria would take longer to sterilize than one containing a half-million bacteria?

Rate of microbial death: The number of microbes. The more microbes to begin with, the longer it takes to eliminate the entire population. other factors: environment influences; time of exposure; microbial characteristics.

Why would a can of pork take longer to sterilize at a given temperature than a can of soup that also contained pieces of pork?

Solid foods heat unevenly because of the uneven distribution of moisture.

The presence or absence of endospores has an obvious effect on microbial control, but why are gram-negative bacteria more resistant to chemical biocides than gram-positive bacteria?

The characteristics of the gram-negative bacteria makes it more susceptible to chemical biocides due to it's physical characteristics. form endospores during adverse conditions; waxy lipid like membrane; thick cells. Mycobacteria, endospores, and protozoan cysts and oocysts are very resistant than enveloped viruses to disinfectants and antiseptics.

What is the difference between thermal death point and thermal death time?

Thermal death point is the lowest temperature that kills all cells in broth in 10 min Thermal death time is the time that it takes to sterilize volume of liquid at a set temperature.

What is the connection between the killing effect of radiation and hydroxyl radical forms of oxygen?

These radicals are produced from ionizing radiation that take electrons from other molecules.

Contrast the structures and actions of soaps and quats.

They are both detergents. SOAPS do not kill organism, they are washed off surfaces & QUATS disrupt cellular membrane where the affected cell lose internal ions

1. In practical terms in everyday use, which of the following statements provides the definition of sterilization? a. Sterilization eliminates organisms and their spores or endospores. b. Sterilization eliminates harmful microorganisms and viruses. c. Sterilization eliminates prions. d. Sterilization eliminates hyperthermophiles.

a. Sterilization eliminates organisms and their spores or endospores.

6. The endospores of which organism are used as a biological indicator of sterilization? a. Bacillus stearothermophilus b. Salmonella enterica c. Mycobacterium tuberculosis d. Staphylococcus aureus

a. bacillus stearothermophilus

13. Biosafety Level 3 includes a. double sets of entry doors. b. pressurized suits. c. showers in entryways. d. all of the above

a. double sets of entry doors

10. Which of the following types of radiation is more widely used as an antimicrobial technique? a. electron beams b. visible light waves c. radio waves d. microwaves

a. electron beams

17. Which of the following disinfectants acts against cell membranes? a. phenol b. peracetic acid c. silver nitrate d. glutaraldehyde

a. phenol

20. Which class of surfactant is most soluble in water? a. quaternary ammonium compounds b. alcohols c. soaps d. peracetic acids

b. alcohols

2. Which of the following substances or processes kills microorganisms on laboratory surfaces? a. antiseptics b. disinfectants c. degermers d. pasteurization

b. disinfectants

16. Which of the following chemicals is active against bacterial endospores? a. copper ions b. ethylene oxide c. ethanol d. triclosan

b. ethylene oxide

14. A sample of E. coli has been subjected to heat for a specified time, and 90% of the cells have been destroyed. Which of the following terms best describes this event? a. thermal death point b. thermal death time c. decimal reduction time d. none of the above

c. decimal reduction time

9. The preservation of beef jerky from microbial growth relies on which method of microbial control? a. filtration b. lyophilization c. desiccation d. radiation

c. desiccation

15. Which of the following substances is least toxic to humans? a. carbolic acid b. glutaraldehyde c. hydrogen peroxide d. formalin

c. hydrogen peroxide

8. Which of the following items functions most like an autoclave? a. a boiling pan b. an incinerator c. a microwave oven d. a pressure cooker

d. a pressure cooker

18. Which of the following disinfectants contains alcohol? a. an iodophor b. a quat c. formalin d. a tincture of bromine

d. a tincture of bromine

4. The microbial death rate is used to measure a. the efficiency of a detergent. b. the efficiency of an antiseptic. c. the efficiency of sanitization techniques. d. all of the above

d. all of the above

5. Which of the following statements is true concerning the selection of an antimicrobial agent? a. An ideal antimicrobial agent is stable during storage. b. An ideal antimicrobial agent is fast acting. c. Ideal microbial agents do not exist. d. all of the above

d. all of the above

12. Which of the following adjectives best describes a surgical procedure that is free of microbial contaminants? a. disinfected b. sanitized c. degermed d. aseptic

d. aseptic

19. Which antimicrobial chemical has been used to sterilize spacecraft? a. phenol b. alcohol c. heavy metal d. ethylene oxide

d. ethylene oxide

11. Which of the following substances would most effectively inhibit anaerobes? a. phenol b. silver c. ethanol d. hydrogen peroxide

d. hydrogen peroxide

7. A company that manufactures an antimicrobial cleaner for kitchen counters claims that its product is effective when used in a 50% water solution. By what means might scientists best verify this statement? a. disk-diffusion test b. phenol coefficient c. filter paper test d. in-use test

d. in-use test

3. Which of the following terms best describes the disinfecting of cafeteria plates? a. pasteurization b. antisepsis c. sterilization d. sanitization

d. sanitization

If you wanted to disinfect a surface contaminated by vomit and a surface contaminated by a sneeze, why would your choice of disinfectant make a difference?

no single chemical is good for all applications. It would depend on what the situation dictates. Use of Biguanides would be useful on the sneeze because of chlorhexidine.