BIO 251 Chapter 6: Study Guide

22. What are the characteristics of bacterial colonies?

Bacterial colonies are exact copies of the original organism. They have a distinctive appearance that distinguishes one microbe from another. They must be visibly separated from one another. 1 cell can become a colony by binary fission. A colony is composed of billion of cells. Number of colonies=Number of bacterial cells in the original sample.

7. If home canning is not done properly, what type of foods (acidic or basic) would more commonly lead to botulism? Explain why.

Basic foods would lead to botulism if home canning was not done properly. Bacteria is less likely to grow in an acidic environment.

6. Are acidic foods or neutral foods more prone to food spoilage? Explain why or why not.

Neutral are more prone to food spoilage because pH is less acidic, many microbes can grow in a neutral environment.

26. After you perform a plate count, write the formula to calculate the number of bacteria in 1mL of the original sample. Practice example problems from the PowerPoint slides.

OCD = CFU/D x V OCD - Original Cell Density CFU - Colony Forming units D - Dilution factor V - Volume

28. Given the combination of positives (for example, 5-3-0), you should be able to determine the MPN.

The MPN is 110 with of 98% confidence limits of 34 (Lower) and 250 (Upper)

3. How does refrigeration or deep freezing preserve foods? Is the effect bactericidal or bacteriostatic?

The effect of refrigeration or deep freezing to preserve foods is bacteriostatic. It just means that bacteria will still be able to grow just at a very slow rate.

27. What is the advantage of filtration?

The greatest advantage of using filtration for sterilization is that very heat sensitive substances can be sterilized using this method. Some disadvantages is that it's very time consuming especially when diluting the original sample by serial dilution.

31. What is the correlation between turbidity, absorbance, and transmittance.

The more turbidity equals more absorbance and less transmittance.

30. What does turbidity in a tube represent? What is the correlation between turbidity and bacterial growth.

The turbidity represents the number of microbes. The more turbidity equals more bacterial growth.

13. What are the toxic oxygen products produced during aerobic respiration? What enzymes are produced to neutralize these toxic end products? Write their chemical reactions.

Toxic products produced: Superoxide radicals Enzymes produced: 1) Superoxide dismutase: O2- + O2- + 2H+ → H2O2 + O2 2) Catalase: 2H2O2 → 2H2O + O2

8. What is the mechanism used by H. pylori to cause gastric ulcers?

H. pylori causes gastric ulcers by damaging the protective mucus layer.

10. What is the term used for types of microbes that can survive moderate to high salt concentrations?

Halophiles

4. How does high temperature and very acidic or basic pH preserve foods? Is the effect bactericidal or bacteriostatic?

High temperature, very acidic or basic pH preserves foods by providing unfavorable conditions for bacteria to grow. They can still grow but at a lower rate known as a bacteriostatic effect.

18. What is a differential media? Give examples

It allows distinguish between groups of microorganisms by difference appearance in the media. Example: hemolysis sheep blood agar (only blood, no CNA)

19. What is a selective and differential media? Give examples

It allows growth of some types of microorganisms while inhibits others, and allow to distinguish between different types of microorganisms. Example: MSA plate, MAC plate, HEK plate

20. What is an enriched media? Give examples

It contains very nutritious substances. It is used for growing fastidious organisms (Fastidious: need specific growth factors). Example: chocolate agar used for isolation of Neisseria Gonorrhea.

17. What is a selective media? Give examples

It inhibits growth of types of microorganisms an allows others to grow. Example: Columbia CNA plate (without blood) for isolation of gram positive organisms

33. Dry weight is used to measure the growth of what type of microorganisms.

It is measured to the growth of filamentous bacteria fungi.

32. Explain how metabolic activity can be used as a growth indicator.

Metabolic activity measures the amount acids, gas, or alcohol produced. The more amount of metabolic product produced, the more number of microbes.

15. Give two reasons why agar is used as a solidifying agent in culture media and not Gelatin.

1) Gelatin liquefies at a lower temperature. 2) Certain microbes break down gelatin with the enzyme, gelatinase.

24. List the various phases of bacterial growth and explain the characteristic features of each phase.

1. LAG PHASE: No increase in cells, little or no cell division. Preparatory phase. 2. LOG PHASE or EXPONENTIAL PHASE: Bacteria is dividing rapidly during this phase by binary fission. The number of viable cells rapidly increasing. During this phase, the cells are more susceptible to drugs. 3. STATIONARY PHASE: The number of cells that are dividing is equal to the number of cells that are dying. The rate of cell division is equal to the rate of cell death. Cells die due to nutrient depletion, depletion of O2, toxic waste, and change in pH. 4. DEATH PHASE: The number of dead cells is greater than the number of viable cells. The rate of cell death is greater than the rate of cell division.

2. What is the effect of refrigeration temperature, freezing temperature, and boiling temperature on the following organisms: A. Psychrotrophs: B. Mesophiles:

A. Psychrotrophs (optimal growth: 15-25°C) -refrigeration (0-4°C): slight growth -freezing (<-18°C): dormant bacteria -boiling (>100°C): heat denatures proteins and nucleic acids B. Mesophiles (opimal growth: 20-45°C) -refrigeration (0-4°C): dormant -freezing (<-18°C): slight growth -boiling (>100°C): heat denatures proteins and nucleic acids

5. Compare the groups of microorganisms based on their pH preference. What is the preferred pH for most bacteria? What is the preferred pH for most fungi?

Acidophilies: grow best at pH of 3 Neutrophiles: neutral pH close to 7.0 Alkalophiles: pH near 8-10.5 Bacteria: are anaerobic and aerobic and generally grow in basic environments at (above pH of 7) Fungi: they require oxygen (aerobic and generally prefer an acidic environment (below pH of 7)

29. What are the advantages and disadvantages of direct microscopic count?

Advantage is that direct microscope count is very quick. Disadvantage is that the counting includes both viable cells and dead cells.

25. What are the advantages and disadvantages of the plate count method?

Any concentration of microorganism can be easily counted, if the appropriate dilution is plated. Advantage is the ability to count the number of viable cells. Disadvantage would be that it takes time for incubation up to 48 hours, 2 days or more. Plate is recommended for 30-300 colonies.

11. What are the functions of the various elements required for microbial growth?

Carbon: backbone of all organic molecules; ie. sugars, CO2, DNA/RNA Nitrogen: proteins, nucleic acids (DNA/RNA/ATP) Sulfur: proteins, biotin, thamine (Vitamin B1) Phosphorus: DNA/RNA/ATP, biological membranes (phospholipids) Trace elements: required in small amounts; function in cofactors (enzyme helpers)

16. Distinguish between chemically defined media and complex media.

Chemically Defined Media: exactly chemical composition is known; its made from pure biochemicals; it's more expensive; it's used for metabolic assays because the results are reproducible. Complex Media: made up from yeast, meat, or plants, or digests of proteins from these and other sources; exact chemical composition is not known; routine culture media in lab; examples:TSA plate, TSA medium, TSA broth

23. What is generation time? How do you calculate the total number of cells in a given population? Practice the problems in your PowerPoint slides.

Generation time is the time it takes for the original population to double. Number of cells in the original population x 2 to the power of number of generations. Important to determine the number of generations first.

9. How does high osmotic pressure created by curing and sugaring preserve foods?

Salt and sugar create a hypertonic environment because it draws water out of the cells. More solute outside than inside the cell dehydrates the cell by osmosis. No water stops metabolism. No growth, no food spoilage hence food preserved.

14. How can you distinguish between Staphylococci and Streptococci based on the catalase test?

Staphylococci: bubbling = (+) = catalase produced Streptococci: no bubbling = (-) = catalase not produced

21. What method is used to isolate pure cultures? What is a pure culture?

Streak plate method is used to isolate pure cultures. A pure culture is a culture that only has 1 organism, a culture that is isolated.

12. Compare the various groups of microbes based on their oxygen requirement. Draw and explain their growth pattern in a broth. a) Obligate Aerobes b) Obligate Anaerobes c) Facultative Anaerobes d) Aerotolerant Anaerobes e) Microaerophiles

a) Obligate Aerobes: grown in the presence of O2 b) Obligate Anaerobes: dies in the presence of O2 c) Facultative Anaerobes: grows in the presence/absence of O2; grows more with O2 because it makes ATP d) Aerotolerant Anaerobes: no effect from O2; tolerates, but does not need O2 e) Microaerophiles: needs lower amount of O2, and lesser than atmospheric O2

1. Compare the various groups of microorganisms based on their temperature requirement. Review and learn the table in your PowerPoint slides.

a. Psychrophiles: cold loving bacteria (8-15°C) b. Psychrotrophs: cold-tolerant bacteria that have the ability to grow at low temperatures (15-25°C) c. Mesophiles: organism that grows best in moderate temperature, neither too hot nor too cold (35-37°C) d. Thermophiles: bacteria that grow best at higher than normal temps. (58-65°C) e. Hyperthermophiles: extremely high environments (85-102°C)