Question 1

Which group of microbes is most likely to grow optimally at refrigerator temperatures (around 4°C)?

Accepted Answer

Psychrophiles

Question 2

Why are hyperthermophiles that grow above 100°C seemingly limited to oceanic depths?

Accepted Answer

Because pressure at oceanic depths prevents water from boiling at 100°C

Question 3

What is the main advantage of using phosphate salts as buffers in microbial growth media, aside from controlling acidity?

Accepted Answer

They are non-toxic and provide essential phosphorus for cell growth

Question 4

Why might people have used techniques that rely on osmotic pressure for food preservation before modern methods?

Accepted Answer

High osmotic pressure causes plasmolysis, inhibiting microbial growth

Question 5

If bacterial cells are given a sulfur source containing radioactive sulfur ($$^{35}S$$), in which molecules would the $$^{35}S be $$found?

Accepted Answer

Proteins containing sulfur amino acids

Question 6

How would you determine whether a microbe is a strict anaerobe?

Accepted Answer

Grow it in the presence of oxygen and observe if it survives

Question 7

What is the most obvious way for a microbe to avoid damage by toxic forms of oxygen?

Accepted Answer

Produce enzymes like superoxide dismutase and catalase

Question 8

How does biofilm formation benefit a pathogen?

Accepted Answer

It allows the pathogen to resist environmental stresses and immune responses

Question 9

Which type of culture medium is EMB agar, which contains methylene blue to inhibit gram-positive bacteria and allows lactose-fermenting bacteria to produce colored colonies?

Accepted Answer

Selective and differential medium

Question 10

Why is it difficult to measure the growth of filamentous mold isolates by the plate count method?

Accepted Answer

Filamentous molds do not form discrete colonies

Question 11

Which equation correctly represents the breakdown of hydrogen peroxide by catalase?

Accepted Answer

$$2H_2O_2 \rightarrow 2H_2O + O_2$

Question 12

A bacterial population increases from 10,000 to 10,000,000 cells in four hours. What is the generation time? Use the formula $$G = \frac{t}{3.3 \log \frac{A}{a}}$$ where $$t is $$time, $$A is $$final cell number, and $$a is $$initial cell number.

Accepted Answer

24 minutes

Question 13

Which biosafety level (BSL) is appropriate for working with pathogens that can cause serious or potentially lethal disease and require maximum containment?

Accepted Answer

BSL-4

Question 14

Which method is most appropriate for estimating bacterial numbers in a sample when the bacteria will grow in a liquid differential medium, such as coliforms in water testing?

Accepted Answer

Most probable number (MPN) method

Question 15

Why is turbidity more useful for measuring contamination of liquids by large numbers, rather than small numbers, of bacteria?

Accepted Answer

Turbidity is only visible when more than a million cells per milliliter are present

Question 16

Which phase of bacterial growth is characterized by equilibrium between cell division and cell death?

Accepted Answer

Stationary phase

Question 17

What is the main reason that colonies do not grow to infinite size or fill the entire Petri plate?

Accepted Answer

Nutrient depletion and accumulation of waste products limit growth

Question 18

Which of the following is a direct method of measuring cell growth?

Accepted Answer

Plate count method

Question 19

Why is the prevention of biofilms important in a healthcare environment?

Accepted Answer

Biofilms can break off and cause infections

Question 20

Which equation represents the conversion of superoxide to oxygen and hydrogen peroxide by superoxide dismutase?

Accepted Answer

$$2O_2^- + 2H^+ \rightarrow O_2$ + H_2O_2$$

Microbial Growth: Physical and Chemical Requirements, Culture Techniques, and Measurement Methods

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