Lesson 1

Question 1

What is binary fission?

Answer 1

A method of bacterial division leading to an increase in cell mass, duplication of genome, and separation of cell membrane and cell wall.

The original mother cell and daughter cells are identical.

Question 2

What does bacterial growth refer to?

Answer 2

A change in the population rather than an increase in the size or mass of individual bacteria.

Question 3

What occurs during the lag phase of bacterial growth?

Answer 3

Population remains unchanged; cells may grow in volume or mass, synthesizing enzymes, proteins, RNA, and increasing metabolic activity.

Question 4

What characterizes the exponential growth phase?

Answer 4

The rate of division is greater than the rate of cell death, expressed as generation time or doubling time.

Question 5

What limits population growth in the stationary phase?

Answer 5

Exhaustion of nutrients, accumulation of inhibitory metabolites or end products, and exhaustion of space.

Question 6

What occurs during the death phase of bacterial growth?

Answer 6

The bacterial population declines when the rate of bacterial death exceeds cell division.

Question 7

How is population increase calculated during the exponential growth phase?

Answer 7

Using the formula b = 1 x $2^n$, where ‘n’ is the number of generations.

Question 8

What is a chemostat?

Answer 8

A bioreactor where fresh medium is continuously added and culture is continuously removed to maintain constant volume.

Question 9

What are chemotrophs?

Answer 9

Organisms that use chemical compounds as an energy source.

Question 10

What defines phototrophs?

Answer 10

Organisms that use radiant energy (light) for energy.

Question 11

What are lithotrophs?

Answer 11

Organisms that obtain electrons from reduced inorganic compounds.

Question 12

What are organotrophs?

Answer 12

Organisms that use organic compounds as a source of electrons.

Question 13

What are the nitrogen sources for bacterial growth?

Answer 13

Atmospheric nitrogen, inorganic nitrogen (nitrates, nitrites, ammonium salts), and organic compounds (amino acids).

Question 14

What are autotrophs?

Answer 14

Organisms that use CO₂ as their major source of carbon.

Question 15

What are heterotrophs?

Answer 15

Organisms that use organic compounds as their source of carbon.

Question 16

What is the optimum growth temperature for bacteria that cause disease in humans?

Answer 16

37-39°C.

Question 17

What is the optimum pH for bacterial growth?

Answer 17

6.5-7.5, with limits of 5-9.

Question 18

What is the impact of extreme pH on microbial growth?

Answer 18

Extreme pH prevents microbial growth.

Question 19

What does water activity ($Aw$) estimate?

Answer 19

The proportion of uncomplexed water available in a formulation.

Question 20

What is the limiting Aw value for Gram-Negative rods?

Answer 20

0.95.

Question 21

What is the limiting Aw value for most yeast?

Answer 21

0.88 (down to 0.73).

Question 22

Fill in the blank: _______ are tolerant to low levels of oxygen.

Answer 22

Tolerant anaerobes

Question 23

True or False: Obligate anaerobes can use oxygen for growth.

Answer 23

False

Question 26

What method only counts live bacteria?

Answer 26

Viable count method ## Footnote This method estimates the number of colony-forming units (cfu) based on the assumption that one bacterium gives rise to one colony.

Question 27

What is the viable count referred to?

Answer 27

Number of colony-forming units (cfu) ## Footnote The viable count assesses the number of live bacteria capable of forming colonies.

Question 28

What factors can alter bacterial growth and colony formation?

Answer 28

Type of medium used and conditions of incubation ## Footnote Different media and incubation conditions can significantly affect the results of bacterial culture.

Question 29

List the plate count methods.

Answer 29

* Pour plate * Spread plate method * Any other methods must be validated ## Footnote These methods are used to quantify viable bacteria in a sample.

Question 30

What is the purpose of serial dilutions in colony counting?

Answer 30

To count the number of colonies ## Footnote Serial dilutions help to reduce the concentration of bacteria for accurate counting.

Question 31

What type of membrane filters are used in membrane filtration?

Answer 31

0.45 μm membrane filters ## Footnote These filters are used to separate bacteria from liquids.

Question 32

What are cellulose nitrate filters used for?

Answer 32

Aqueous, oily, and weakly alcoholic solutions ## Footnote Cellulose nitrate filters are suitable for various types of solutions in membrane filtration.

Question 33

What are cellulose acetate filters used for?

Answer 33

Strongly alcoholic solutions ## Footnote These filters are specifically designed to handle alcohol-rich environments.

Question 34

What is the Most Probable Number (MPN) method used for?

Answer 34

Enumeration of bacteria in situations where no other method is available ## Footnote MPN is a statistical method used for estimating the concentration of viable microorganisms.

Question 35

What is the first step in the MPN method?

Answer 35

Prepare a series of at least three subsequent tenfold dilutions of the product ## Footnote This step is crucial for assessing the concentration of bacteria in a sample.

Question 36

How many aliquots are used to inoculate tubes in the MPN method?

Answer 36

Three aliquots ## Footnote Each aliquot typically consists of 1g or 1ml of the sample.

Question 37

What is the incubation temperature for the MPN method?

Answer 37

30°C to 35°C ## Footnote This temperature range is optimal for microbial growth during the incubation period.

Question 38

What does the total count method measure?

Answer 38

Counts both live and dead bacteria ## Footnote This method provides a comprehensive count of all bacteria present in a sample.

Question 39

What is one method for direct cell count?

Answer 39

Microscopy or electronic particle counter ## Footnote Direct observation or automated counting can be used to determine cell numbers.

Question 40

How can cell mass be measured?

Answer 40

* Directly by weighing * Measurement of cell nitrogen * Measurement of dry weight (oven) ## Footnote These methods provide an estimate of the biomass present in a sample.

Question 41

What does spectrophotometric measurement assess?

Answer 41

Turbidity and optical density ## Footnote This method evaluates how light interacts with a bacterial population to estimate concentration.

Question 42

What does cell activity measurement relate to?

Answer 42

Degree of biochemical activity to the size of population ## Footnote This indirect method correlates metabolic activity with bacterial numbers.