Bacterial Population Growth

Question 1

What is the bacterial cell cycle?

Answer 1

1: cell elongates, enlarging its volume and DNA is replicated
2:cell wall + plasma membrane begin to constrict
3: cross-wall forms, separating the 2 DNA copies
4: cells separate

Question 2

What is critical to control and prevention in bacterial growth?

Answer 2

Understanding bacterial growth

This includes environmental microbial contamination, infectious disease caused by bacteria, and pharmaceutical spoilage.

Question 3

What are the four sequential phases of bacterial population growth?

Answer 3

• Lag phase
• Log (or exponential) phase
• Stationary phase
• Death phase

Each phase represents a different stage in the growth cycle of bacterial populations.

Question 4

What happens in the lag phase?

Answer 4

• Little or no cell division occurs
• Intense metabolic activity. Individual cells increase in size

Question 5

What happens in the log/ exponential phase?

Answer 5

• Rapid and constant population growth (exponential manner)
• Number of cells produced > Number of cells dying

Question 6

What happens in the stationary phase?

Answer 6

• Population size begins to stabilise
• Number of cells produced = Number of cells dying

Question 7

What is the death phase?

Answer 7

• Population size begins to decrease
• Number of cells produced < Number of cells dying

Question 8

What is the generation time in bacterial growth?

Answer 8

Time required for a bacteria to complete the cell cycle
*number of bacteria doubles each generation

For example, E. coli divides every 20 minutes, while some bacteria like M. tuberculosis require over 24 hours.

Question 9

What are biofilms?

Answer 9

Microbial communities embedded within extracellular polymeric substances

Biofilms can shield bacteria from external factors and facilitate nutrient exchange.

Question 10

What do biofilms do?

Answer 10

▪ Shields bacteria from external factors (e.g.
antibiotics cannot diffuse through it)
▪ Facilitates nutrient exchange
▪ Enables microbes to attach various surfaces

Question 11

What are the physical requirements for bacterial growth?

Answer 11

*temperature
*pH
*Water activity

Question 12

What are the chemical requirements for bacterial growth?

Answer 12

*carbon source
*organic growth factors
*oxygen
*nitrogen,sulphur and phosphate
*ions + trace elements

Question 13

What type of bacteria are psychrophiles?

Answer 13

Cold-loving bacteria that thrive below 15°C

These bacteria have specific temperature requirements for growth.

Question 14

What type of bacteria are psychrotrophs?

Answer 14

Grow at 20-30℃ but can tolerate colder temperatures

Question 15

What type of bacteria are mesophiles?

Answer 15

“Middle loving” bacteria with an optimal range of 25-40℃ (most human pathogens)

Question 16

What type of bacteria are thermophiles?

Answer 16

“Heat loving” bacteria with an optimal range of 50-60℃

Question 17

What pH range do acidophiles thrive in?

Answer 17

pH < 5.5

Acidophiles are adapted to acidic environments.

Question 18

What pH range do neutrophils thrive in?

Answer 18

(most pathogens)
pH 6.5-7.5

Question 19

What pH range do alkaliphiles thrive in?

Answer 19

(rare)
pH >8.0

Question 20

What is the osmotic pressure’s effect on bacterial cells in a hypertonic solution?

Answer 20

Causes plasmolysis (cell shrinkage)
(exception = halophiles)

This occurs when the concentration of solutes is higher in the surrounding medium than in the cell.

Question 21

What is the effect of low water activity (A_w) on microbial growth?

Answer 21

Reduces microbial metabolism and growth - causing plasmolysis

This can lead to plasmolysis in bacteria.

Question 22

What is the effect of high water activity (Aw) on microbial growth?

Answer 22

Supports microbial growth, increasing risk of spoilage

Question 23

What are the Aw requirements in bacteria?

Answer 23

Gram +ve = 0.8-0.98 Aw
Gram -ve = 0.97 Aw
Halophiles thrive in low Aw

Question 24

What are each of the chemical requirements for growth for?

Answer 24

carbon = backbone in all organic compounds
N = forms amino acids, DNA/RNA
S= form proteins +some vitamins
P = form DNA,RNA,ATP + phospholipids
Trace elements = used as enzyme cofactors

Question 25

What are obligate aerobes?

Answer 25

Bacteria that require oxygen to live
e.gPseudomonas aeruginosa

An example is Pseudomonas aeruginosa.

Question 26

What are Facultative anaerobes?

Answer 26

Can grow with or without oxygen but prefers aerobic conditions
E.g E.coli

Question 27

What are obligate anaerobes?

Answer 27

Do not tolerate oxygen and are harmed by it
E.gClostridium spp.

Question 28

What is the purpose of selective media in microbiology?

Answer 28

Suppress unwanted microbes and encourage desired microbes

An example is Saboraud’s Agar, which discourages bacterial growth.

Question 29

What is differential media?

Answer 29

Allow distinguishing of colonies of different microbes on the same plate

Question 30

What is an enrichment culture?

Answer 30

Encourages the growth of a desired microbe by increasing very small numbers of an organisms to detectable levels (without suppressing other microbes)

Question 31

What is a pure culture?

Answer 31

Isolating microorganisms to obtain a population of cells arising from a single cell

This is critical for identifying pathogens.

Question 32

Fill in the blank: Most bacteria divide by _______.

Answer 32

binary fission

This process allows for rapid population growth.

Question 33

What is the significance of measuring microbial growth?

Answer 33

To diagnose bacterial infections, assess food safety, and evaluate contamination

This is crucial in clinical and environmental microbiology.

Question 34

What does the term ‘turbidity’ refer to in microbiology?

Answer 34

Measurement of cloudiness/optical density of liquid media

It is linked to the cell mass and can indicate the population size.

Question 35

What is the role of agar in microbiology?

Answer 35

Used as a solidifying agent for culture media

Agar liquefies at 100°C and solidifies at ~40°C.

Question 36

What are the two types of isolating pure culture techniques?

Answer 36

• streaking technique
  *colony formation

Question 37

What are some types of direct measurements of count microbial cells?

Answer 37

*plate count
*filtration
*direct microscopic count

Question 38

What are some types of indirect measurements to count microbial cells?

Answer 38

*turbidity
*metabolic activity
*cell mass - dry weight

Question 39

What is the equation for direct microscopic count technique?

Answer 39

number of bacteria/ml = number of cells counted/ volume of area counted

Question 40

What are the disadvantages to the direct microscopic count?

Answer 40

*difficult to distinguish live/dead bacteria
*often laborious
*often only suitable with high counts