Bacterial Growth Lecture Sep 6

Question 1

How do bacteria multiply?

WHat are the 4 general steps?

Answer 1

They multiply by binary fission

1. Replication of DNA
2. Polar separation of daughter chromosomes
3. Generation of the cross-wall
4. Separation

Question 2

What is a bacteria’s generation time?

Answer 2

The time for one cell to beomc two

or

The amount of time required for the number of cells in a culture to double

Doubling time = generation time

Question 3

How are cell numbers generally measured?

Answer 3

They’re usually measured by cell concentration or biomas

Question 4

How is a growth curve generated for a bacteria?

Answer 4

1. A saturated broth culture is used to inoculate fresh media
2. Bacterial counts are taken at different time points and plotted as cell number vs time

Question 5

What happens in the lag phase of the growth curve?

What happens in log phase of the growth curve?

Answer 5

During the lag phase the bacteria adapt to the new nutrient-rich environment and synthesize the appropriate proteins

During the log phase the bacteria are doubling ever generation time (this is also called the logarithmic or exponential growth phase)

Question 6

What will have a steeper log phase on a growth curve:

a bacteria growing in the blood, or a bacteria growing in an abscess?

Answer 6

Bacteria growing in an abscess will have a flatter log phase line because abscesses are less vascularized and have fewer nutrients for the bacteria to use.

The log phas elien will be steeper for bacteria in the blood because nutrients are present and the bacteria doesn’t need to use any of its energy to make its own nutrients

Question 7

What is happening in the stationary phase of the growth curve?

What’s happening in the death phase of the growth curve?

Answer 7

During the stationary phase the nutrients are exhuasted and toxic products being to build up. The bacteria remain at a relatively constant number (this is the plateau on the growth curve)

During the death phase, bacteria begin to die because of toxicity. Not all bacteria have a death phase.

Question 8

How does one determine bacterial concentration?

Answer 8

1. Take a liquid sample
2. Make a 10-fold dilution of the culture
3. Spread a known volume on an agar plate
4. Allow colonies to grow
5. Count the number of colonies
6. Each colony represents one bacterium in the original sample
7. Calculate the original concentration

Question 9

What qualifier is necessary when interpreting results of a bacterial concentration by serial dilutions and CFU growth?

Answer 9

Such a method will only represent VIABLE bacteria

This is important in the case of gram negative bacteria whose pathogenicity relies mainly on the presence of lipid A endotoxin. This can be present and causing symptoms even if the bacteria is already dead. So symptoms from such an infection would be result in a culture with bacteria growth.

Question 10

Why are the dilution steps necessary in the serial dilution/CFU method of determining bacterial concentration?

Answer 10

Dilution allows you to actually count the colonies. If you plated the original solution, there would be so many that they’d grow together and you wouldn’t be able to count them.

Question 11

What are the requirements for growth?

Answer 11

1. All the elements for organic matter (especially a carbon source)
2. Ions for energy generation, catalysis, and osmotic maintenance

Question 12

What does it mean to say that bacteria have inducible genes?

Answer 12

It means that the bacteria will only produce certain gene product if it senses that the environment requires such gene products.

For example, if you have a bacteria that is capable of synthesizing all its organic compounds from carbon and nitrogen and oxygen, then putting the bacteria into a culture with plenty of those compounds around will make the bacteria not produce the enzymes it needs to make the compounds–the compounds are already there, so why waste the energy?

Question 13

What are the three possible energy sources (or rather methods of developing energy) in bacteria?

Answer 13

1. Fermentation: the formation of ATP not coupled to electron transfer
2. Respiration: the formation fo ATP via oxidative phosphorylation wherin ATP is formed during electron transfer
3. Photosynthesis: ATP is formed via the reduction of an oxidant via light energy. Similar to respiration.

Question 14

Which would a facultative anaerobe prefer: fermentation or respiration?

Answer 14

They would prefer respiration because you develop so much more ATP when O2 is the electron acceptor.

Question 15

What are some compounds other than O2 that some bacteria use as the final electron acceptor?

Answer 15

NO3, SO4

Question 16

Why are fermentation products useful in bacterial identification?

What bacteria produce lactic acid from fermentation?

What bacteria produce ethanol and CO2?

Propionic acid, acetic acid, CO2 and H2?

Butyric acid, butanol, acetone, isopropyl alcohol, CO2?

Ethanol, lactic acid, succinic acid, acetic acid, Co2, H2?

Ethanol, lactic acid, formic acid, butanediol, acetone, CO2, H2?

Answer 16

You can identify the bacteria based on the fermentation product they produce.

1. Streptococcus; Lactobacillus, Bacillus
2. Saccharomyces (yeast)
3. Propionibacterium
4. CLostridium
5. Escherichia, Salmonella
6. Enterobacter

Question 17

WHat are the 3 classifications of bacteria based on nutritional requirements?

Answer 17

Heterotroph - requires pre-formed organic compounds like sugars, amino acids, and vitamins

Autotroph - can synthesize everything it needs from inorganic compounds like CO2

Hypotroph–is an obligate intracellular pathogen requiring the host to provide organic compounds (in this way it may also be called an intracellular heterotroph)

THe majority of medically important bacteria are heterotrophs

Question 18

How do bacteria take up their nutrients from the environment?

Through what 3 basic ways?

Answer 18

Diffusion through the cytoplasmic membrane occurs with the help of specific carrier proteins called permeases

1. carrier mediated diffusion (facilitated diffusion)
2. Phosphorylation-linked transport
3. Active transport

Question 19

Describe carrier mediated diffusion (facilitated diffusion).

Answer 19

Nutrients travel across a concentration gradient, from highest to lowest concentration. e.g. if the concentration of glycerol inside the organism drops, the cell will take up more glycerol

This is concentration dependent

It is NOT energy dependent

Question 20

Describe phorphorylation-linked transport (group translocation)

Answer 20

This IS an energy dependent process, also known as group translocation.

Certain sugars are taken up this way

The sugars are co-transported with a carrier in the membrane of the cells and chemically phosphorylated in the process.

Question 21

Describe active transport

Answer 21

This IS an energy-dependent process.

It requires the generation of a proton-motive force.

Protons are pumped out of the cell, creating a flux of protons in and out of the organism

Molecules are coupled to the uptake of protons, making the overall energetics favorable.

This requires a symport for the uptake of protons and the nutrient.

Question 22

What are the 5 basic types of bacteria classified by their oxygen requirements?

Answer 22

1. Oligate aerobes
2. obligate anaerobes
3. facultative anaeroves
4. microaerophiles
5. aerotolerant anaerobes

Question 23

What is the O2 requirement of oglibate aerobes?

Answer 23

They MUST have O2 for growth

Question 24

What is the O2 requirement of an oligate anaerobe?

Answer 24

They will be killed in the present of O2 because they cannot reduce the ROS produced during the metabolism of O2

Question 25

What are the O2 requirements of facultative anaerobes?

Answer 25

They can grow with or without O2

Question 26

What are the O2 requirements of microaerophiles?

Answer 26

They must grow at low concentrations of O2 (less than 20%)

Question 27

What are the O2 requirements for an aerotolerant anaerobe?

Answer 27

Similar to facultative anaerobes, but unlike most facultative anaerobes, they actually prefer anaerobic growth

Question 28

What two compounds must a bacteria have in order to be an aerobe (obligate or facultative?)

Answer 28

They need to have superoxide dismutase to reduces osygen radicals to hydrogen peroxide.

THey also need either catalase or peroxidase to further break down the peroxide to water.

Question 29

In a tube where oxygen concentration is high near the top and nonexistent at the bottom, where will the following species grow:

1. Obligate aerobe?
2. Microaerophile?
3. Obligate anerobe?

Facultative anaerobe?

Answer 29

1. at the top
2. somewhere in the middle
3. down at the bottom
4. through the whole tube

Question 30

What are the 3 classifications of bacteria based on optimal growth temperature?

Answer 30

Psychrophiles: grow best in the range of 0-20 degrees C

Mesophiles: grow best in 20-45 degrees C

Thermophiles: grow best in the range of 45-90 degrees C

Question 31

What is added to liquid media to make solid media?

What does it mean for a media to be a defined media?

Answer 31

They add agar to the broth recipe (usually about 15% to make agar plates)

Defined media is made with chemicals at known concentrations

Question 32

What is the difference between differential media and selective media?

Answer 32

Differential media supplies mutrients and indicators for VISUAL DETERMINATION of which organisms are present.

Selective media selects AGAINST the growth of particular bacteria by the addition of dyes, acid/base, salts or antibiotics

Question 33

What is an example of a media that is both selective and differential?

Answer 33

MacConkey agar

bile salts and crystal violet inhibit the growth of gram positive (selective) and has lactose plus a pH indicator to indicate the fermentation of lactose (differential)