Bacterial Growth/Nutrition

Question 1

Describe the effects of the streptococcus pyogenes exotoxins SPE A and SPE B.

Answer 1

Streptococcus pyogenes causes strep throat, but can also have other effects:

SPE A—scarlet fever toxin

SPE B—tissue damage associated with toxic shock syndrome and necrotising fasciitis (Flesh eating infection)

Question 2

What are the three major categories of bacterial toxins?

Answer 2

1. ) Damage cellular membranes/matrices
2. ) Inhibit protein synthesis
3. ) Activate secondary messenger pathways

Question 3

Describe the function of the Type III secretory apparatus.

Answer 3

Looks like a needle—toxins go through the needle and are injected outside of the cell or directly into the host cell

Question 4

Some bacterial pathogens can enter the cell using effector proteins and replicate intracellularly. Why is this beneficial?

Answer 4

Ample nutrients for growth and protection from the immune system.

Remember the bacterial cell wants to survive and have progeny, it is not there just to kill the host. Making exotoxins is not the primary goal.

Question 5

Why is the pure culture technique so important?

Answer 5

Growing the bacteria can tell us a lot of key identifying characteristics. As we grow the bacteria, the purer the sample, the more reliable the results.

Additionally, if the bacterial sample is grown in the wrong conditions, it could lead to unreliable results

Question 6

List three factors that affect the growth rate of batería.

Answer 6

1. ) Medium composition
2. ) Temperature
3. ) Oxygen levels

Question 7

What are the four stages in the growth cycle?

Answer 7

Lag phase (getting used to the environment)
Exponential phase (grows exponentially as long as nutrients are present)
Stationary phase (equal growing/dying levels)
Death (nutrients run out)

Question 8

How is DNA replication inhibited in bacteria?

Answer 8

Fluorquinolone inhibits DNA replication by binding to two enzyme (DNA girase and Topoisomerase IV). These are different enough from human cells that the fluorquinolone causes no inhibition in human cells.

Question 9

How is protein synthesis inhibited in bacterial cells.

Answer 9

Erythromycin, tetracycline, streptomycin, spectinomycin all inhibit ribosome function. Bacterial ribosomes are different from human ribosomes—the drugs do not inhibit our cells.

Question 10

How can we use the peptidoglycan layer to attack bacteria?

Answer 10

There are three steps in peptidoglycan synthesis: synthesis, translocation, and incorporation. These can be targeted by antibiotics. Since we don’t have peptidoglycan layers in our cells, the antibiotics will have no effect on our cells.

Question 11

Describe penicillin binding proteins

Answer 11

Enzymes involved in cell wall metabolism

Have a low affinity for ß-lactan antibiotics (penicillin, ampicillin, cefotaxime)

Are a major contributor to ß-lactam resistance strains of S. Pnuemoniae, s. Aureus, and other gram + cocci

Mutations in these proteins leads to resistance, renders antibiotics useless

Question 12

Explain the relationship between cefotaxime (antibiotic) and PBP (penicillin binding protein.

Answer 12

Cefotaxime binds to a pocket in the S. Pneumoniae PBP, inhibiting the final step of cell wall synthesis in the bacteria.

If there were to be a mutation in this pocket and the cefotaxime couldn’t bind, the drug would become ineffective.

Question 13

What are the four major targets of antibiotics?

Answer 13

1. ) Peptidoglycan synthesis
2. ) Cell membrane
3. ) RNA polymerase
4. ) Ribosome inhibitors

Question 14

What are three reasons why the metabolism of bacteria is relevant?

Answer 14

1. ) Defines the preferred environment
2. ) Facilitates identification
3. ) Revelas methods for killing or suppressing bacteria

Question 15

What is the role of siderophores in bacterial thriving?

Answer 15

Siderophore are small molecules produces by microbes that are excreted and bind with high affinity to Fe. The bacteria needs Fe to grow, and the siderophores bring Fe into the cell for growth

There is a constant war for host nutrients. If the bacteria can win, they enter the exponential phase.

Question 16

Where are the proteins for fermentation and respiration located in a bacterial cell?

Answer 16

In the membrane. Antibiotics that interfere with the membrane will disrupt these processes.

Question 17

How are the products of metabolism used identification?

Answer 17

Each organism produces different products of metabolism that help us identify them.

Example: Catalase is produced by aerobically active bacteria (H2O2 is a toxic byproduct of respiration and can be remediate by catalase enzymes)

Question 18

What are two examples of generic stress responses of bacteria (to starvation and heat)?

Answer 18

Starvation: Spore formation

Heat: Synthesis of Heat Shock protein

Question 19

Give two examples of pathogenesis-specific stress responses.

Answer 19

1. ) Expression of bacterial toxins and nutrient acquiring systems (ex: haemolysins and siderophores)
2. ) Pili (adherence to host)

Question 20

Explain how host localization helps with the need for precise control of gene expression for pathogenesis

Answer 20

During infections, pathogens must express certain genes in certain locations in the host, and other genes in other locations

Example: Host-environment restriction of gene expression: S. enterica

Question 21

Explain how the timing of gene expression helps with precise control of gene expression in pathogenesis.

Answer 21

Pathogens must also be able to control the timing of gene expression, to ensure that virulence factors are made at the correct times and in the proper order.

Example: Temporally controlled gene expression: V. Cholerae

Question 22

Explain how SPIs (salmonella pathogenicity islands) influence infection.

Answer 22

Specific SPIs are needed to infect specific organs

SPI 1= small intestines
SPI 2= spleen, liver
SPI 3= spleen, liver
SPI 4 = Spleen, liver

Which SPI is expressed determines the site of infection

Question 23

Explain the three steps of Vibrio cholerae pathogenesis

Answer 23

1. ) Lumen entry (0-1 hours, asymptomatic)
2. ) Pili attachment (2-3 hours, still likely asymptomatic)
3. ) Establishment of biofilm = cholera toxin production (>4 hours)

Question 24

What kind of structure does gene regulation have?

Answer 24

Hierarchical. The progression of gene expression has to happen in a timely manner, hierarchically, or else the bacteria will not survive.