TOPIC I - Cell Wall Synthesis, Antibiotics, and Human Microbiota

Question 1

Where did antibiotics come from?

Answer 1

nature (ex: soil bacteria, fungi, etc.)

Question 2

Does a bacteriocidal antibiotic kill bacteria?

Answer 2

yes

Question 3

Does a bacteriostatic antibiotic kill bacteria?

Answer 3

no, it inhibits bacterial growth

Question 4

What are the cellular targets for bacteria?

Answer 4

1. cell wall synthesis (inhibited)
2. cell membrane (function disrupted)
3. translation (inhibited)
4. metabolism (inhibited)
5. transcription (inhibited)
6. DNA replication (inhibited)

Question 5

Why did microbes in nature produce antibiotics?

Answer 5

they lived in dense communities with lots of competition –> used antibiotics to kill each other

Question 6

List the antibiotics (learned in class) that inhibit murein (peptidoglycan) synthesis.

Answer 6

1. penicillin G
2. methicillin
3. ampicillin
4. penicillin V
5. vancomycin
6. bactitracin

Question 7

Penicillin G
- natural/semi-synthetic/synthetic/biosynthetic
- narrow spectrum/broad spectrum
- other info:

Answer 7

• natural (from fungi)
• narrow spectrum –> only affects gram + ; cannot penetrate gram -
• penicillin treatment –> osmotic lysis

Question 8

Methicillin
- natural/synthetic/semi-synthetic/biosynthetic
- other info:

Answer 8

• semi-synthetic
• resistant to b-lactamase (an enzyme that some bacteria can produce to be resistant to penicillin)

Question 9

What is b-lactamase?

Answer 9

an enzyme that some bacteria can produce to be resistant to penicillin

Question 10

Ampicillin
- natural/synthetic/semi-synthetic/biosynthetic
- narrow spectrum/broad spectrum
- other info:

Answer 10

• semi-synthetic
• broad spectrum

Question 11

Penicillin V
- natural/synthetic/semi-synthetic/biosynthetic
- narrow spectrum/broad spectrum
- other info:

Answer 11

• semi-synthetic
• acid-resistant
• FRIST orally administered penicillin

Question 12

Vancomycin
- natural/synthetic/semi-synthetic/biosynthetic
- narrow spectrum/broad spectrum
- other info:

Answer 12

• blocks transglycosylase linkage of disaccharides NAG-NAM
• cannot penetrate gram -
• hard to administer
• expensive
• relatively toxic
• LAST RESORT antibiotic

Question 13

What does bacitracin do?

Answer 13

bacitracin blocks the release of NAG-NAM peptide from its lipid carrier

Question 14

Why is the folate biosynthesis pathway a good target for antibiotics?

Answer 14

• folate is an essential vitamin for all organisms
• bacteria rely on their ability to synthesis folate (via folate biosynthesis pathway)
• humans cannot synthesize folate (no folate biosynthesis pathway) –> must ingest folate in their food
• antibiotics that target pathway will not affect human cells

Question 15

Are there different microbiome communities at different body sites?

Answer 15

yes, because of different environments (ex: pH, light, oxygen, etc.)

Question 16

Are microbiomes highly variable between individuals?

Answer 16

yes

Question 17

What are diurnal fluctuations?

Answer 17

refers to how gut microbiota will differ during morning and nighttime due to variations in:
1. body temp
2. nutrient availability
3. concentration of gastrointestinal hormones
4. levels of host-delivered antimicrobial peptides
5. levels of gut mucosal antibodies

Question 18

What are some ways to re-stock beneficial species in the gut microbiome?

Answer 18

1. probiotics (ex: fermented food, yogurt)
2. prebiotics (ex: onions, flaxseed, leeks)
3. fecal transplant

Question 19

Where does antibiotic resistance come from?

Answer 19

1. microbes that are producing antibiotics need to be resistant to it so that they don’t harm themselves
2. large horizontal gene transfer (between the same generation)

Question 20

What are some mechanisms of antibiotic resistance?

Answer 20

1. reduced influx of antibiotics (reduced expression of porins)
2. active efflux of antibiotics
3. antibiotics degradation or modification
4. target modification (ex: reduce binding) or protection
5. bypass the target
6. increased production of target (titration)

Question 21

List the steps in murein (peptidoglycan) synthesis.

Answer 21

1. pentapeptide added to N-acetyl muramic acid
2. peptide-M and N-acetyl glucosamine are linked, creating peptidoglycan subunit
3. peptide-MG is transported (flipped) across cell membrane by a lipid carrier
4. peptide-MG is added to growing polysaccharide chain by transglycosylases
5. peptides are covalently linked by a transpeptidase