L13 Antibiotics

Question 1

What is an antibiotic?

Answer 1

A compound that inhibits the growth of or kills bacteria, either derived from natural sources or synthesised.

Question 2

What is the difference between an antibiotic and an antimicrobial?

Answer 2

• Antibiotic: Specifically targets bacteria.
• Antimicrobial: Targets a broader range of microbes, including viruses, fungi, and protozoa.

Question 3

What is selective toxicity in antibiotics?

Answer 3

The ability of an antibiotic to target bacteria specifically without harming the host.

Question 4

What are the two main uses of antibiotics?

Answer 4

• Treatment of bacterial infections.
• Prophylaxis to prevent bacterial infections (e.g., surgery or outbreaks).

Question 6

How do antibiotics benefit society?

Answer 6

They reduce mortality, prevent disease spread, and enable complex medical procedures like organ transplants and chemotherapy.

Question 7

Name five bacterial targets of antibiotics.

Answer 7

• Cell wall biosynthesis.
• Cell membrane integrity.
• DNA and RNA synthesis.
• Protein synthesis.
• Metabolic pathways.

Question 8

What is the Minimum Inhibitory Concentration (MIC)?

Answer 8

The lowest concentration of an antibiotic that inhibits bacterial growth.

Question 9

What is a breakpoint concentration?

Answer 9

The antibiotic concentration below which bacteria are considered susceptible to the drug.

Question 10

What are the two main ways bacteria develop resistance?

Answer 10

• Mutations in chromosomal genes.
• Acquisition of foreign DNA (e.g., plasmids).

Question 11

What is the Mutant Prevention Concentration (MPC)?

Answer 11

The antibiotic concentration that prevents the growth of resistant mutants.

Question 12

What are beta-lactams, and how do they work?

Answer 12

A class of antibiotics that inhibit bacterial cell wall synthesis (e.g., penicillins, cephalosporins).

Question 13

Name an example of a fluoroquinolone and its target.

Answer 13

Ciprofloxacin, which targets DNA synthesis.

Question 14

What is the main use of aminoglycosides like gentamicin?

Answer 14

Treating severe infections caused by gram-negative bacteria.

Question 15

What does pharmacokinetics (PK) study in antibiotics?

Answer 15

How the body absorbs, distributes, metabolises, and eliminates the drug.

Question 16

What does pharmacodynamics (PD) study?

Answer 16

The effects of the drug on the bacteria, including potency and time-dependent or concentration-dependent killing.

Question 17

How do quinolones differ in their distribution compared to beta-lactams?

Answer 17

Quinolones penetrate more effectively into tissues like sputum and alveolar macrophages.

Question 18

How do gram-positive bacteria differ from gram-negative bacteria structurally?

Answer 18

• Gram-positive: Thick peptidoglycan layer, no outer membrane.
• Gram-negative: Thin peptidoglycan layer, outer membrane present.

Question 19

Name two gram-positive and two gram-negative pathogens.

Answer 19

• Gram-positive: Staphylococcus aureus, Streptococcus pneumoniae.
• Gram-negative: Escherichia coli, Pseudomonas aeruginosa.

Question 20

What strategies are being pursued to combat resistance?

Answer 20

• Modifications to existing antibiotic classes.
• Development of combination therapies.
• Targeting gram-positive pathogens.

Question 21

What is synergy in antibiotic combinations?

Answer 21

When the combined effect of two antibiotics is greater than their effects individually.

Question 22

Why is combination therapy sometimes necessary?

Answer 22

To prevent resistance, broaden spectrum, or enhance efficacy.

Question 23

What colour do gram-positive bacteria stain, and why?

Answer 23

Purple, because the thick peptidoglycan layer retains the crystal violet stain during the Gram-staining process.

Question 24

What colour do gram-negative bacteria stain, and why?

Answer 24

Pink or red, because the thin peptidoglycan layer does not retain the crystal violet stain and takes up the counterstain (safranin).

Question 25

What is the role of the outer membrane in gram-negative bacteria?

Answer 25

• Acts as a barrier to many antibiotics.
• Contains lipopolysaccharides (LPS) which can trigger strong immune responses in humans.

Question 26

Why are gram-negative bacteria often more resistant to antibiotics?

Answer 26

• The outer membrane acts as an additional barrier to antibiotic entry.
• Many produce beta-lactamases, which degrade beta-lactam antibiotics.

Question 27

Which antibiotics are most effective against gram-positive bacteria?

Answer 27

• Penicillin.
• Vancomycin.
• Clindamycin.
• Macrolides (e.g., erythromycin, azithromycin).

Question 28

Which antibiotics are most effective against gram-negative bacteria?

Answer 28

• Aminoglycosides (e.g., gentamicin).
• Fluoroquinolones (e.g., ciprofloxacin).
• Carbapenems (e.g., meropenem).
• Third-generation cephalosporins (e.g., ceftriaxone).

Question 29

Why are beta-lactam antibiotics sometimes combined with beta-lactamase inhibitors?

Answer 29

To overcome resistance in beta-lactamase-producing bacteria (e.g., augmentin = amoxicillin + clavulanic acid).

Question 30

What are the steps of the Gram-staining process?

Answer 30

1. Crystal violet stain: Both gram-positive and gram-negative bacteria are stained purple.
   Iodine treatment: Forms a complex with the crystal violet.
2. Alcohol/acetone wash:
   - Gram-positive: Retains the purple stain.
   - Gram-negative: Loses the stain.
3. Counterstain (safranin):
   - Gram-positive: Remains purple.
   - Gram-negative: Stains pink/red.

Question 31

What is the purpose of iodine in Gram staining?

Answer 31

It binds to the crystal violet, forming a complex that is harder to wash out.

Question 32

Why do gram-negative bacteria lose the crystal violet stain during alcohol washing?

Answer 32

The thinner peptidoglycan layer and the presence of an outer membrane allow the crystal violet-iodine complex to be washed out.

Question 33

Which types of infections are commonly caused by gram-positive bacteria?

Answer 33

Skin infections (e.g., cellulitis by Staphylococcus aureus).
Respiratory infections (e.g., pneumonia by Streptococcus pneumoniae).
Endocarditis (infection of the inner lining of the heart)

Question 34

How do gram-positive bacteria develop resistance to antibiotics?

Answer 34

• Modification of penicillin-binding proteins (e.g., MRSA).
• Efflux pumps to expel antibiotics.
• Enzymatic inactivation (e.g., beta-lactamase production).

Question 35

How do gram-negative bacteria develop resistance to antibiotics?

Answer 35

• Outer membrane prevents drug entry.
• Production of extended-spectrum beta-lactamases (ESBLs).
• Efflux pumps and porin mutations reduce antibiotic uptake.