L34 Antibiotics, Resistance and Hospital Acquired Infections

Question 1

What are the obvious targets of antibiotics, and why?

Answer 1

Cell wall and ribosomes of bacteria as mammalian cells have no cell wall and they have different types of ribosomes.

Can target specific features of bacterial cells to avoid damaging self.

Question 2

30/50 ribosomes are found in __?__

Answer 2

bacterial cells

Question 3

True or false: Gram positive bacteria are normally anaerobic.

Answer 3

False, they can aerobes or anaerobes. Same for gram negative.

Question 4

Are these gram negative or gram positive?

Staph aureus
Strep pyogenes
C. difficile

Answer 4

Gram positive

Staph aureus and Strep pyogenes are aerobes

C. difficile is an anaerobe

Question 5

Are these gram negative or gram positive?

Pseudomonas
E. coli
Klebsiella pneumoniae
Bacteroides

Answer 5

Gram negative

Pseudomonas, E. coli, and Klebsiella pneumoniae are aerobes.

Bacteroides are anaerobes.

Question 6

Beta-lactams (penicillins, cephalosporins) and glycopeptides (vancomycin, teicoplanin) act on __?__

Answer 6

cell wall of bacteria

Question 7

How do penicillins work on a bacteria cell?

Answer 7

Up to 8 penicillin-

binding proteins on a bacteria, penicillin causes weakening of cell wall and kills the bacteria.

Question 8

What is a beta-lactam ring?

Answer 8

A chemical structure that is found in various beta-lactam antibiotics.

The action of the molecule depends on the groups attached to the ring. The cell wall is a primary target for beta-lactams.

Question 9

Glycopeptides (vancomycin and teicoplanin) interfere with peptidoglycan formation by preventing joining of __?__

Answer 9

N-acetylglucosamine and N-acetylmuramic acid dimers.

Question 10

True or false: Glycopeptides (vancomycin and teicoplanin) are too large to penetrate gram -ve outer membrane, and so are used against gram +ve bacteria - such as streptococci and staphylococci.

Answer 10

True

Question 11

True or false: Glycopeptides (vancomycin and teicoplanin) are bactericidal.

Answer 11

True

Question 12

True or false: There are currently no known glycopeptide-resistant strains of bacteria.

Answer 12

False.

Recent emergence of vancomycin-resistant enterococci (VRE) and staphylococci (VRSA)

Question 13

Daptomycin and colistin act on __?__

Answer 13

Cytoplasmic membrane

Daptomycin: gram +ve
Colistin: gram -ve

Question 14

How do quinolones (ciprofloxacin) work?

Answer 14

Interrupt the action of DNA gyrase, preventing exposed DNA from being resealed. This leads to cell death.

Question 15

How does rifampicin work?

Answer 15

Inhibits RNA polymerase, prevents transcription of DNA.

Question 16

How does metronidazole work?

Answer 16

Binds to bacterial DNA, causing strand breakage

Question 17

What process does trimethoprim affect?

Answer 17

Formation of folic acid in bacteria

Humans get folate from food; bacteria need to synthesise it.

Question 18

True or false: As more antibiotics are prescribed, more strains of resistant bacteria are seen.

Answer 18

True

Question 19

What ways can gene transmission occur in bacteria?

Answer 19

1) Conjugation - plasmids move from one bacteria to another
2) Transduction - bacteriophages moving between bacteria sometimes carry genes
3) Transformation - take up DNA from solution

Question 20

True or false: Antibiotics can cause mutations in genetic information

Answer 20

False

Question 21

True or false: Bacteria can acquire genes encoding enzymes that inactivate antibiotics

Answer 21

True

Examples:

B-lactamases

aminoglycoside-modifying enzymes

Question 22

What mechanisms of antibiotic resistance are known?

Answer 22

• Impermeable cell wall/outer membrane
• Active efflux pumps remove antibiotics from cell
• Altered binding targets (e.g. modified penicillin-binding proteins)
• Bypass of blocked metabolic steps
• Hyperproduction of enzymes
• Inactivation of antibiotics