Bacteria

Question 1

Describe the differences between prokaryotic and eukaryotic cells

Answer 1

Eukaryotes

• DNA in nucleus
• Membrane-bound organelles
• 80s ribosomes

Prokaryotes

• No nucleus
• Organelles not membrane-bound
• 70s ribosomes
• Most bacteria have a peptidoglycan cell wall

Question 2

List some drug targets for antibiotics

Answer 2

• Cell wall
• Cell membrane
• Nucleic acid synthesis
• Protein synthesis

Question 3

Why is the cell wall a good target for antibiotics?

Answer 3

Because it contains a component unique to bacteria (peptidoglycan)

Question 4

Example and mode of action of penicillin

Answer 4

• Pencillin (ß-lactam) inhibits enzymes e.g. traspeptidase involved in forming cross-links between peptidoglycans
• Also promote autolysin activity

Question 5

Example of an antiobiotic that acts on bacterial cell walls

Answer 5

Penicillin / β-lactam

Question 6

Why is the cell membrane a good target for antibiotics?

Answer 6

Disrupting the functional integrity of the cell membrane leads to escape of macromolecules and ions from bacteria –> cell death

Question 7

What are the disadvantages of using an antibiotic that targets the cell membrane?

Answer 7

• High similarity between animal and bacterial cell membranes means antibiotic is also toxic to body cells
• Potential for surrounding tissue damage, side effects
• Should be used as a last resort

Question 8

Example of antibiotic that targets cell membrane

Answer 8

Colistin

Question 9

Bateriostatic

Answer 9

prevents multiplication of bacteria without destroying them outright

Question 10

Why is nucleic acid synthesis a good target for antibiotics?

Answer 10

Organisation and replication of bacterial DNA and RNA different to eukaryotes

Question 11

Give an example and mode of action of antiobitics that act of nucleic acid synthesis

Answer 11

• Quinolones
• Act on DNA gyrase, which separates DNA strands during bacterial replication

Question 12

Why is protein synthesis a good target for antibiotics?

Answer 12

There are differences between eukaryotic (80s) and prokaryotic (70s) ribosome structure

Question 13

Give the example and mode of action of an antibiotic that targets protein synthesis

Answer 13

• Tetracyline
• Blocks tRNA molecule attachment site on 30s subunit

Question 14

Virulence factor

Answer 14

molecule that allows bacteria to adhere, invade, evade host defence, cause tissue damage, replicate or persist in the host.

Question 15

Virulence genes

Answer 15

Genes encoding a virulence factor

Question 16

How have virulence genes evolved?

Answer 16

• Horizontal gene transfer has enabled rapid evolution
  
  • Mobile elements such as plasmids, transposons, phages

Question 17

PAMP

Answer 17

Pathogen associated molecular patterns: specific components expressed by the pathogen and recognised by the host as ‘danger signals’.

Question 18

PRR

Answer 18

Pattern recognition receptor: specific receptor expressed by the host that recognise PAMPs.

Question 19

TLR

Answer 19

Toll-like receptors: transmembrane receptors on a wide range of cels types, and that have a wide range of roles.

e.g. TLR4, important for the recognition of LPS

Question 20

How do TLRs differentiate between pathogenic and commensal bacteria

Answer 20

Number of strategies - main one is location of TLRs

• TLRs expressed on the basal surface of epithelial cells, but not on apical surface, that is in contact with gut lumen
• Thus commensal bacteria are tolerated by only in the right place
• If these bacteria are found elsewere, an inflammatory response will be stimulated

Question 21

Septicaemia

Answer 21

presence of viable bacteria in the bloostream. Does not always, but can develop into sepsis.

Question 22

SIRS

Answer 22

Systemic inflammatory response syndrome: systemic respose to an array of severe clinical insults.

Question 23

Shock

Answer 23

SIRS induced hypotension unmanageable by fluid resuscitation, in association with hypoperfusion, leading to ischemia.

Question 24

Sepsis

Answer 24

SIRS due to infection

Question 25

MODS

Answer 25

Multiorgan dysfunction syndrome: altered organ function in an acutely ill patient requiring intervention to maintain homeostasis.

Question 26

Characteristics of gram negative bacteria

Answer 26

• Double membrane
• Outer membrane is immune reactive