Antibiotics - Resistance

Question 1

What are the 2 main types of resistance to antibiotics?

Answer 1

Inherent resistance (bacteria lack specific pathway/target that the drug interacts with)

Acquired resistance (bacteria gain genetic material coding for resistance)

Question 2

What are the 4 main mechanisms of antibiotic resistance?

Give an example of each.

Answer 2

Bacteria enzymes which break down drug (e.g. beta lactamases)
Antibiotic target is changed (e.g. 30S ribosome mutations)
Downregulation of porins so that antibiotic cannot enter the cell
Bacteria actively pump drugs out of the cell in exchange for H+ (e.g. multidrug efflux pumps in pseudomonas)

Question 3

What are the 2 main types of gene transfer in bacteria?

Answer 3

Vertical (genetic information passed from a parent cell to its daughter cells)

Horizontal (genetic info is transferred via means other than production)

Question 4

What are the 4 main methods in which bacteria acquire resistance?

Answer 4

Spontaneous chromosomal mutation
Conjugation
Transduction
Transformation

Question 5

Briefly describe the process of conjugation. (2)

Answer 5

1. Cell to cell contact is needed so that cells can transfer plasmids/integrons/transposons containing DNA
2. This can transfer bacterial mutations encoding for resistance between different species

Question 6

Briefly describe the process of transduction. (1)

Answer 6

1. Bacteriophages transfer bacterial DNA between bacteria

Question 7

Briefly describe the process of transformation. (3)

Answer 7

1. Cell wall of dead bacteria is broken down, releasing contents (including naked DNA)
2. Other bacteria can then pick up loose DNA and incorporate it into their own chromosomes
3. Only some bacteria can do this, e.g.
   a. Strep. pneumoniae

Question 8

List 3 non-genetic mechanisms of antibiotic resistance.

Give some examples of each.

Answer 8

Protected environments (e.g. abscesses, appendix)
Resting stage
Presence of a foreign body (e.g. biofilm production)

Question 9

Describe the mechanism of action in MRSA.

Answer 9

1. MecA gene is mutated, causing a conformational change in the penicillin binding protein
   a. This causes a lower affinity for methicillin
2. Therefore, methicillin can no longer bind to the penicillin binding protein on the cell wall
   a. But, PBPs can still bind to each other
   b. Therefore crosslinking still occurs, and the cell wall is intact

Question 10

Which antibiotics are coliforms often resistant to? (4)

Give an example of each type of antibiotic.

Answer 10

Penicillins (e.g. amoxicillin)
Quinolones (e.g. ciprofloxacin)
Cephalosporins (e.g. ceftriaxone)
Aminoglycosides (e.g. gentamicin)

Question 11

List 4 mechanisms of resistance in coliforms.

Answer 11

Beta lactamases

Extended spectrum beta lactamases (resistance to penicillins AND cephalosporins)

Carbapenemases (e.g. NMD1)

Loss of porins

Question 12

Give 1 example of a carbapenemase found in coliforms.

Answer 12

NDM1