Antimicrobial resistance

Question 1

Which resistance mechanism to erythromycin that involves the alteration of its target site

Answer 1

Innate resistance

Question 2

Describe a resistance mechanism to an antibiotic that involves modification of the antibiotic to a less active form.

Answer 2

drug inactivation by modifying antibacterial agent
Aminoglycosides can be phosphorylated, acetylated & adenylated
E.g. Chloramphenicol is acetylated (acyl group added) by chloramphenicol acetyltransferase ≠ bind to ribosomes (bc not complementary to site on ribosome)

Question 3

How does penicillinase protect a microbe from penicillin?

Answer 3

penicillinase breaks the B-lactam ring structure of antibact. = drug inactivated

Question 4

Give 2 factors that may have contributed to the emergence of antibiotic resistant bacteria (7)

Answer 4

• Selective pressures of antibiotics
• Overprescription
• (Over)use of antibiotics in food production
• immunocompromised patients - require antibiotic treat.
• invasive surgery - require antibiotic treatment
• Mobility of human population: introduce micro-o to places not initially there
• Bact. has many transfer mechanisms

Question 5

Describe role of Multidrug resistance (MDR) transporters

Answer 5

pump a wide variety of compounds (not structurally similar) out as it enters the cell via:

• 2º transporters driven by proton (H+) or Na motive force (which come in while drug goes out)
• ATP- binding cassette (ABC) 1º transported through hydrolysis of ATP (=> energy)

Question 6

Define transformation

Answer 6

Incorporate naked DNA into a competent recipient cell

Question 7

Define transduction

Answer 7

DNA transferred as part of a virus

Question 8

What’s the principle of generalised transduction

Answer 8

1. phage infects cell
2. function of cell is altered to make multiple copies of viral cell
3. During packaging, a portion of bact. DNA is picked up (w or w/out viral DNA) => transduced phage
4. Phage infects bact. cell inserting DNA (may code for resistance) => transduced cell

Question 9

What is the role of F-pilus (TRApilin) during conjugation?

Answer 9

F (fertility) pilus (GN bact.) extends to neighbouring bact. cells & acts as a passageway for transferring DNA from donor to recipient cell

Question 10

Define conjugation

Answer 10

Transfer of genetic material from donor cell to recipient cell via cell-to-cell contact

Question 11

What is an R-factor?

Answer 11

resistance factor in a plasmid that codes for antibiotic resistance

Question 12

What is the main distinction b/w insertion sequence (IS) elements & transposons?

Answer 12

• IS: consist of genes for transposition (move) in b/w inverted repeats (transposase enzyme > cut DNA)
• Transposons: consist of anti-biotic resistant gene in b/w inverted repeats (> can be cut & moved to other species)

Question 13

What’s the diff. b/w innate & acquired resistance

Answer 13

• Innate: non-specific immunity that’s naturally inherited

- Acquired: successful mutation OR gene transfer from another OR both

Question 14

*List the types of innate immunity & e.g. (4)

Answer 14

• 1a. alter target site: little/no affinity of ribosomes to drug e.g. methylation of A => conformation change = reduce affinity for macrolides
  1b. bypass mechanisms e.g. use alternative enzymes to synthesis folic acid w/out inhibited by sulphonamides
  2. Destroy antibacterial agent: B-lactamase; amidase > remove R-group in penicillins

Question 15

What’s the innate resistance of Pseudomonas aueruginosa?

Answer 15

• B-latamases
• impermeable outer membrane (can control pore size)
• efflux pumps
• biofilm

Question 16

Describe a resistance mechanism to an antibiotic that involves reduction of intracellular lvls of antibiotics

Answer 16

• can’t enter cell via outer membrane (penicillin G) or C.wall (erythromycin)
• alter permeability
• efflux pumps: Specific DS or MDR transporters e.g tetracycline pump