Nutrition 5: Antibiotic resistance

Question 1

What are the 3 classes of antibiotic resistant pathogens which are major threats to humans

Answer 1

1. MRSA- methicillin resistant staphalococcus aureus.
2. Drug resistant gram negative bacteria eg.
   Klebsiella Pneumonia.
3. Drug resistant Mycobacterium tuberculosis
   - leading cause of death from infectious disease

Question 2

What is the relationship between use of antibiotics and Antibiotic resistance

Answer 2

Proportional

Question 3

Where are antibiotics used in the world.

Answer 3

Humans: 1.4 million kg/yr. 1/2 inappropriately prescribed
Animals: 14 million kg in animal food/ yr

Question 4

What are two reasons bacteria develop resistance to AB?

Answer 4

Inherent resistance - based on an inherent structure or functional characteristics of bacteria.

Acquired resistance: where previously susceptible bacteria acquire resistance.

Question 5

How is acquired resistance

Answer 5

Vertical gene transfer

Horizontal gene transfer

Question 6

What is vertical gene transfer

Answer 6

This is transfer of a natural mutation confering resistance from bacterial chromosomes to progeny during DNA replication. This is driven by selective environment. This occurs within the same species

Question 7

What is horizontal gene transfer

Answer 7

Transfer of small bits of DNA between individual bacteria of the same or different species of bacteria.
Through conjugation, transduction and transformation.

Question 8

What is the MRSA- methicillin resistant staphalococcus aureus known for

Answer 8

A strain of Staph that is resistant to the Methicilin which was made to stop the penicillin resistant resistant to penicillin however
resulting in 19000 d/y

Question 9

What is a plasmid

Answer 9

A circular piece of DNA distinct from the chromosome but still passed down to progeny. Usually confer a genetic advantage. eg AB resistance.

Question 10

What are the 3 different kinds of horizontal gene transfer

Answer 10

conjugation, transduction and transformation

Question 11

What is Conjugation gene transfer

Answer 11

• Main mechanism of horizontal gene transfer which
  requires exchange of plasmid through a physical connection between 2 bacteria called pilus.
• Much faster than vertical

Question 12

Transduction gene transfer

Answer 12

Requires bacteriaphage that can infect same or closely related species which transfers the genes. This gene will integrate with the chromosome of recipient cell.

Question 13

Transformation gene transfer

Answer 13

Involves uptake of naked DNA from external environment due to the lysis of the ABR bacteria. This is then integrated into the chromosome/plasmid of recipient cell.

Question 14

What are the 3 principal resistance mechanisms for bacterial ABR genes

Answer 14

1. Efflux (physically remove the AB out of the cell)
2. Enzymatic degradation of AB
3. Enzymatic chemical modification of of AB

Question 15

How does Efflux confer resistance

Answer 15

Bacteria use a variant of a natural pump that will pump the AB out of the cell to prevent AB reaching target in the cell and have enough conc and accumulate in right time frame. Eg Tetracycline.

Question 16

How does Enzymatic degradation/ cleavage confer resistance

Answer 16

The antibiotic is destroyed by chemical modification by an enzyme. Eg. deactivates penicillin by destroying B lactam ring.
The enzyme is secrete in the periplasm so they are destroyed before reach the cell well. Very efficient destroying rate as hydrolyse many molecules per second.
Methicilin was made designed to B lactam cleavage.

Question 17

How does Enzymatic modification confer resistance

Answer 17

Enzyme adds an additional group to antibiotic so its no longer active. Eg. Transferases that add acetyl or phosphoryl group to Chloramphenicol to prevent its binding to the ribosomes.

Question 18

What is other resistance mechanism MRSA

Answer 18

Send out random lipids that the antibiotic daptomycin inserts into (decoys) which decreases the dose before it reaches the membrane.