CSIM 1.43 Development of Antibiotic Resistance

Question 1

What is the definition of antibiotic?

Answer 1

Any substance produced by a microorganism which inhibits growth of other microorganisms

Question 2

Which type of bacteria is more susceptible to beta-lactam containing antibiotics?

Answer 2

Gram-positive bacteria

Question 3

What does penicillin bind to? What is the normal function of this

Answer 3

Penicillin binding protein
• Normally cross links the chains of the cell wall forming peptidoglycan
• Penicillin binds to the active site of this protein
• Therefore the cross-linking stops forming
• The cell wall size is now fixed, but the bacterium still tries to grow
• The osmotic and cell contents pressure exceeds what the cell wall is capable of containing and the cell membrane herneates from the cell wall
• The cell wall is shed, forming a spheroplast
• There is now no protection from osmotic pressure, so the cell eventually bursts - death by osmosis

IMG 113

Question 4

In what ways can antibiotic resistance come about?

Answer 4

• Bacterium can chemically modify the antibiotic
  
  • The bacterium can physically remove the antibiotic from the cell (in antibiotics which require entry)
  • Modifying the target site so that it is not recognised by the antibiotic
  • Metabolic bypass (multiple pathways for a particular reaction)

Question 5

What misuse of antibiotics can lead to antibiotic resistance?

Answer 5

• Prophylactic use
  
  • Incorrect prescribing
  • Not finishing a course

Question 6

What enzyme can break down penicillin?

What does it break penicillin down into?

Answer 6

Beta-lactamase

Penicilloic acid

Question 7

What are the two mechanisms of genetic change?

Answer 7

Vertical gene transfer
• Mutation and evolution

Horizontal gene transfer
• Same generation transfer of genes

Question 8

What are the three mechanisms of horizontal gene transfer?

Answer 8

• Transformation
  
  • Transduction
  • Conjugation

Question 9

Describe transformation with regard to horizontal gene transfer

Answer 9

Uptake of naked NDA from the environment and incorporation into recipient in a heritable form

• Free DNA binds to DNA binding proteins in the cell membranes of the bacterium
• This protein breaks this down into a single-strand, which is fed inside of the cell
• Competence specific proteins binds to this single-stranded DNA and guides the DNA
• The DNA is fed into the chromosome of the cell
• If a gene is present, it is expressed, if this gene increases virulence, the cell will now have a survival advantage

Question 10

Describe transduction with regard to horizontal gene transfer

Answer 10

Transfer of bacterial DNA via a bacteriophage - can be GENERALISED or SPECIALISED
• The bacteriophage picks up some host DNA during its assembly
• This is delivered to a new cell when the bacteriophage is released

Question 11

Describe conjugation with regard to horizontal gene transfer

Answer 11

A donor cell makes contact with a recipient cell and DNA is transferred
• The ‘male donor’ status is determined by the presence of an extrachromosomal length of double stranded DNA called a ‘transmissible plasmid’
• Direct contact occurs, instigated by ‘conjugation apparatus’
• Sex pili of donor cell binds to recipient receptor
• A pore forms between the two cells cytoplasms
• The plasmid is cleaved into two single stranded lengths of DNA
• One enters the female cell, the other remains in the male cell
• The single strand is replicated into a double strand in both cells
• The cells detach, the recipient becomes a donor and becomes male due to plasmid presence

IMG 114

Question 12

What type of bacteria is most likely to undergo conjugation?

Answer 12

Gram-negative

although plasmids can transfer between different species

Question 13

What are the three types of plasmid?

Answer 13

1) R-plasmids 0 genes for antibiotic resistance
2) Virulence plasmid - genes which effect virulence
3) Metabolic plasmids - genes that affect metabolism