Bacterial Genetics and Antibiotic Resistance

Question 1

What class of antibiotics inhibit DNA gyrase and give an example of one?

Answer 1

Fluoroquinolones
- ciprofloxacin
(Also novobiocin but this is not a fluoroquinolone)

Question 2

Through which mechanisms can bacteria become resistant to antibiotics?

Answer 2

• The part of the bacteria which the antibiotic targets becomes mutated
• The bacteria breaks down the antibiotic
• The antiobiotic breaks down the antibiotic
• The antibiotic becomes effluxed

Question 3

Give an example of an antibiotic which has become less effective due to mutation of the drug target as a mechanism of resistance

Answer 3

Rifampicin

- A single nucleotide/amino-change in rpoB alters affinity for drug without affecting function

Question 4

What does Rifampacin work against and by what mechanism?

Answer 4

Used in the traetment of TB (in combination with other drugs and used in prophylaxis)
- Inhibits RNA polymerase

Question 5

What other drugs are vulnerable to resistance due to target site mutations (other than rifampacin)?

Answer 5

• Streptomycin

- Ciprofloxacin

Question 6

Give an example of a class of drugs which is vulnerable to resistance through bacteria being able to modify them?

Answer 6

Aminoglycosides (e.g streptomycin)

- The bacteria add small molecules to the drug to prevent it binding to the ribosome

Question 7

Give examples of antibiotics which can be evaded by efflux

Answer 7

• Tetracycline
• Chloramphenicol
• Fluoroquinolones
• Beta-lactams
  Efflux mechanisms may give resistance to multiple antibiotics

Question 8

How may bacteria develop resistance through an efflux pump?

Answer 8

• May up-regulate existing pump (by mutation - may arise during treatment)
• Bacteria may acquire genes for new pump

Question 9

How much more DNA do humans have in comparison to bacteria?

Answer 9

About 1000 times more

Question 10

How much less genes do bacteria have in comparison with humans?

Answer 10

Only around 10 times less

Question 11

How do bacterial chromosomes compare to human?

Answer 11

• Bacterial chromosomes are haploid and circular (human are diploid and linear)

Question 12

What is the bridge called that is used to transfer plasmids from one bacteria to another?

Answer 12

Pilus

Question 13

What is an insertion sequence?

Answer 13

• Elements of DNA which are capable of excision and inserion into new locations in chromosome or plasmid
• Most basic transposable element
• Sits within genome and has inverted repeats either side of it with genes in between which code for it to be excised to another position in the genome

Question 14

What are simple transposons?

Answer 14

Insertion sequences which have additional gene(s) which often code for bacterial resistance

Question 15

What are complex or composite transposons?

Answer 15

Multiple genes which are flanked by insertion sequences

Question 16

What do transposases?

Answer 16

enzymes that identify the inverse terminal repeat sequences within the DNA and proceed to bind and excise (cleave) the DNA transposons in between the terminals

Question 17

What is an integron?

Answer 17

• Special class of composite element which carry gene cassettes
• They can carry multiple resistance genes
• When they are transferred they transfer a whole set of genes together

Question 18

What are the functions of transposons?

Answer 18

• Transfer genes from plasmid to plasmid
• Conjugative transposon transfer from one cell to another (cf conjugative plasmids)
• Transfer genes between plasmid and chromosome
• Pick up chromosomal genes

Question 19

How many cassettes can integrons carry?

Answer 19

Up to 5

Question 20

Describe the mechanism of transformation

Answer 20

• Naked DNA is picked up from the environment

- Can replace existing chromosomal gene with a resistant variant

Question 21

Give an example of a baceria that has become resistant through transformation

Answer 21

Streptococcus pneumoniae (penicillin resistance)

Question 22

Where do resistance genes originate?

Answer 22

• The environment (where bacteria and antibiotic have co-evolved) (e.g CTX-M Beta-lactamase)
• Also can develop resistance to synthetic antimicrobials such as sulphonamides

Question 23

What can be done to tackle antibiotic resistance?

Answer 23

• Develop new antimicrobials
• Monitor spread of resistance
• Antibiotic stewardship (control of prescribing)
• Point of care diagnostics (know immeaditely what bacteria has infected the patient and treat with correct antibiotic accordingly)