Lecture 7 AMR

Question 1

What are beta lactams?

Answer 1

A class of antibiotics that share the beta lactam ring
includes (penicillin’s, cephalosporins, carbapenems, and monobactams)

Question 2

What are suicide inhibitors?

Answer 2

Inhibitors that bind to an enzyme and render it useless by irreversibly binding.

Question 3

Why are antibiotics usually accompanied with suicide inhibitors?

Answer 3

Antibiotics are β-lactams. Bacteria have learned to fight antibiotics by having these enzymes called β-lactamases which cleave and inactivate the β-lactams. But these suicide inhibitors can bind to these enzymes and render them useless, thus protecting the β-lactams. Because of this, suicide inhibitors are known as potentiators of β-lactams.

Question 4

3 Suicide inhibitors

Answer 4

Clavulanic acid
Tazobactum
Sulbactum

Question 5

How many evolutionary families of B lactams are there?

Answer 5

9

Question 6

Whats a Beta lactamase?

Answer 6

An enzyme bacteria have evolved that disrtupts the B-lactam ring and renders the antibiotic useless.

Question 7

What is CTX-M-1

Answer 7

The first CTX resistant family of bacteria.
-discovered in 1989 in Munich, Germany
-isolated from an E. coli ear infection of a 4 year old child
-the bacteria showed resistance to the antibiotic cefotaxime (their lactamases are called cefotaximases)

Question 8

What is CTX-M-2?

Answer 8

-2nd discovery of the CTF evolutionary family
-found in 1989 in Argentina
-isolated from the salmonella typhimurium bacteria in meningitis patients
-it shares 84% of the same amino acid sequence with CTX-M-1
-resistant to cefotaxime (their lactamases are called cefotaximases)

Question 9

Before 2000 what class were most B-lactamases?

Answer 9

TEM or SHV

Question 10

Explain the CTX-M pandemic *****

Answer 10

• There has been an explosive diversification of CTX-M β-lactamases globally
  -Belong to the ESBL group, and are associated with resistance in Enterobacteriaceae
• CTX-M enzymes are evolving so fast they have displaced all other lactamases
• It is constantly mutating and we can’t keep up with it (basically no new drugs are working for it)
• Something about CTX-M β-lactamases has a strong evolutionary advantage as it is outcompeting all others
• Some strains now even have resistance to inhibitors

Question 11

What is the blaCTX-M gene?

Answer 11

It is a gene that codes for an enzyme that can cleave cephalosporins

Question 12

What is the most widely disseminated (widely spread) β-lactamase?

Answer 12

CTX-M-15

Question 13

How do they think genes from kluyvera crossed over to other resistant bacteria?

Answer 13

By being mobilized onto plasmids

Question 14

How large of plasmids can bacteria have? **

Answer 14

Studies have shown they can carry plasmids that are just as large as their chromosomes. When this was found it blew scientists away as they thought the fitness cost of having plasmids this big would be too high

Question 15

How did CTX-M bacteria evolve to have a strong gene promoter?

Answer 15

Insertion elements (component of transposons) containing strong promoters inserted a strong promoter onto CTX-M genes (giving the needed boost to express)
- Having a strong promoter always turned “on” gave a survival advantage under antibiotic pressure

Question 16

How were bla genes originally expressed in the kluyvera species they came from?

Answer 16

They were only needed when there was competition for nutrients by other microbes. As such they were weakly expressed and tightly regulated.

Question 17

What are integrative and conjugative elements (ICE)?

Answer 17

• Mobile genetic elements in bacteria
• Drive rapid evolution of plasmid genome
• Passed on through conjugation
  Essentially they allow bacteria to evolve fast.

Question 18

What are transposons?

Answer 18

genetic elements capable of inserting and removing themselves from the genome. They often contain genes for antibiotic resistance and metal tolerance.

Question 19

What are high risk clones?

Answer 19

Bacterial clones of E. coli and K. pneumoniae that enhance the spread of antibiotic resistance

Question 20

What are extended-spectrum beta-lactamases (ESBLs)?

Answer 20

β-lactamases that can evade the effect of inhibitors, inhibit beta-lactams (ie. Penicillin), and allow the cell to continue cell wall synthesis (good for bacteria)
Ex. CTX-Ms, TEM, SHV

Question 21

How many CTX-M types of beta-lactamases are there?

Answer 21

99

Question 22

How are new enzyme types in beta lactamases born?

Answer 22

Point mutations in beta-lactamases resulting in altered amino acid sequences. These altered sequences can change the nature of the molecule’s interaction with cephalosporins, and thus result in altered enzyme function. Cephalosporin is pretty large so to evolve to attack it, the lactamase sort of changed shape so it can reach cephalosporin now. Downside is the reduced stability of the enzyme.

Question 23

What are Multiple Drug Resistance plasmids (MDRs)? **

Answer 23

Plasmids that can become established such that they are stably passed from one generation to another if it confers a survival advantage.

• They are natural to Enterobacteria and existed before cephalosporin selection pressure.

Question 24

What is consistent among all CTX-M families?

Answer 24

All can hydrolyze/cleave cefotaxime (3rd generation cephalosporin)
- Varying resistance to the inhibitors

Question 25

What is different about the evolution of CTX-M versus TEM and SHV?

Answer 25

Unlike the TEM and SHV enzymes, the CTX-M enzymes did not evolve from point mutations in the parent enzymes. CTX-M evolved from many evolution events.

Question 26

What are some contributing genetic events for the evolution of CTX-M High Risk Clones?

Answer 26

• Mobilization of klu genes (multiple independent events)
• Random mutation (constantly occurring)
• Integration into plasmids - recombination events
• Promoter acquisition
• Horizontal transfer (speeds evolution)
• Divergent evolution (new enzyme types created)
  Convergent evolution - multiple mobilizations of klu genes

Question 27

What are examples of integrative and conjugative elements (ICE)?

Answer 27

• Transposons
• Insertion elements
• MITES
• Integrative conjunctive plasmids
• Mobile integrons
• Phages