L17 - Resistance to chemo drugs

Question 1

What is drug resistance?

Answer 1

drug no longer effective for treatment

Question 2

3 main negative consequences of resistance to chemo drugs?

Answer 2

Increased mortality

Increased morbidity

Increased cost (new drugs, longer in hospital)

Question 3

Is antibiotic resistance speeding up?

Answer 3

NO - mechanisms are not changing

we are just searching for it more

Question 4

What was the concern for resistant pathogens in late 1990s?

Answer 4

gram-pos pathogens

e.g. Staph, enterococci, MRSA

Question 5

What was the switch of concern for resistant pathogens in early 2000s?

Answer 5

agents found to treat MRSA

conern now to gram-neg pathogens

Question 6

Why are gram-neg better defenders of drugs?

Answer 6

nature of outer membrane - efflux transporters

Question 7

What is estimated annual death toll worldwide by 2050 for AMR resistance?

Answer 7

10mil

reduce $100tril global economic output

Question 8

Why is resistance already found in nature?

Answer 8

due to environments pathogens are found in e.g. soil, neighbouring competitors

Question 9

Do antibiotics CAUSE resistance?

Answer 9

No

but they are SELECTIVE AGENTS that ENRICH PRESENCE of resistant bacteria

Question 10

2 types of acquired antibiotic resistance?

Answer 10

Endogenous (spontaneous)

Exogenous (horizontal)

Question 11

What are mechanisms for transfer of antibiotic resistance in bacteria?

Answer 11

conjugation
transduction
transformation

Question 12

What are genetic vehicles?

Answer 12

carry multiple diff. resistance genes

Question 13

What can act as genetic vehicles?

Answer 13

plasmids
transposons
other mobile genetic elements e.g. SCC

Question 14

What are the mechanisms of resistance?

Answer 14

altered target

decreased uptake

inactivation/modification

bypass

Question 15

What is the altered target mechanism?

Answer 15

mutation/modification or increase of target

change within active site - reduced binding of drug = resistance

Question 16

What can mediate rifampicin resistance in S. aureus?

Answer 16

alteration of RNA polymerase - mutated residues

if any of the multiple contact points to B-subunit are lost - reduction in binding

Question 17

How does methylation of rRNA result in resistance to many drugs?

Answer 17

Cfr methlyase methylates A2503 of 23s rRNA

local perturbation of part of ribosome - reduces binding of drug

Question 18

What was methylation of rRNA initially discovered as?

Answer 18

horizontally-acquired resistance to linezolid in S.aureus

there are MANY more drugs now experiencing resistance

Question 19

How does vancomycin usually interact with enterococci?

Answer 19

forms H-bonds by D-ala-D-ala dipeptide

Question 20

Vancomycin resistance in enterococci?

Answer 20

D-ala-D-lac instead - almost same as D-ala-D-ala but no H-bond formed to enterococci

Question 21

What are the 5 genes carried in vancomycin resistant enterococci?

Answer 21

regulatory
vanR
vanS

structural
vanH
vanA
vanX

Question 22

What do vancomycin-resistant enterococci need to do to cell wall biosynthesis?

Answer 22

new machinery to re-programme biosynthesis

Question 23

What does vanS do?

Answer 23

detects vancomycin at cell surface

signals vanR to switch on structural genes

Question 24

What does vanH do?

Answer 24

catalyses biosynthesis of D-lac from pyruvate pools

Question 25

What does vanA do?

Answer 25

ligase link D-ala to D-lac

Question 26

What dos vanX do?

Answer 26

ensure no D-ala-D-ala if there is - it is cleaved

Question 27

What is VISA

Answer 27

vancomycin-intermediate S.aureus

Question 28

first detected strain of VISA?

Answer 28

Mu50

Question 29

What common thing do all VISA strains have?

Answer 29

significant thickening of cell wall

Question 30

What does thicker cell walls in VISA strains lead to ?

Answer 30

affinity-trapping of vancomycin

Question 31

How does affinity trapping of vancomycin work?

Answer 31

Thicker cell wall = more sites for vancomycin to bind to more free D-ala-D-ala termini - act as decoy sites stop penetration of the bacterium no disruption of cell wall biosynthesis

Question 32

What happens during DECREASED UPTAKE?

Answer 32

reduced permeability (not as common) efflux

Question 33

What can become deleted to reduce DECREASED UPTAKE?

Answer 33

porins

Question 34

Why is deleting porins for decreased uptake risky?

Answer 34

porins are essential route for nutrients places at competitive disadvantage

Question 35

How does B-lactam resistance in P. aeruginosa involved porins?

Answer 35

downregulate OprD porin needs other mechanisms for resistance to occur

Question 36

Are porins deleted in gram-pos?

Answer 36

No do not see remodelling of envelope in gram-pos

Question 37

What is active efflux?

Answer 37

toxic compounds pumped from cell by efflux pump requires proton motive force or ATP

Question 38

How can resistance arise via active efflux?

Answer 38

up-regulation of endogenous pump horizontal acquisition of new pump

Question 39

What does the efflux transporter in gram-pos do?

Answer 39

pumped to extracellular surface

Question 40

What are the 2 efflux transporters in gram-neg?

Answer 40

1) drug pumped into periplasmic space, diffuse out of porins | 2) Multiple drug efflux system, AcrAB/TolC system

Question 41

How does the AcrAB/TolC system in E.coli work? (efflux system)

Answer 41

straddles cytoplasmic and outer membrane AcrB - transporter protein in cytoplasmic membrane - selects and translocates TolC - substrates pass through AcrA - adapter protein - link transporter and outer membrane channel together

Question 42

What happens during ENZYMATIC INACTIVATION or MODIFICATION?

Answer 42

Destruction Modification bacteria produce enzyme recognising antibiotic

Question 43

What are B-lactamases?

Answer 43

resistant to B-lactam antibiotics

Question 44

What do B-lactamases do?

Answer 44

catalyse hydrolysis of cyclic amide bonds of B-lactam ring open ring cannot bind to target sites on PBPs

Question 45

Do gram-neg produce a lot of B-lactamases?

Answer 45

Yes - a problem

Question 46

How many classes of B-lactamases?

Answer 46

4 = A, B, C, D

Question 47

What are the 2 'flavours' of B lactamases?

Answer 47

Serine | metalloenzymes

Question 48

Which are the serine B-lactamases?

Answer 48

A, C, D

Question 49

Which is the metalloenzyme?

Answer 49

B | usually zinc

Question 50

How do Serine B-lactamases work?

Answer 50

key catalytic Ser residue in active site nucleophilic attack on B-lactam ring - opens up similar structure to B-lactam drug target PBPs - BUT they resolve intermediate and release broken B-lactam to TURN OVER MORE MOLECULES

Question 51

Which flavour of B-lactamases can attack wider range of B-lactams?

Answer 51

Metalloenzymes resistance to CARBAPENEMS in ADDITION to penicillins, 1st 2nd 3rd gen cephalosporins

Question 52

Why was carbapenem use increased?

Answer 52

ESBLs - could attack not only penicillins but 1st 2nd 3rd gen cephalosporins

Question 53

What are the 3 diff. families of aminoglycoside modifying enzymes?

Answer 53

ANT - adenyltransferase AAC - acetyltransferase APH - phosphotransferase

Question 54

How do aminoglycoside modifying enzymes work?

Answer 54

transfer bulky groups to specific points on aminoglycoside prevents H-bond contacts with 16s rRNA

Question 55

Add what specific part of amiglycoside to the modifying enzymes add things to?

Answer 55

OH or amino group

Question 56

What happens in TARGET BYPASS

Answer 56

acquisition of alternative target acquire alternative version of drug target insensitive to antibiotic via Horizontal GT native protein targeted but new protein performs same function and works (sometimes grouped with altered target)

Question 57

How does methicillin resistance in S.aureus occur?

Answer 57

MRSA - additional PBP (PBP2a) carries out sufficient cross linking in peptidoglycan insensitive to most B-lactams

Question 58

What is PBP2a encoded by

Answer 58

MecA

Question 59

How does methicillin work in MSSA?

Answer 59

PBPs become inactivated - no cross linking of peptidoglycan

Question 60

Can resistance mechanisms work together?

Answer 60

YES when all mechanisms on their own aren't sufficient, but they are TOGETHER

Question 61

Multiple mechanisms for drug resistance against B-lactams?

Answer 61

deleted porin B-lactamase Efflux pump