Resistance

Question 1

Resistance

Answer 1

A disease causing age can survive and grow in the presence of concentrations of a chemotherapeutic agent that can safely be achieved in a patient. The drug no longer acts to kill/inhibit the disease causing agent

Question 2

Consequences of resistance

Answer 2

Increase mortality. Increased morbidity from longer illness and increased spread of restistant organisms. Increased cost from prolonged hospital stays and novel drug costs.

Question 3

MRSA

Answer 3

Mean population-weighted prevalence in Europe in 2014 was 17.4 (Hassoun et al, 2017). Methicillin-resistant Staphylococcus aureus. Achieved by bypass pathway from that inhibited by drug.

Question 4

Mortality predictions of resistance

Answer 4

In 2050 10 million deaths will be due to antimicrobial resistance.

Question 5

Mechanisms of antimicrobial resistance acquisition

Answer 5

Endogenous spontaneous mutation leads to resistance. Horizontal gene transfer from a pre-resistant organism (either from intrinsic resistanfce or from the antibiotic-producer organism)

Question 6

Mechanisms of horizontally acquired ABx resistance

Answer 6

Genetic vehicles e.g. plasmids, transposons, or Mechanisms of transfer e.g. conjugation, transduction and transformation

Question 7

Cause of resistance to emerge

Answer 7

Selection pressure of ABx drives survival of the fittest evolution.

Question 8

Mechanisms of resistance

Answer 8

Altered target site.
Inability to gain adequate, intracellular drug concentrations.
Modification or degradation of drug by enzymes
New, bypass pathway to avert that inhibited by drug.

Question 9

Risk factors of an ABx or a bacteria for resistance

Answer 9

ABx which act at a singular binding target site.
Bacteria which are naturally transformable species (able to take up DNA fragments in environment and incorporate them into their genome).
Mosaic gene for target of drug

Question 10

Mechanisms for altered target sit

Answer 10

Modification of drug target.
Mutation. of drug target.
Overproduction of drug target.

Question 11

Mechanisms for inadequate, intracellular drug concentrations

Answer 11

Poor drug uptake.

Active efflux of drug.

Question 12

Example of mutated target site

Answer 12

Rifampicin and S.aureus. Mutation in a single amino acid of 4 different residues will cause a huge reduction in the affinity which Rifampicin can bind to RNA polymerase and decrease the drugs activity.

Question 13

Example of mosaic gene resistance

Answer 13

Penicillin binding protein gene is mosaic and recombinant in Neisseria and Streptococcus due to species being naturally transformable, create altered target for beta-lactams.

Question 14

Modification of drug target definition and example

Answer 14

NOT GENETIC CHANGE. Post-translocational changes. e.g. Vancomycin resistant enterococci. Create d-alanine-d-lactate able to be used in cell wall biosynthesis but no H bond can form with Abx. Decrease affinity. Minimum change in 5 genes - vanR, vanS, vanH, vanA, vanX.

Question 15

5 genes in vancomycin resistant enterococci

Answer 15

vanR - signal transduction of vanS message.
vanS - sense presence of vancomycin.
vanH - synthesise d-lactate from raw materials.
vanA - ligase to form d-ala-d-lac bonds.
van x - peptidase, breaks existing d-ala-d-ala bonds.

Question 16

Example of increase target expression resistance

Answer 16

Vancomycin resistant S.aureus, lead to much thicker cell wall. Causes therapeutic failure but not full resistance

Question 17

Origin of vancomycin resistant enterococci genes

Answer 17

Acquisition from soil microbe which produces vancomycin and prevents it from being effected by the chemical.

Question 18

Example of decreased permeability resistance, most common organisms and drawbacks of mechanism

Answer 18

Mostly gram negative. organisms e.g. beta-lactam resistant Pseudomonas aeruginosa. Limits nutrient influx.

Question 19

Anti-cancer drug active efflux resistance example

Answer 19

Antibiotic agents: doxirubicin, bleomycin. Vinca alkaloids. Topoisomerase 2 inhibitor etoposide. Due to p-glycoprotein ATP efflux pump from ATP-binding cassette transporter family. Present in healthy cells but expression can be amplified in cancer cells.

Question 20

Antibiotic active drug efflux example

Answer 20

AcrAB/TolC System in E. coli gives resistant to range of ABx including aminoglycosides, tetracyclines, beta-lactams, macrolides, fluoroquinolones.

Question 21

2 Examples of degradation of drug by enzyme

Answer 21

beta-lactamases degrade beta-lactams. opens ring structure. Aminoglycoside modification adenylation, acetylation or phosphorylation which prevents drug binding to 16S ribosome RNA.

Question 22

Class A beta-lactamases

Answer 22

Extended spectrum beta-lactamases. Serine mediated

Question 23

Class B beta-lactamases

Answer 23

Carbapenemases. Widest spectrum. Metallo/zonc mediated

Question 24

Class C beta-lactamases

Answer 24

Cephalosporinases, AmpC enzymes. Serine mediated

Question 25

Class D beta-lactamases

Answer 25

Oxacillinases. Serine mediated. Earliest detected.

Question 26

Enzymes in amino glycoside modification

Answer 26

AAC (acetyltransferases), ANT (adenyltransferases), APH (phosphotransferases)

Question 27

Example of target bypass resistance

Answer 27

Methicillin resistant S.aureus carry MecA gene which codes for PBP2A. This is able to carry out function of PBP to enough extent to cause cross-linking of peptidoglycan but not acted on by methicillin. E.faecium and PBP5 similar mechanism.

Question 28

Beta-lactam restante mechanisms

Answer 28

Beta-lactamases modifying drug. Alter target/PBP in Neisseria and Streptococcus species. Decrease permeability in beta-lactam resistant Pseudomonas aeruginosa

Question 29

P-glycoprotein and agents resistance

Answer 29

P-glycoprotein and ABC transporter presence decrease intracellular drug concs of naturally occurring chemotherapy agents which have hydrophobic aromatic ring and positive charge at a neutral pH. E.g. Vinca alkaloids, Dactinomysin and anthrcycline antibiotics, topoisomerase 2 inhibitors.

Question 30

2 examples of resistance to the antifingal class Azoles

Answer 30

Candida are resistant via active efflux of drugs via an ATP binding cassette transporter from CDR genes. C.albicans are resistant via altered target - lanosterol 14-alpha demethylase is over-expressed and has a mutation at ERG11 to decrease affinity.

Question 31

Overcome p-glycoprotein resistance

Answer 31

Administer calcium channel blocker e.g. verapamil to inhibit pump but has ADRs.

Question 32

Natural expression of p-gp

Answer 32

kidney, liver, gastrointestinal tract, the endothelial cells of the brain and testis, adrenal glands, bone marrow stem cells, and normal peripheral blood lymphocytes