3. Molecular Mechanisms That Confer Antibacterial Drug Resistance And Development Of New Antibiotics To Circumvent Resistance

Question 1

What are the three classes of antibiotic resistant pathogens that are a major threat to human health?

Answer 1

1. MRSA (methicillin resistant staphylococcus arreus
2. Drug resistant gram negative bacteria
3. Drug resistant mycobacterium tuberculosis

Question 2

What is MSRA?

Answer 2

How 80% staph infections are resistant to penicillin , and around 19000 deaths/per year are due to MRSA

Question 3

Example of drug resistant gram negative bacteria?

Answer 3

Klebsielle pneumoniae

Question 4

What is drug resistant mycobacterium tuberculosis?

Answer 4

The leading cause of death from infectious disease

Question 5

What are increased antibiotic resistance correlated with?

Answer 5

Increased antibiotic use (eg 1.4 million kg of antimicrobial drugs annually- 1/2 inappropriately prescribed)

Question 6

How many antimicrobial drugs are used in animal feeds/year?

Answer 6

14 million kg

Question 7

What are the two types of resistance to antibiotics?

Answer 7

1. Inherent “natural” resistance

2. Acquired resistance

Question 8

Examples of inherent resistance?

Answer 8

Inaccessibility of antibiotic

Extrusion of antibiotic genes- found in bacterial chromosomes

Question 9

Describe acquired resistance?

Answer 9

Previously susceptible

Resistance in sub populations or strains of bacterial species

Question 10

Two types of ways to acquire resistance?

Answer 10

1. Vertical gene transfer

2. Horizontal gene transfer

Question 11

What is vertical gene transfer?

Answer 11

The transfer of spontaneous resistance gene mutations in the bacterial chromosome to bacterial progeny during DNA replication

Question 12

What is the speed of vertical gene transfer resistance like?

Answer 12

Fast, despite mutation being a rare event, the fast growth of bacteria and absolute number of cells attained means it’s fast- spontaneous mutation frequency for antibiotic resistance is 10^-8 -10^-9

Question 13

What is the process of vertical gene transfer a matter of?

Answer 13

Darwinian evolution driven by natural selection (in a selective environment of the antibiotic, the wild type are killed while resistant can grow and flourish

Question 14

What is horizontal gene transfer?

Answer 14

Genetic material contained in small packets of DNA can be transferred between individual bacteria of the same species or even between different species

Question 15

Three mechanisms of horizontal gene transfer?

Answer 15

1. Conjugation
2. Transduction
3. Transformation

Question 16

What is the main mechanism of horizontal gene transfer?

Answer 16

Conjugation

Question 17

What is conjugation?

Answer 17

Transmission of resistance genes following direct contact between two bacteria via pilus (like a bridge)

Question 18

What are the key players in conjugation and what do they do?

Answer 18

Plasmids, located in the cytoplasm of the donor and recipient cell and exchange through the pilus

Question 19

What does conjugation resistance transfer allow for?

Answer 19

Resistance to spread among a population of bacterial cells much faster than simple mutation and vertical gene transfer would permit

Question 20

What is transduction?

Answer 20

Antibiotic resistance genes are transferred between two closely related bacteria by means of bacteria specific viruses (bacteriophages)

Question 21

What happens in transduction?

Answer 21

Resistance genes are integrated into the chromosome of the recipient cell

Question 22

What is transformation?

Answer 22

When naked DNA is released into the external environment, normally due to death and lysis of an organism and is taken up by another bacterium

Question 23

How does transformation work?

Answer 23

The antibiotic resistance gene. And be integrated into the chromosome or plasmid of the recipient cell

Question 24

What are the three principal resistance mechanisms for bacterial survival?

Answer 24

1. Efflux pumps
2. Enzymatic degradation of antibiotic
3. Enzymatic modification of antibiotic

Question 25

How do efflux pumps work?

Answer 25

They pump antibiotics back out of bacterial cells through efflux pump proteins to keep intracellular drug concentrations below therapeutic levels

Question 26

Why does efflux pumps work?

Answer 26

Because for antibiotics to be effective, they must reach their specific bacterial targets and act in some reasonable time frame

Question 27

What are efflux pumps variants of?

Answer 27

Membrane pumps possessed by all bacteria to move molecules in and out of cells

Question 28

What is an example of resistance via efflux pumps?

Answer 28

Resistance to tetracyclines- concentrations too low to block protein synthesis

Question 29

What is enzymatic degradation of antibiotic?

Answer 29

The antibiotic is destroyed by chemical modification by an enzyme that is elaborated by the resistant bacteria

Question 30

Example of enzymatic degradation of antibiotic?

Answer 30

The hydrolytic deactivation of the B-lactam ring in the penicillin by expression of a hydrolytic enzyme b-lactamase by resistant bacteria

Question 31

How is B-lactam antibiotics destroyed before it can reach its target?

Answer 31

Lactamase-producing Gram positive bacteria secretes the enzyme into the periplasm

Question 32

How many penicillin molecules can a single B-lactamase hydrolyse per second?

Answer 32

1000 (so if 10^5 enzymes secreted per resistance cell, then 100 million molecules of penicillin are destroyed every second)

Question 33

What is enzymatic modification of antibiotic?

Answer 33

Antibiotic is modified by an enzyme so it's no longer effective

Question 34

Types of resistance enzymes that modify antibiotics?

Answer 34

Acetyl transferase | Phosphoryl transferase

Question 35

What can happen to the antibiotic chloramphenicol?

Answer 35

It can be enzymatically inactivated by the addition of an acetyl or GO sphere group

Question 36

What do modifications to antibiotics do?

Answer 36

Decorate the periphery of the antibiotic and interrupt binding to ribosomes

Question 37

When was the innovation gap in medicine?

Answer 37

1962 to 2000

Question 38

When was the golden age of discovery?

Answer 38

1940-1960 (eg sulfa drugs, b-lactams) - natural discovery

Question 39

When was the golden age of medicinal chemistry?

Answer 39

1990-2010(e.g lipopeptides)

Question 40

What are 3 approaches to develop new antibiotics to circumvent resistance?

Answer 40

1. Modification of common core structures of different antibiotic classes using medicinal chemistry 2. Identification of new antibiotic scaffolds through searches of underexplored ecological niches and bacterial taxa 3. Bioinformatic analysis of bacterial genomes

Question 41

What is the modification of common core structures of different antibiotic classes using medicinal chemistry?

Answer 41

Synthetic tailoring is widely used- scaffolds are black, peripheral chemical modifications are red

Question 42

Examples of modification of core structures?

Answer 42

Penicillin (Original) Toglicino (end result)

Question 43

Two ways tetracycline can be modified?

Answer 43

1. Scaffold can be chemically modified (creating a tetracycline derivative like tigecycline that no longer is a substrate for the efflux pump 2. A new scaffold like retapumulin can be used instead of tetracycline, as it's not a substrate for the efflux pump

Question 44

What's the identification of new antibiotic scaffolds through searches of underexplored ecological niches like?

Answer 44

More than 2/3 of clinically used antibiotics are natural products or their semisynthetic derivatives

Question 45

Describe bioinformatic analysis of bacterial genomes?

Answer 45

The genome sequences of large numbers of bacteria and fungi reveal up to two dozen silent clusters for natural product biosynthesis and a variety of approaches have been used to turn on silent biosynthetic gene clusters to evaluate the novelty and activity of the resultant small molecules