Topic 5: Antimicrobial agents and resistance

Question 1

what does an antiseptic do

Answer 1

kill bacteria, viruses and protozoa, too harsh for internal use
skin

Question 2

what does a disinfectant do

Answer 2

kill bacteria, viruses and protozoa, too harsh for internal use
surfaces

Question 3

what are antibiotics

Answer 3

Low molecular mass compounds that kill or inhibit the growth of bacteria and can be
ingested or injected into the human body with minimal side effects

Question 4

what are the requirements of an antibiotic

Answer 4

killing/inhibition
- bacteriostatic ok for intact immune system, defective needs bactericidal

selective toxicity
- differences between host and pathogen

pharmacokinetics
- does it get where it needs to

Question 5

what makes a good antibiotic

Answer 5

Few side effects
Broad spectrum (symptoms often common between causes)
BUT may destroy natural flora allowing other organisms in (yeast vaginitis)

Question 6

what are the antibiotic targets

Answer 6

cell wall biosynthesis
nucleic acid synthesis
protein synthesis
cytoplasmic membrane function

Question 7

antibiotic targets - cell wall biosynthesis

Answer 7

peptidoglycan is unique to bacteria and essential for viability

beta-lactams - bind and inhibit penicillin binding proteins which are involved in transpeptidation and transglycosylase reactions

glycopeptides - bind to D-ala-D-ala prevent transpeptidation and transglycosylase reactions -last resort due to toxicity

Question 8

what are Transpeptidase and Transglycosylase Reactions (google bard)

Answer 8

Transpeptidase reaction: This enzyme links short sugar chains together in the peptidoglycan by forming bonds between amino acids (proteins). By mimicking this building block, β-lactam antibiotics essentially block the transpeptidase’s “active site,” preventing it from attaching new sugar chains.

Transglycosylase reaction: This enzyme builds the sugar backbone of peptidoglycan by linking sugar molecules together. Glycopeptide antibiotics interfere with this process by hindering the transglycosylase enzyme from doing its job

Question 9

antibiotic targets - nucleic acid synthesis

Answer 9

targets include inhibiting the synthesis of precursors which are not made by humans (in diet)
inhibit DNA gyrase (supercoiling)
RNA polymerase (rifampicin)

Question 10

antibiotic targets - protein synthesis

Answer 10

bacteria ribosomes are different to human ones
can bind to the 50S subunit and block the transfer of peptides
or bind the 30S to prevent it binding to 50S - comes with more side effects eg. kidney function/hearing loss
or bind 30S to prevent alignment of aminoacylate tRNA with mRNA.

Question 11

antibiotic targets - cytoplasmic membrane function

Answer 11

leak H+ pmf dissipate

Question 12

eg.s of beta-lactams

Answer 12

penicillin, methicillin, cephalosporins

Question 13

what is the definition of resistance

Answer 13

A resistant organism is one that will not be inhibited or killed by
an antibacterial agent at concentrations of the drug achievable in
the body after normal dosage

Question 14

what are the causes of resistance - healthcare

Answer 14

over prescription (no diagnosis, misdiagnosis)
over the counter
improper use by patients

Question 15

what are the 2 types of resistance

Answer 15

innate: natural - lack of target/impermeable
acquired: can be through reduced uptake, efflux, inactivation of drug or alteration of target

Question 16

what are the causes of resistance - agriculture

Answer 16

this can be caused by the use of antibiotics for increased growth, prophylaxis or treatment of disease

spreads to humans through contact consumption or the environment

Question 17

what is the genetic basis of resistance

Answer 17

point mutations
new genetic material
conjugation (direct DNA transfer)
transposons
plasmids

Question 18

tackling antibiotic resistance

Answer 18

drug development - empirical screening and rational design
vaccines - Community acquired bacterial infections
Hospital acquired bacterial infections
Viral infections
Veterinary vaccines

Question 19

Acquired Antimicrobial Resistance: Reduced Uptake Method

Answer 19

Reduced Uptake - Outer membrane porins are non-specific channels, a single mutation can increase resistance 5-10 fold for many drugs - which can quickly spread through a population

Question 20

Acquired Antimicrobial Resistance: Efflux Method

Answer 20

Efflux - Multidrug resistance (MDR) exporter (AcrB in E.coli) Tetracycline actively pumps out the drug from within the cell (if it operates intracellularly)

Question 21

Acquired Antimicrobial Resistance: Inactivation of Drug Method

Answer 21

e.g. Beta-lactamase hydrolyses the lactam ring of penicillin (common in gram negative bacteria)

Question 22

Acquired Antimicrobial Resistance: Alteration of target Method

Answer 22

e.g. Beta lactams -> alteration in Penicillin Binding Proteins (PBP) e.g. mosaic PBP encoding genes in Streptococcus pneumoniae

Question 23

What structure (viral-phage-like particles in bacteria) protects bacteria from toxic substances?

Answer 23

Encapsullins

Question 24

What are the current notable cases of growing antibiotic resistant pathogens?

Answer 24

MRSA (VRSA)
Mycobacterium Tuberculosis -> costing 1 billion dollars to NY alone.
NDM-1 in E.coli resistant against carbapenem.

Question 25

What are the requirements for scalable diagnostic techniques?

Answer 25

Rapid, achievable at point of care, and cheap.

Question 26

What are the benefits of large scale vaccination projects?

Answer 26

-Reduce the number of bacterial infections requiring antibiotics (reducing developing resistance)
-Reduce the number of infections (hospitalisations and fatalities)
-Reduce the number of viral infections in which antibiotic unnecessarily given.

Question 27

Properties of conjugative plasmids:

Answer 27

Self transmissible (>25kb), mobilisable, can carry multiple resistance genes

Question 28

What are the qualities of an ideal antibiotic target:

Answer 28

Present in bacterium but not in human and essential for the pathogen’s survival.

Question 29

Examples of glycopeptide antibiotics:

Answer 29

Vanomycin, teichoplanin

Question 30

Examples of beta-lactams antibiotics:

Answer 30

Penicillin, methicillin, cephalosporins

Question 31

What are examples of new antibiotics?

Answer 31

Synercid, Linezolid and Daptomycin

Question 32

What is Synercid?

Answer 32

A new antibiotic which is a mixture of dalfopristin and quinupristin (mixing drugs makes bacteria more susceptible) -> both are streptogramins (binding to the 50S subunit of the ribosome) and inhibits translation (by preventing peptide elongation) -> resistance has developed due to use in agriculture.

Question 33

What is Linezolid?

Answer 33

A new antibiotic which is a oxazolidinone, binding to the 50S subunit of the ribosome and preventing the initiation of protein synthesis

Question 34

What is Daptomycin?

Answer 34

A new antibiotic which interacts with many sites across the target weakly on the cell surface, the culmination of these weak interactions (and multiple insertions in the membrame) leads to the formation of a pore in the membrane -> its mechanism of lysis is unknown but is linked to the pumping of K+ out of the cell and is Ca2+ dependent. Because of its unique mechanism it’s able to treat “undruggable” targets -> however resistance developed in 2005.

Question 35

Why are bactofilins a good target when using a mixture of drugs in an antibiotic mixture?

Answer 35

Targeting bactofilin makes the targeted cell 50x more sensitive to cell wall targeting antibiotics

Question 36

What is an example of a disinfectant?

Answer 36

Lister’s phenol -> can cause burns on skin