Antimicrobials

Question 1

Penicillin discovery

Answer 1

It was discovered in 1928 by Alexander Flemming. Bacteria was streaked onto a plate, a fungi was also found growing on the plate. It formed a protective zone around it preventing bacteria from getting near it. This was found to be due to penicillin.
Florey and Chain were able to isolate it and improve activity.
Dorothy Hodgkin found penicillins atomic structure, helping us design derivatives.

Question 2

General Cell wall targeting antibiotics

Answer 2

Penicillin, Cephalosporins, Carbapenems. These are broad spectrum antibiotics. They do not need to enter cells. Considered bacteriolytic, causing cells to lyse.

Question 3

Gram (-) cell wall targeting antiobiotics

Answer 3

Monobactams. Do not need to enter cells. Bacteriolytic, lysing cells.

Question 4

Gram (-) Protein synthesis targeting antibiotics

Answer 4

Aminoglycosides. Enter cells. Target the 30S ribosome subunit. Bacteriolytic, causing cell lysis.

Question 5

Gram (+) Protein synthesis targeting antibiotics

Answer 5

Macrolides. Enter cells. Target 50S ribosome subunit. Bacteriostatic, arresting bacteria in a certain stage.

Question 6

Target DNA replication in any bacteria.

Answer 6

Fluoroquinolones. Enter cells. Broad spectrum antibiotics. Bacteriolytic, causing lysis.

Question 7

Gram (-) cell wall

Answer 7

Inner membrane, thin peptidoglycan layer, outer membrane. Outer membrane has carbohydrates. If the PG layer were thick, then proteins could not connect the inner and outer membranes.

Question 8

Gram (+) cell wall

Answer 8

Inner membrane, thick peptidoglycan layer.

Question 9

Peptidoglycan

Answer 9

Peptidoglycan is a mesh of carbohydrates that form the cell wall of bacteria. These carbohydrates are cross-linked by peptides. The cross link is formed by PBP via transpeptidation. LT, NagZ, and AmpD cleave and remodel PG during cell division.

Question 10

PBP cross-linking

Answer 10

The peptide enters the Active site, where a D-Alanine-D-alanine residue attacks the serine residue, forming a covalent bond. The Peptide chain of another carbon chain enters and attacks this covalent bond, forming a dimer with the peptide and freeing the active site.

Question 11

PBP2 penicillin binding

Answer 11

Penicillin contains a Beta-lactam ring that is similar to the D-alanine-D-alanine residue. The Beta-lactam ring is able to attack the serine residue, forming a covalent bond. Since the next peptide chain can not attack this bond, the penicilin stays bound, preventing cross-linking. The bacteria can no longer form a peptidoglycan layer, meaning the bacteria can no longer resistant external pressure and pops.
All PBPs are targeted by PBPs.

Question 12

Beta-lactam ring

Answer 12

Present in many cell wall targeting drugs, preventing the formation of serine covalent bonds in the active site, preventing cross-linking.

Question 13

Ribosomes

Answer 13

In prokaryotes, ribosomes has 30S and 50S subunits. First, tRNA enters the P site, binding the start codon, and another enters the A site. The Amino Acid from the first tRNA has a peptide bond formed with the A site amino acid. The first tRNA leaves and then second one moves to the P site allowing for a new tRNA to enter and bind its Amino acid. This continues until the exit codon is reached where a tRNA without an AA enters.

Question 14

Aminoglycosides

Answer 14

They were isolated from the bacterium, streptomyces (Streptomycin). It is a very effective drug against gram negative bacteria, targeting the 30S subunit.
It works against some mycobacterium and gram positives.
It enters via polar interactions with the outermembrane. It goes through the cell wall via membrane transporters. It passes the inner membrane by oxygen dependent active transport.
It binds to 30S at the A site, preventing tRNA binding. Stopping protein synthesis, forming truncated peptides.
It is Bacteriocydal as it stays bound for a long time, causing cell death.

Question 15

Macrolides

Answer 15

These target Gram positive bacteria 50S ribosomes. It is impermeable to the outer membrane. But it can freely diffuse through gram positives PG layer and membrane.
It binds between the A site and P site of the 50 ribosome, preventing peptide bonding for AAs, stopping synthesis.
It is bacteriostatic as it only stays bound for a short amount of time, freezing growth and weakening the bacteria.

Question 16

Tetracyclines

Answer 16

These attack both gram positive and gram negative bacteria. It was isolated from streptomyces. It contains a 4 ring structure. It binds to the A site of the 30S ribosome, preventing protein synthesis.

Question 17

Fluoroquinolones

Answer 17

These are entirely synthetic drugs. They can freely diffuse into bacteria, being able to target both types. It was originally made as a biproduct of an antimalarial drug.
It targets DNA. it has 2 rings surrounded by different variable sites that can be changed for specificity. It has two sites (F and Carboxyl group) that can not be changed. It targets DNA gyrase and topoisomerase, causing DNA fragmentation and replication inhibition.

Question 18

Teixobactin

Answer 18

This drug was recently produced by looking at soil bacteria. It is currently going through clinical trials.
They found it by isolating bacteria and putting individual bacteria in wells. Bellow each well is a gram positive bacteria. This would allow any product from the bacteria to land on the strain below. They found Teixobactin which worked as an antibiotic.
It can freely diffuse into any bacteria. It can kill S. aureus without any development of resistance.
Teixobactin takes lipids from the membrane to form its own filaments, a chain of lipids. This forms around the bacteria, forming a protective sheet, preventing movement and survival. This also prevents cell division by acting as a glue

Question 19

Antimicrobial resistance

Answer 19

The 1950s were the golden age for Antibiotics, in terms of efficiency and profits. By the 1970s the market was saturated and GPs reported resistance. After the discovery of Penicillin in 1928, by the 1940s there was resistant Staphylococcus aureus

Question 20

Animal contribution to AMR

Answer 20

When animals are given antibiotics, their bacteria can develop resistance. Then the food produced can carry resistant bacteria.

Question 21

Key resistant bacteria in hospital deaths

Answer 21

E. coli, Klebsiell pneumoniae, enterobacter faecium, psuedomonas aeruginosa, Methicillin resistant staphylococcus aureus (MRSA).

Question 22

Becoming resistant

Answer 22

First there is a lot of bacteria with a few resistant bacteria. Then Antibiotic is applied and the non-resistant bacteria and good bacteria are killed. The surviving resistant bacteria can proliferate. They can then give their resistance to other bacteria.

Question 23

Vertical evolution

Answer 23

A mutagen causes mutagenesis, generating antibiotic resistant bacteria by having modifications in the AB target. This can also be spontaneous.

Question 24

Horizontal evolution.

Answer 24

Conjugation - A plasmid containing the resistant gene is carried by a bacteria and can be transferred to other bacteria.
Transformation - When the bacteria dies, the DNA is fragmented and the fragment carrying the resistance gene can be uptaken into a new cell.
Transduction - A phage can have the resistance gene in its DNA that it injects into the bacteria. This DNA can form a plasmid or be incorporated into the chromosome.

Question 25

Antibiotic resistance mechanisms

Answer 25

Efflux pumps can be produced to pump out the drug.
Uptake can be reduced by decreasing the amount of porins that are used by the AB.
Inactivating enzymes can be produced that inactivate the drug. There can be enzymes that cleave the drug or modify the drug.
Alternative enzymes can be produced that perform the same function as an enzyme targeted by the AB.
The AB target can be altered.

Question 26

AMR against beta-lactam

Answer 26

Altered PBP enzymes can be produced that are not targeted by beta-lactam. This is done by resistant Staph aureus that produce PBP2A.
MexA and B pumps can be used to pump out Beta-lactam.
There can be a loss of outer membrane porins specific to the AB, as seen with Pseudomonas aeruginosa losing its OprD porins for resistance against Carbapenems.

Beta-lactamases can be produced that cleave or modify beta-lactam. It modifies the beta-lactam to an open structure that can no longer bind PBP.

Question 27

PC1 Beta lactamase induction Staphylococcus Aureus

Answer 27

The antibiotic binds the BlaR1 receptor, which then activates the cleavage of its cytoplasmic domain. This coupled with BlaR2, activates the blaZ gene. BlaZ encodes a beta-lactamase.

Question 28

Super Beta-lactamase

Answer 28

New Delhi Beta-lactamase NDM-1.
This was first detected in Klebsiella pneumoniae, conferring resistance to Beta-lactam drugs (Penicillin, Carbapenem, Cephalosporins). It is spreading very quickly, now appearing in E. coli and Enterobacter.

Question 29

Aminoglycoside resistance

Answer 29

Some pseudomonas gain resistance due to transport defects and impermeable membranes.
Most have a mutation that alters the 30S ribosome binding site, so Aminoglycoside can no longer inhibit its function. This mutation still maintains the enzymes function. Many different mutations can form without altering function.

Question 30

Macrolide resistance

Answer 30

They can form increased efflux pumps (MefA), pumping out the drug.
Most often, there is a mutation to the 50S binding site, stopping Macrolide from binding, while allowing the enzyme to function as usual.
Methylase can methylate the 50S in a way that changes the size so Macrolide can not bind without altering its fucntion.

Question 31

Tetracycline resistance

Answer 31

Efflux pumps are produced to pump out the drug. Porins are reduced. The ribosome binding site is altered.

Question 32

Quinolone resistance

Answer 32

Efflux pumps are produced. Penetration reduced with less porins. Mutations in gyrase and topoisomerase prevent binding without altering function.

Question 33

Super bug

Answer 33

Bacteria that have gained multiple resistance mechanisms over time, becoming resistant to multiple different antibiotics.

Question 34

Super bug families

Answer 34

MRSA (methicilin-resistant staphelococcus aureus), VRE (Vancomycin resistant Enterobacter), CRE (Cabrapenem resistant enterbacteriaceae), EBSL-producing Enterobacter, Multidrug resistant psuedimonas aerigunosa, H30-Rx = E. coli strain resistant to Fluoroquinones.

Multi-drug resistant acinetobacter has almost all resistance mechanisms described, living on skin.