Antibiotic Resistance Flashcards
How do some bacteria become resistant to beta lactam antibiotics? Give an example of a beta lactam antibiotic.
Example = Penicillin
Some bacteria encode for a mutant gene that synthesises antibiotic degrading enzymes. The bacteria is able to do this as the bacterial plasmid synthesises mRNA and as the plasmid carries the resistant genes. This gene is incorporated in protein synthesis when the mRNA is read by the ribosome. This protein has the potential to then go on to become the antibiotic degrading enzymes.
Bacteria resistant to beta lactam antibiotics encode for beta lactamases, an enzyme which degrades beta lactam rings. In order for beta lactam antibiotics to be active the ring must be closed. However when the bacteria encounters the beta lactam ring, the beta lactamase enzyme degrades it (opens) thus penicillin will have no effect on the bacteria.
How do bacteria become resistant to Tetracycline?
The antibiotic resistant gene may also encode for an efflux pump. An efflux pump is found on the membrane of the bacteria. The bacteria uses the efflux pump to pump out the antibiotic from the cell. Therefore, tetracycline will have no effect on the bacteria because it is pumped out.
How do bacteria modify the antibiotic binding target? Give examples of antibiotics this effects.
Antibiotics can also encode for a gene that modified the antibiotic binding target.
Penicillin (beta lactam) targets penicillin binding proteins (found in peptidoglycan layer of the bacteria). However, if the bacteria has the mutant gene to modify the PBP (changing the structure of the protein), the penicillin isn’t able to bind to the protein anymore because the structure has changed.
A great example of this type of resistance is found in the MRSA bacteria (resistant to the antibiotic methicillin). Methicillin won’t work because the protein that methicillin binds onto is modified within the bacteria therefore the antibiotic has no effect.
How do bacteria acquire resistant genes?
2 ways -
- Vertical gene transfer
- Horizontal gene transfer
What is vertical gene transfer?
This is when the resistant gene is passed through bacterial replication. The bacteria actually acquired the gene through evolution e.g. spontaneous mutations can occur for a resistant gene.
This is rare
What is horizontal gene transfer?
The resistant gene is transferred to a bacteria through 3 different means.
- Conjugation
- Transduction
- Transformations
What is conjugation?
Bacteria contains a plasmid with a resistant gene for a particular antibiotic. The bacteria can form a pilus that will attached to the other bacteria. The plasmid containing the resistant gene can be replicated and passed onto the other bacteria.
What is transduction?
Happens through a virus called a bacteriophage.
Bacteria has a resistant gene within it already. A bacteriophage is a virus that only attacks bacteria through injecting its phage DNA into the bacteria. The phage DNA can incorporate itself into the bacterial DNA. After some time has passed, the phage DNA will leave the bacterial DNA and begin replicating, destroying the bacterial DNA in the process. The resistant gene that was part of the bacterial DNA will be floating around inside the damage bacteria. The viral DNA is being replicated and the new bacteriophages are being formed within the bacteria. The new viruses that are being formed will pick up the viral DNA that was replicated. The viral replication will cause the bacteria to lyse, releasing the virus (the bacteriophages containing phage DNA out). However, there will be a bacteriophage that contains a resistant gene from the bacteria because it accidentally packed the resistant gene of the bacteria instead of its own viral DNA. So the bacteriophage containing the resistant gene can attack another bacteria, but instead it will give a resistant gene to the bacteria.
What is transformation?
Another bacteria containing a resistant gene lyses. This releases the resistant gene which can be picked up by another bacteria. The other bacteria will then incorporate it into its genome allowing it to become resistant to some form of antibiotic
