MICR 4423 EXAM 4 REVIEW
How do we define antibiotic resistance? - Answers - Continued growth of bacterial cells
in a concentration of an antibiotic that would normally either stop growth or kill the cells.
What is innate resistance to antibiotics? - Answers - The resistance that antibiotic
producers have so that they don't kill themselves with the antibiotics that they produce.
What is one way that an antibiotic producer can protect itself from the antibiotics it
makes? - Answers - - You can do the last step of antibiotic synthesis outside of the cell
that way it doesn't become a real antibiotic until it is leaving.
- A cell could also produce efflux pumps to keep the concentration very low within the
cell; the antibiotic is immediately pumped out of the cell after production.
- Also, there can be enzymes that inactivate the antibiotic if it accumulates within the
cytoplasm.
What is acquired resistance to antibiotics? - Answers - Resistance by non-producers
through the acquisition of antibiotic resistant genes usually via genetic transmission like
horizontal gene transfer.
How can acquired resistance be acquired by cells? - Answers - There can be a new
mutation under antibiotic pressure; a cell is exposed to an antibiotic, it spontaneously
mutates in a way that gives it the advantage, and then they can pass this mutation on
via vertical transmission or via horizontal gene transfer.
What are some common means by which antibiotic resistance genes can be acquired
by cells? - Answers - - Through the uptake of naked DNA from the environment.
- Through bacterial conjugation, also known as bacterial mating.
- Through phage transduction; this is where you have infecting phages accidentally
picking up some genes from a host cell and giving the genes to a recipient cell.
How does resistance compare to tolerance and persistence? - Answers - - Resistance
is typically genetic and allows for cells to grow and thrive in the presence of an
antibiotic.
- Tolerance and persistence both allow for survival under transient exposure to an
antibiotic; tolerance usually applies to the entire population and is mediated by
environmental effects or genetic effects that usually cause cells to grow slower as a
population, whereas persistence is characterized by a small sub-population of cells that
is not growing and, thus, can survive antibiotic treatment if it suddenly comes on.
Additionally, both tolerance and persistence typically are not heritable.
What is meant by the resistome? - Answers - We mean all of the resistance genes or
even resistance mechanisms that exist.
, What is the most common mechanism of resistance to β-lactam antibiotics? - Answers -
β-lactamases are the most common mechanism.
What is the principal difference between transpeptidases and β-lactamases with respect
to enzyme acyl intermediate lifetimes? What step makes all the difference? - Answers -
- Deacylation; the β-lactam antibiotic coming off of the enzyme.
- In a transpeptidase, it forms the intermediate quickly with the enzyme, but then it takes
hours for it to come off. This ties up the transpeptidase, which means that it cannot
work.
- In a β-lactamase enzyme, the β-lactam binds to it quickly, but then it is immediately
kicked off of the enzyme. The purpose of the β-lactamase is to break down the β-
lactam.
What is the difference between genetic and non-genetic resistance? - Answers - -
Genetic resistance is semi-permanent; resistant cells will continue to be antibiotic
resistant even if you grow them again and again in new cultures.
- Non-genetic resistance is typically pretty temporary; you change the conditions and
they are no longer resistant anymore.
What are two examples of non-genetic antibiotic resistance? - Answers - - Persistence;
the small sub-population of cells is temporarily not growing and, thus, insensitive to
antibiotics.
- Biofilm formation; the cells secrete a matrix that protects and encases them.
- Tolerance; we have some kind of condition that causes cells to grow slower, then they
are exposed to an antibiotic for some period of time, and then they will die slower and,
thus, have better survival in the presence of a temporary antibiotic exposure.
Where must β-lactamases be in the cell for them to do their job of inactivating β-lactam
antibiotics? - Answers - They either have to be secreted into the periplasm in the case
of Gram negative bacteria or on the outer face of the cytoplasmic membrane in a Gram
negative or a Gram positive. This is due to the location of the β-lactams.
Why would a bacterial cell want to regulate the production of a β-lactamase so that it is
produced only in the presence of β-lactam antibiotics? - Answers - This is because it
saves energy.
What is the evolutionary origin of β-lactamases? - Answers - Transpeptidases; they
started life as transpeptidases and they have a very similar active site, except they allow
for a much faster deacylation.
What is meant by an extended-spectrum β-lactamase (ESBL)? - Answers - It is a β-
lactamase that can degrade multiple classes of β-lactam antibiotics.
What do KPC from Klebsiella pneumoniae and the class B β-lactamase NDM-1 have in
common? - Answers - They are active against all current β-lactam antibiotics.
How do we define antibiotic resistance? - Answers - Continued growth of bacterial cells
in a concentration of an antibiotic that would normally either stop growth or kill the cells.
What is innate resistance to antibiotics? - Answers - The resistance that antibiotic
producers have so that they don't kill themselves with the antibiotics that they produce.
What is one way that an antibiotic producer can protect itself from the antibiotics it
makes? - Answers - - You can do the last step of antibiotic synthesis outside of the cell
that way it doesn't become a real antibiotic until it is leaving.
- A cell could also produce efflux pumps to keep the concentration very low within the
cell; the antibiotic is immediately pumped out of the cell after production.
- Also, there can be enzymes that inactivate the antibiotic if it accumulates within the
cytoplasm.
What is acquired resistance to antibiotics? - Answers - Resistance by non-producers
through the acquisition of antibiotic resistant genes usually via genetic transmission like
horizontal gene transfer.
How can acquired resistance be acquired by cells? - Answers - There can be a new
mutation under antibiotic pressure; a cell is exposed to an antibiotic, it spontaneously
mutates in a way that gives it the advantage, and then they can pass this mutation on
via vertical transmission or via horizontal gene transfer.
What are some common means by which antibiotic resistance genes can be acquired
by cells? - Answers - - Through the uptake of naked DNA from the environment.
- Through bacterial conjugation, also known as bacterial mating.
- Through phage transduction; this is where you have infecting phages accidentally
picking up some genes from a host cell and giving the genes to a recipient cell.
How does resistance compare to tolerance and persistence? - Answers - - Resistance
is typically genetic and allows for cells to grow and thrive in the presence of an
antibiotic.
- Tolerance and persistence both allow for survival under transient exposure to an
antibiotic; tolerance usually applies to the entire population and is mediated by
environmental effects or genetic effects that usually cause cells to grow slower as a
population, whereas persistence is characterized by a small sub-population of cells that
is not growing and, thus, can survive antibiotic treatment if it suddenly comes on.
Additionally, both tolerance and persistence typically are not heritable.
What is meant by the resistome? - Answers - We mean all of the resistance genes or
even resistance mechanisms that exist.
, What is the most common mechanism of resistance to β-lactam antibiotics? - Answers -
β-lactamases are the most common mechanism.
What is the principal difference between transpeptidases and β-lactamases with respect
to enzyme acyl intermediate lifetimes? What step makes all the difference? - Answers -
- Deacylation; the β-lactam antibiotic coming off of the enzyme.
- In a transpeptidase, it forms the intermediate quickly with the enzyme, but then it takes
hours for it to come off. This ties up the transpeptidase, which means that it cannot
work.
- In a β-lactamase enzyme, the β-lactam binds to it quickly, but then it is immediately
kicked off of the enzyme. The purpose of the β-lactamase is to break down the β-
lactam.
What is the difference between genetic and non-genetic resistance? - Answers - -
Genetic resistance is semi-permanent; resistant cells will continue to be antibiotic
resistant even if you grow them again and again in new cultures.
- Non-genetic resistance is typically pretty temporary; you change the conditions and
they are no longer resistant anymore.
What are two examples of non-genetic antibiotic resistance? - Answers - - Persistence;
the small sub-population of cells is temporarily not growing and, thus, insensitive to
antibiotics.
- Biofilm formation; the cells secrete a matrix that protects and encases them.
- Tolerance; we have some kind of condition that causes cells to grow slower, then they
are exposed to an antibiotic for some period of time, and then they will die slower and,
thus, have better survival in the presence of a temporary antibiotic exposure.
Where must β-lactamases be in the cell for them to do their job of inactivating β-lactam
antibiotics? - Answers - They either have to be secreted into the periplasm in the case
of Gram negative bacteria or on the outer face of the cytoplasmic membrane in a Gram
negative or a Gram positive. This is due to the location of the β-lactams.
Why would a bacterial cell want to regulate the production of a β-lactamase so that it is
produced only in the presence of β-lactam antibiotics? - Answers - This is because it
saves energy.
What is the evolutionary origin of β-lactamases? - Answers - Transpeptidases; they
started life as transpeptidases and they have a very similar active site, except they allow
for a much faster deacylation.
What is meant by an extended-spectrum β-lactamase (ESBL)? - Answers - It is a β-
lactamase that can degrade multiple classes of β-lactam antibiotics.
What do KPC from Klebsiella pneumoniae and the class B β-lactamase NDM-1 have in
common? - Answers - They are active against all current β-lactam antibiotics.
