MICR 4423 EXAM 5 QUESTIONS AND ANSWERS
What is antibiotic selection? - Answers - Survival of a population of antibiotic resistant
cells within a larger population of antibiotic sensitive cells.
Where can antibiotic selection occur? - Answers - Anywhere where there are antibiotics
and bacteria present. The best-surviving bacteria will be selected for.
Name a common use for antibiotic selection in microbiological research. - Answers - To
identify and isolate cells that have piece of DNA of interest such as a particular plasmid
or gene in the chromosome.
Why does virtually every plasmid used for scientific research contain an antibiotic
resistance marker? - Answers - It allows the cells that contain that plasmid to be
identified through antibiotic selection.
Imagine that you have a sample of bacteria that is a mixture of ampicillin-resistant cells
and ampicillin-sensitive cells. How could you isolate the ampicillin-resistant cells? -
Answers - Plate the cells on an ampicillin plate so that only the ampicillin-resistant cells
will survive and produce colonies.
Distinguish between the Tet-ON and Tet-OFF systems in terms of what inducer addition
does to gene expression and how it occurs at the molecular level. - Answers - In Tet-ON
when you add tet or dox it turns gene expression on. In Tet-OFF when you add tet or
dox it turns tet expression off. Addition of tetracycline always causes tetR to come off its
operator. In Tet-OFF there is a cruddy promoter that requires a transactivation domain
which is bound to TetR. When TetR leaves it takes the transactivation domain with it
and stops gene expression.
What is a typical way of administering Tet to an animal? - Answers - Through its
drinking water.
Contrast how antibiotics are regulated in the United States and northern Europe with
how they are regulated in most other countries. - Answers - In US- prescribed by a
doctor and dispensed by a pharmacist.
Most other countries- over-the-counter in drug stores or even gas stations.
List at least one pro and one con of having antibiotics available by prescription only. -
Answers - Prescription only pro- professional diagnosis means hopefully the appropriate
antibiotic and course of antibiotics is prescribed, there is more accountability, assurance
of product quality...
Con- Requires a lot of infrastructure and money (doctors and pharmacists have to be
paid), slower
, List at least one pro and one con of having antibiotics available over the counter. -
Answers - Pros- faster, cheaper, more available to people in rural areas that do not
have access to a doctor
Cons- Risk of inappropriate treatment (people might choose the wrong antibiotic or not
take it for long enough), risk of development of antibiotic resistance.
What is the most prevalent/biggest use of antibiotics worldwide and in the USA? -
Answers - In agriculture, raising animals for human food consumption.
What effects do antibiotics have when added to animal feed? - Answers - They promote
growth and give the animals reduced instance of disease.
What antibiotic or class of antibiotics do cells containing the bla marker become
resistant to? What about aac? What about cat? - Answers - Bla- ampicillin/any cillin
Aac- aminoglycosides (usually kanamycin)
Cat- chloramphenicol
What are the Tet-ON and Tet-OFF systems typically used for? - Answers - To inducibly
or conditionally control gene expression in eukaryotic systems.
What is a typical inducer of the Tet-ON or Tet-OFF system? - Answers - Plain
tetracycline or (usually doxycycline)
What is meant by growth promotion? - Answers - Faster weight gain, more weight gain
with less food, more protein and less fat in the meat.
How did the advent of antibiotics help enable modern industrial animal production? -
Answers - With less risk of infections you could raise animals in closer confinement
without worrying about the potential spread of disease. Also by causing the animals to
reach market weight more quickly, farmers could turn around more animals and make a
greater profit.
Name a class of antibiotics that is used or not used in animals. - Answers - Almost all
are used. Chloramphenicol is not because its residues are detectable in meat.
Oxazolidinones are not (no linezolid).
Why is monensin considered a generally safe antibiotic in the cattle and dairy
industries? - Answers - It is not a clinical antibiotic used in humans and there are no
documented cases of antibiotic resistance to it.
What is the mechanism of action of monensin? - Answers - It is an ionophore. It allows
sodium ions to cross the cell membrane, enter the bacterial cell, and prevent it from
growing.
What is the generally accepted mechanism for how antibiotics permit animal growth
promotion? - Answers - Antibiotics affect the gut bacteria of animals. It lowers the
What is antibiotic selection? - Answers - Survival of a population of antibiotic resistant
cells within a larger population of antibiotic sensitive cells.
Where can antibiotic selection occur? - Answers - Anywhere where there are antibiotics
and bacteria present. The best-surviving bacteria will be selected for.
Name a common use for antibiotic selection in microbiological research. - Answers - To
identify and isolate cells that have piece of DNA of interest such as a particular plasmid
or gene in the chromosome.
Why does virtually every plasmid used for scientific research contain an antibiotic
resistance marker? - Answers - It allows the cells that contain that plasmid to be
identified through antibiotic selection.
Imagine that you have a sample of bacteria that is a mixture of ampicillin-resistant cells
and ampicillin-sensitive cells. How could you isolate the ampicillin-resistant cells? -
Answers - Plate the cells on an ampicillin plate so that only the ampicillin-resistant cells
will survive and produce colonies.
Distinguish between the Tet-ON and Tet-OFF systems in terms of what inducer addition
does to gene expression and how it occurs at the molecular level. - Answers - In Tet-ON
when you add tet or dox it turns gene expression on. In Tet-OFF when you add tet or
dox it turns tet expression off. Addition of tetracycline always causes tetR to come off its
operator. In Tet-OFF there is a cruddy promoter that requires a transactivation domain
which is bound to TetR. When TetR leaves it takes the transactivation domain with it
and stops gene expression.
What is a typical way of administering Tet to an animal? - Answers - Through its
drinking water.
Contrast how antibiotics are regulated in the United States and northern Europe with
how they are regulated in most other countries. - Answers - In US- prescribed by a
doctor and dispensed by a pharmacist.
Most other countries- over-the-counter in drug stores or even gas stations.
List at least one pro and one con of having antibiotics available by prescription only. -
Answers - Prescription only pro- professional diagnosis means hopefully the appropriate
antibiotic and course of antibiotics is prescribed, there is more accountability, assurance
of product quality...
Con- Requires a lot of infrastructure and money (doctors and pharmacists have to be
paid), slower
, List at least one pro and one con of having antibiotics available over the counter. -
Answers - Pros- faster, cheaper, more available to people in rural areas that do not
have access to a doctor
Cons- Risk of inappropriate treatment (people might choose the wrong antibiotic or not
take it for long enough), risk of development of antibiotic resistance.
What is the most prevalent/biggest use of antibiotics worldwide and in the USA? -
Answers - In agriculture, raising animals for human food consumption.
What effects do antibiotics have when added to animal feed? - Answers - They promote
growth and give the animals reduced instance of disease.
What antibiotic or class of antibiotics do cells containing the bla marker become
resistant to? What about aac? What about cat? - Answers - Bla- ampicillin/any cillin
Aac- aminoglycosides (usually kanamycin)
Cat- chloramphenicol
What are the Tet-ON and Tet-OFF systems typically used for? - Answers - To inducibly
or conditionally control gene expression in eukaryotic systems.
What is a typical inducer of the Tet-ON or Tet-OFF system? - Answers - Plain
tetracycline or (usually doxycycline)
What is meant by growth promotion? - Answers - Faster weight gain, more weight gain
with less food, more protein and less fat in the meat.
How did the advent of antibiotics help enable modern industrial animal production? -
Answers - With less risk of infections you could raise animals in closer confinement
without worrying about the potential spread of disease. Also by causing the animals to
reach market weight more quickly, farmers could turn around more animals and make a
greater profit.
Name a class of antibiotics that is used or not used in animals. - Answers - Almost all
are used. Chloramphenicol is not because its residues are detectable in meat.
Oxazolidinones are not (no linezolid).
Why is monensin considered a generally safe antibiotic in the cattle and dairy
industries? - Answers - It is not a clinical antibiotic used in humans and there are no
documented cases of antibiotic resistance to it.
What is the mechanism of action of monensin? - Answers - It is an ionophore. It allows
sodium ions to cross the cell membrane, enter the bacterial cell, and prevent it from
growing.
What is the generally accepted mechanism for how antibiotics permit animal growth
promotion? - Answers - Antibiotics affect the gut bacteria of animals. It lowers the
