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BIO251 Exam 3 HW: Questions & Accurate Solutions
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BIO251 Exam 3 HW: Questions & Accurate Solutions
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BIO251 Exam 3 HW: Questions & Accurate SolutionsPolio is transmitted by ingestion of water contaminated with feces containing
polio virus. What portal of entry does polio virus use? Right Ans - mucous
membranes only
The ID50 is
the dose that will cause an infection in 50 percent of the test population.
the dose that will kill 50 percent of the test population.
the dose that will kill some of the test population.
a measure of pathogenicity.
the dose that will cause an infection in some of the test population. Right
Ans - the dose that will cause an infection in 50 percent of the test population.
Bacterium Portal of Entry ID50
Staphylococcus aureus Wound <10
Staphylococcus aureus Wound + Ampicillin 300
39) Table 15.1 shows the ID50 for Staphylococcus aureus in wounds with and
without the administration of ampicillin before surgery. Based on the data, the
administration of ampicillin before surgery
A) decreases the risk of staphylococcal infection.
B) increases the risk of staphylococcal infection.
C) has no effect on risk of infection.
D) replaces tetracycline.
E) The answer cannot be determined based on the information provided.
Right Ans - A
A pathogen that is capable of antigenic variation can Right Ans - avoid host
immune defenses
Bacteria such as E. coli and Salmonella produce invasins that bind host cells,
thus causing the cells to Right Ans - engulf the bacteria
Exotoxins and endotoxins are two fundamentally different types of bacterial
toxins. In this activity, you will determine whether each of the following
statements applies to exotoxins or endotoxins. Some statements may apply to
both types of toxins.
,Drag each statement to the appropriate box, indicating whether the statement
applies to exotoxins, endotoxins, or both exotoxins and endotoxins Right
Ans - Exotoxins: 1. These toxins are produced and secreted by actively
growing cells. 2. The host typically responds by producing antibodies called
antitoxin. 3.These toxins may be toxic in very tiny (nanogram) amounts.
4.These toxins may be produced by gram-negative or gram-positive bacteria.
5. Examples include tetanus toxin, cholera toxin, and staphylococcal
enterotoxin. 6.These toxins may be found in foods but are usually inactivated
by cooking.
Endotoxins: 1. These toxins are often released upon phagocytosis of or death
of bacterial cells. 2. This toxin may survive sterilization techniques and
contaminate medications and medical devices even though the medication or
device is completely free of bacteria. 3. These toxins are produced exclusively
by gram-negative bacteria. 4. These toxins are responsible for much of the
pathology caused by Salmonella typhi and Neisseria meningitidis.
Both exo and endo: 1. These toxins may be lethal to the host 2.These toxins
are produced by bacteria but not by viruses.
Mechanisms of Exotoxins and Endotoxins - Foundation Figure 15.4
Part B - Mechanism of Action of A-B Exotoxins
The majority of exotoxins are A-B toxins, which are composed of two
polypeptide subunits referred to as A and B.
The B component functions to bind or attach to the host cell, whereas the A
component exerts its toxic effects on the cell. This activity asks you to place
the images in the correct order as they occur when an A-B toxin interacts with
the host cell.
Drag the images below into boxes to indicate the correct order of events
illustrating the mechanism of action of an A-B exotoxin. Right Ans - Correct
You have correctly placed each of the steps in the mechanism of action of a
typical A-B exotoxin.
An understanding of this process may reveal possible strategies to block or
inhibit it and potentially prevent or reduce toxin-mediated damage to the
host.
, Which of the following strategies might be used to block the activity of an A-B
toxin?
Select all of the strategies below that might inhibit or block the action of an A-
B toxin. Right Ans - 1. blocking host cell receptors to which A-B toxins bind
2. blocking receptor-mediated endocytosis in cells targeted by the A-B toxin
3. inhibiting the secretion of proteins from a bacterial cell
4. blocking the binding sites on the B portion of an A-B toxin
5. blocking separation of the A and B components of the toxin
Consider the structure of a plasma membrane. Select the mechanisms through
which a toxin is likely to disrupt the plasma membrane of a host cell.
Select all that apply. Right Ans - 1. insertion of a protein channel in the host
cell plasma membrane
2. disruption of phospholipid bilayer
Select the statements that correctly describe endotoxins Right Ans - 1.
Endotoxins may cause a life-threatening drop in blood pressure known as
endotoxic shock.
2. Endotoxins can cause fever, chills, weakness, and fatigue.
3. Symptoms caused by endotoxins may actually worsen after treatment of an
infection caused by gram-negative bacteria.
4. Sterilized items may contain endotoxins and cause a reaction in a patient.
Drag the images into the labeled targets to reflect the correct order of steps by
which gram-negative bacteria can bring about a fever response. Right Ans -
In general, the LD50 for exotoxins is much greater than the LD50 for
endotoxins. Right Ans - False
In mice, the LD50 for staphylococcal enterotoxin is 1350 ng/kg, and the LD50
for Shiga toxin is 250 ng/kg. Which of the following statements is true?
Right Ans - Shiga toxin is more lethal than staphylococcal enterotoxin
Antibiotics can lead to septic shock if used to treat Right Ans - gram-
negative bacterial infections.
Which of the following contributes to the virulence of a pathogen? Right
Ans - numbers of microorganisms that gain access to a host, evasion of host
defenses, and toxin production
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