Question 1

Please select the CORRECT definition regarding interactions between hosts and microbes.
A) Immunocompetent-having a weakness or defect in the innate or adaptive defenses.
B) Parasitism-relationship between two organisms in which one partner benefits and the other is unaffected.
C) Dysbiosis-an imbalance in the microbiome that may be caused by taking antimicrobial medications.
D) Secondary infection-infection in a previously healthy person, such as measles in a child who has not had measles before.
E) Fc receptors-molecule that binds the antigen-binding region of an antibody.

Accepted Answer

Dysbiosis refers to an imbalance in the microbiome that can occur due to various factors, including taking antimicrobial medications, and can lead to negative interactions between hosts and their microbial communities.

Answer: B
 Parasitism is a type of symbiotic relationship between two organisms in which one partner (the parasite) benefits and the other is harmed (the host). This is not specific to interactions between hosts and microbes, but can include various types of organisms.

The other answer choices are incorrect:
A) Immunocompetent refers to having a fully functional immune system, rather than a weakened one.
D) Secondary infection refers to an infection that occurs after a primary infection has already occurred, rather than a specific interaction between hosts and microbes.
E) Fc receptors are molecules on immune cells that bind to the Fc region of antibodies, allowing for various immune functions. While this is related to host-microbe interactions, it is a specific component of the immune response rather than an overarching concept.

Question 2

In two of Koch's postulates (#2 and #3), a pure culture of the organism is required. Which of the following would NOT be a possible consequence of using a contaminated culture?
A) You can't necessarily attribute the illness directly to the microbe in question; it may in fact be caused by the contaminating microbe.
B) There's the possibility that the test animal might be acutely susceptible to the contaminating microbe, but completely resistant to the microbe you suspect causes the illness of interest. As such, when you introduce it into the test animal, it could confuse your final results.
C) Even though there's a contaminating microbe present, as long as the original suspect microbe is also present, the disease should still manifest in test animals and the organism should still be recoverable from test animals. As such, there's really no consequence to using a contaminated culture.
D) The problem is that one microbe may be toxic to the other. It may have killed all of your suspect microbe in the culture. Therefore, you can't be sure that you're infecting your test animals with the microbe you suspect is causing the illness, or if it's only the second (contaminating) microbe.
E) These would all be consequences of using contaminated cultures.

Accepted Answer

Choice C is incorrect because if there's a contaminating microbe present, it may outcompete the suspect microbe and mask the disease, making it impossible to recover the suspect microbe from test animals. The other choices are possible consequences of using a contaminated culture.

Question 3

Which of the following is NOT a likely reason why diseases caused by opportunists are becoming more frequent in the U.S. population? 
A) People with impaired immune systems such as those with HIV disease survive longer due to more effective therapies, but this gives them a longer period of time to be infected by opportunists.
B) People in the U.S. are living longer than ever before, but they're living with a number of chronic health issues that can impair the immune system. This leads to a greater likelihood of opportunistic infections.
C) Cancer treatments have improved significantly in the last 30 years, but they often suppress the immune system. This leads to a greater likelihood of opportunistic infections in people receiving these treatments.
D) Travel into and out of the U.S. has increased significantly. This has the potential to bring in many new pathogens that can cause infections, even in otherwise healthy and immunocompetent individuals.
E) People in the U.S. are living longer than ever before, but their immune systems decline with age. This leads to a greater likelihood of opportunistic infections, especially if they receive any kind of invasive procedure.

Accepted Answer

The correct answer is D because it describes the introduction of new pathogens affecting healthy individuals, which does not specifically relate to the increase in diseases caused by opportunists. Opportunistic infections typically occur in individuals with weakened immune systems, not in healthy, immunocompetent individuals.

Question 4

Why is it not possible to use Koch's postulates to show that Treponema pallidum causes syphilis?
A) T. pallidum is a Gram-negative organism.
B) T. pallidum cannot be grown in pure culture.
C) T. pallidum causes different diseases in different hosts.
D) Syphilis is a polymicrobial disease; T. pallidum is only one of the causative agents involved in the disease.
E) T. pallidum does not contain a genome.

Accepted Answer

Koch's postulates require the ability to culture the pathogen in pure culture, which is not possible with T. pallidum.

Question 5

Please select the correct definition of balanced pathogenicity.
A) A host-parasite relationship in which the parasite persists in the host, causing maximal harm. The pathogen becomes more virulent while the host becomes increasingly susceptible.
B) A generated balance in the microbiome that may be caused by taking antimicrobial medications. It generally helps the host maintain optimal health.
C) A mechanism that allows bacteria to transfer gene products directly into host cells, inducing changes such as altering the cell's cytoskeleton structure.
D) A situation in which an abnormally high number of TH cells (effector helper T cells) are stimulated, causing a massive release of cytokines (a "cytokine storm").
E) A host-parasite relationship in which the parasite persists in the host while causing minimal harm. The pathogen becomes less virulent while the host becomes less susceptible.

Accepted Answer

Balanced pathogenicity refers to a host-parasite relationship in which the parasite is able to persist in the host without causing significant harm. This is achieved through a decrease in virulence of the pathogen and/or a decrease in susceptibility of the host. Option E is the only choice that accurately describes balanced pathogenicity.

Question 6

A number of viruses often include a similar set of symptoms when they cause an infectious disease state (fever, headache, fatigue, runny nose). Why would they all cause the same symptoms if they're different viruses?
A) They all possess the same basic virulence genes and molecules, so they all trigger the same responses.
B) The symptoms are associated with the immune system's response, NOT the molecules from the pathogens themselves. Our responses against viruses are fairly similar, regardless of virus type, so the symptoms are similar.
C) Most viruses infect the upper respiratory tract. This leads to the common set of symptoms listed above. Only a few viruses infect areas away from this region.
D) Viruses specifically infect mainly epithelial membranes. As such, the virally induced reaction is similar in different areas of the body due to the same basic cell types (epithelial cells) being infected in each area.
E) All animal viruses must attach to and enter host cells. Since this step in the life cycle is identical in all viruses, the signs and symptoms that follow will also be identical.

Accepted Answer

The symptoms are a response generated by the host immune system, not the molecules specific to the virus itself. Therefore, similar symptoms may be seen in response to different viruses because the immune response to viral infections is relatively consistent.

Question 7

Jay tells you that he ate chicken for dinner, which you suspect is the source of his infection. You tell Jay that infectious disease progresses through several stages, and that he is in the 
A) incubation period.
B) prodromal period.
C) illness phase.
D) recovery phase.
E) convalescence stage.

Accepted Answer

The illness phase is the period during which the signs and symptoms of an infectious disease are most prominent and severe, indicating that the infection is actively affecting the body. Since Jay is showing symptoms that led to the suspicion of an infection (implied by the context), he is in the illness phase.

Question 8

Select the correct sequence for proving Koch's postulates.
1) The microorganism must be recovered from the experimentally infected hosts.
2) The microorganism must be present in every case of the disease.
3) The same disease must be produced when a pure culture of the microorganism is introduced into susceptible hosts.
4) The microorganism must be grown in pure culture from diseased hosts.
A) 2, 4, 3, 1
B) 1, 2, 3, 4
C) 1, 3, 2, 4
D) 4, 3, 1, 2
E) 4, 1, 2, 3

Accepted Answer

Koch's postulates are a series of criteria established by Robert Koch to identify the causative agent of a particular disease. These steps are: 1) The microorganism must be present in every case of the disease. 2) The microorganism must be grown in pure culture from diseased hosts. 3) The same disease must be produced when a pure culture of the microorganism is introduced into susceptible hosts. 4) The microorganism must be recovered from the experimentally infected hosts. Therefore, the correct sequence is 2, 4, 3, 1.

Question 9

You think that Jay may have a Salmonella infection. Although a person's normal gastrointestinal microbiota protects them from pathogenic infections, in this case, Jay has contracted the disease. You explain to Jay the role his normal microbiota plays in excluding pathogens, including
A) covering binding sites that might otherwise be used for attachment by a pathogen
B) consuming available nutrients (thus "starving") the pathogen AND reducing water and oxygen availability in their immediate environment
C) producing compounds toxic to other bacteria AND phagocytizing any incoming pathogenic cells
D) producing compounds toxic to other bacteria, consuming available nutrients (thus "starving" the pathogen) AND covering binding sites that might otherwise be used for attachment by a pathogen.
E) producing compounds toxic to other bacteria, secreting carbohydrate "traps" that catch foreign bacteria AND phagocytizing any incoming pathogenic cells

Accepted Answer

The normal microbiota plays a crucial role in excluding pathogens by producing compounds toxic to other bacteria, consuming available nutrients (thus "starving" the pathogen), and covering binding sites that might otherwise be used for attachment by a pathogen. Choices A, B, C, and E all describe individual mechanisms by which the microbiota may exclude pathogens but do not encompass all the ways in which this may occur.

Question 10

Is it a good strategy for a microbe to adhere to a receptor that plays a critical function for a host cell?
A) No, it ISN'T a good strategy. Host cells could use an alternative receptor and shut down production of the main receptor. The microbe would not have anything to attach to and the cell would thus prevent infection.
B) Yes, it IS a good strategy. If it's a receptor the cell MUST use, it doesn't have an alternative receptor to switch to, so even though that receptor makes the cell susceptible to infection, it HAS to put that target out there. This benefits the microbe.
C) No, it ISN'T a good strategy. Microbes need to evade detection and elimination by the immune system. If they adhere to a receptor that plays a critical function, they are less likely to trigger destructive immune responses. This would be similar to using a hostage as a shield in a police-standoff situation.
D) No, it ISN'T a good strategy. By binding to receptors, the microbes will be phagocytosed by cells and destroyed within them, thus failing to infect the host cell.
E) Yes, it IS a good strategy. If the microbe attaches to a critical receptor, the host cell will be forced to try to rid itself of the pathogen. One way it can do this is to phagocytose the pathogen, thereby taking it into its own nucleus, which benefits the pathogen.

Accepted Answer

If the receptor plays a critical function for the host cell and there are no alternative receptors, the host cell has no choice but to express it, making the host cell more susceptible to infection. This benefits the microbe.

Question 11

Please select the False statement regarding viral avoidance of the immune response.
A) Some viruses interfere with antigen presentation by MHC class I molecules.
B) Some viruses produce enzymes that, when activated, make holes in the phagocyte membrane, killing the cell.
C) Some viruses move directly from one cell to its immediate neighbors, thus avoiding antibodies.
D) Some viruses encode proteins that shut down expression of host genes such as those encoding IFNs and AVPs.
E) Some viruses display "fake" MHC class I molecules, tricking the immune system into believing that the cell is uninfected.

Accepted Answer

While some viruses do interfere with antigen presentation, shut down host genes, display fake MHC molecules, and move directly from cell to cell, no viruses produce enzymes that make holes in the phagocyte (immune cell) membrane themselves. It is possible for bacteria to produce such enzymes, but not viruses.

Question 12

Which of the following is NOT a mechanism for avoiding destruction by a phagocyte?
A) Some pathogens escape from the phagosome before it fuses with lysosomes.
B) Some pathogens prevent phagosome-lysosome fusion.
C) Some microbes can survive the destructive environment within the phagolysosome.
D) Some microbes produce IgA protease that cleaves IgA, the class of antibody found in mucus and other secretions.
E) These are all mechanisms for avoiding phagocytic destruction.

Accepted Answer

Option D describes a mechanism by which some microbes evade the immune system by cleaving IgA, an antibody involved in mucosal immunity, rather than directly avoiding destruction by phagocytes. Options A, B, and C all describe mechanisms by which pathogens can avoid destruction by phagocytes, making D the correct choice as it does not.

Question 13

Home-canned foods should be boiled before consumption to prevent botulism. Considering that this treatment does NOT destroy endospores, why would it be helpful in preventing the disease?
A) Because it would destroy the vegetative cells, and only the vegetative cells cause the disease.
B) Because it would at least weaken the endospores, making them more susceptible to elimination by our immune system.
C) Because the heat would denature the botulism endotoxin and inactivate it. The endotoxin is what leads to the disease symptoms, so this would make the food safer.
D) Because although botulism exotoxin is harmless, it has a bad odor and boiling removes this, making the food more appealing to eat.
E) Because the heat would denature the botulism exotoxin and inactivate it. The exotoxin is what leads to the disease symptoms, so this would make the food safer.

Accepted Answer

Boiling home-canned foods before consumption is helpful in preventing botulism because the heat would denature the botulism exotoxin and inactivate it. The exotoxin is what leads to the disease symptoms, so this would make the food safer. It does not necessarily destroy endospores, but it renders the exotoxin harmless.

Question 14

What is the difference between a primary pathogen and an opportunistic pathogen?
A) A primary pathogen is a microbe that is able to cause disease in an otherwise healthy individual, while an opportunistic pathogen is a microbe that causes disease only when introduced into an unusual location or into an immunocompromised host.
B) An opportunistic pathogen is a microbe that is able to cause disease in an otherwise healthy individual, while a primary pathogen is a microbe that causes disease only when introduced into an unusual location or into an immunocompromised host.
C) A primary pathogen is an environmental microbe that is able to cause disease in an otherwise healthy individual, while an opportunistic pathogen is always a member of the normal microbiota and causes disease only when introduced into an unusual location.
D) A primary pathogen is an environmental microbe that is able to cause disease in an otherwise healthy individual, while an opportunistic pathogen is always a member of the normal microbiota and only causes disease in an immunocompromised host.
E) A primary pathogen is a microbe that is able to cause disease in an otherwise healthy individual, while opportunistic pathogens are the microorganisms routinely found growing in and on the body of a healthy individual.

Accepted Answer

A primary pathogen is a microbe that is able to cause disease in an otherwise healthy individual, while an opportunistic pathogen is a microbe that causes disease only when introduced into an unusual location or into an immunocompromised host. This means that primary pathogens are inherently more virulent and have specific mechanisms to infect and cause disease in healthy hosts, whereas opportunistic pathogens take advantage of weakened host defenses or unusual environmental conditions to cause disease.

Question 15

The period of time between exposure to an agent and the onset of disease signs and symptoms is called the
A) prodromal phase.
B) decline phase.
C) incubation period.
D) lag phase.
E) carrier phase.

Accepted Answer

The incubation period is the time between exposure to an agent and the onset of disease signs and symptoms. During this period, the agent is replicating and/or growing within the host but has not yet caused any noticeable symptoms.

Question 16

Select the INCORRECT definition regarding the progression of an infectious disease.
A) Illness phase-period of time during which symptoms and signs of disease occur.
B) Incubation period-interval between the entrance of a pathogen into a susceptible host and the onset of illness caused by that pathogen.
C) Prodromal period-a period of early, vague symptoms indicating the onset of a disease.
D) Period of convalescence-period of recuperation and recovery from an illness.
E) Carrier phase-period in which a pathogen is harbored without noticeable ill effects, but may be transmitted to other hosts.

Accepted Answer

The carrier phase is incorrectly defined as it implies no noticeable ill effects on the host, which is not always true. Carriers can sometimes exhibit mild symptoms or be asymptomatic, but the key aspect is their ability to transmit the pathogen to others, not the absence of all symptoms.

Question 17

The length of the incubation period depends on a variety of factors, including
A) the growth rate of the pathogen AND environmental conditions.
B) the host's condition AND the carrier's vaccination status.
C) number of infectious cells or virions encountered AND the host's condition.
D) number of infectious cells or virions encountered, the host's condition, AND the growth rate of the pathogen.
E) the growth rate of the pathogen only.

Accepted Answer

The length of the incubation period is influenced by a combination of factors, including the number of infectious cells or virions encountered, the host's immune system status, and the growth rate of the pathogen. Environmental conditions and carrier vaccination status may also play a role. Therefore, option D which includes all the factors mentioned above is the best choice.

Question 18

You explain to Jay that infections and the associated diseases are often described according to the timing and duration of the symptoms. You define the different categories to him, telling him that he has
A) a chronic infection, which is an infection that develops slowly and may last for months or years.
B) a latent infection-the microbe causing Jay's illness will continue to exist in him, although likely without causing any symptoms.
C) a localized infection, in which the microbe is limited to a small area-in Jay's case the gastrointestinal tract.
D) an inopportunistic infection, because Salmonella species are part of a person's gastrointestinal normal microbiota.
E) an acute infection, characterized by symptoms that develop quickly but last only a short time.

Accepted Answer

Jay has an acute infection as his symptoms developed quickly but are expected to last only a short time.

Question 19

You describe to Jay the initial events that must have occurred in order for him to become ill. Which of the following statements is False? 
A) All pathogens must inject molecules into the host cell that induce a specific change in those cells; this is performed via structures called injectisomes.
B) Following adhesion, the pathogen must colonize the host, growing on the host cell surface.
C) Pathogens must adhere to host cells to initiate infection; bacteria use adhesins to attach to receptors on host cells.
D) In order to colonize, a pathogen must often compete with the normal microbiota, prevent binding of secretory IgA, and obtain iron.
E) All of these statements are correct.

Accepted Answer

Not all pathogens use injectisomes to induce a specific change in the host cells. Some pathogens may use other mechanisms such as secretion systems.

Question 20

Would an antibody response against the B subunit of an A-B toxin protect against the effects of the toxin?
A) Yes. If antibodies bind to the B portion, the toxin can no longer bind to target cells and will thus not affect those cells.
B) No. Even if antibodies bind to the B portion of the toxin, it is the A portion that actually causes damage to the cell.
C) Yes. If antibodies bind to the B portion, that portion of the toxin does not become activated, and thus does not damage the host cell.
D) No. Even if antibodies bind to the B portion of the toxin, the toxin is still taken into the host cell by phagocytosis, damaging that cell.
E) This question cannot be answered. The immune system does not mount a strong response against proteins, so this situation is unlikely to occur.

Accepted Answer

Antibodies binding to the B subunit of an A-B toxin would prevent the toxin from binding to target cells and thus protect against the effects of the toxin. This is because the B subunit is responsible for binding to host cells, while the A subunit is responsible for the toxic effects once inside the cell. By preventing the B subunit from binding, the A subunit cannot enter the cell and cause damage.

Quiz 16: Host-Microbe Interactions

Please select the CORRECT definition regarding interactions between hosts and microbes.

In two of Koch's postulates (#2 and #3) , a pure culture of the organism is required. Which of the following would NOT be a possible consequence of using a contaminated culture?

Which of the following is NOT a likely reason why diseases caused by opportunists are becoming more frequent in the U.S. population?

Why is it not possible to use Koch's postulates to show that Treponema pallidum causes syphilis?

Please select the correct definition of balanced pathogenicity.

A number of viruses often include a similar set of symptoms when they cause an infectious disease state (fever, headache, fatigue, runny nose) . Why would they all cause the same symptoms if they're different viruses?

Jay tells you that he ate chicken for dinner, which you suspect is the source of his infection. You tell Jay that infectious disease progresses through several stages, and that he is in the

You think that Jay may have a Salmonella infection. Although a person's normal gastrointestinal microbiota protects them from pathogenic infections, in this case, Jay has contracted the disease. You explain to Jay the role his normal microbiota plays in excluding pathogens, including

Is it a good strategy for a microbe to adhere to a receptor that plays a critical function for a host cell?

Please select the False statement regarding viral avoidance of the immune response.

Which of the following is NOT a mechanism for avoiding destruction by a phagocyte?

Home-canned foods should be boiled before consumption to prevent botulism. Considering that this treatment does NOT destroy endospores, why would it be helpful in preventing the disease?

What is the difference between a primary pathogen and an opportunistic pathogen?

The period of time between exposure to an agent and the onset of disease signs and symptoms is called the

Select the INCORRECT definition regarding the progression of an infectious disease.

The length of the incubation period depends on a variety of factors, including

You explain to Jay that infections and the associated diseases are often described according to the timing and duration of the symptoms. You define the different categories to him, telling him that he has

You describe to Jay the initial events that must have occurred in order for him to become ill. Which of the following statements is False?

Would an antibody response against the B subunit of an A-B toxin protect against the effects of the toxin?