Question 1

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

Accepted Answer

A primary pathogen is a microbe that is able to cause disease in an otherwise healthy individual, meaning that it can cause disease even in a person with a normal immune system. Examples include Streptococcus pyogenes, which causes strep throat, and Mycobacterium tuberculosis, which causes tuberculosis. In contrast, an opportunistic pathogen only causes disease when introduced into an unusual location (such as the urinary tract) or when infecting an immunocompromised host (such as a person with HIV/AIDS or undergoing chemotherapy). Examples include Pneumocystis jirovecii, which causes pneumonia in immunocompromised individuals, and Candida albicans, which can cause infections in the mouth, vagina, and other areas in people with weakened immune systems.

Question 2

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

Accepted Answer

The normal gastrointestinal microbiota plays a 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. Option A is only one of the ways in which the microbiota prevents colonization by pathogens; option B is also partially correct, but it does not include the fact that the microbiota produces toxic compounds; option C is incorrect because the microbiota does not phagocytize incoming pathogens; and option E is not entirely accurate, as there are no known carbohydrate "traps" that are secreted by the microbiota.

Question 3

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

Accepted Answer

The length of the incubation period is influenced by multiple factors, including the number of infectious cells or virions encountered, the host's condition, and the growth rate of the pathogen. Environmental conditions and the carrier's vaccination status may also play a role, but are not the only determining factors. Therefore, option D is the most accurate choice.

Question 4

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.

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 5

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?

Accepted Answer

Boiling home-canned foods before consumption helps prevent botulism because it would denature the botulism exotoxin and inactivate it. The exotoxin is what leads to the disease symptoms, so this would make the food safer. Boiling does not destroy endospores, but it does destroy vegetative cells. Weakening endospores and removing odor are not effective methods for preventing botulism.

Question 6

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

Accepted Answer

Koch's postulates require the ability to grow the pathogen in pure culture, which is not possible for Treponema pallidum.

Question 7

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

Accepted Answer

If the receptor is critical for the cell, the cell has no choice but to put it out there. This makes it a good strategy for the microbe as it increases its chances of infecting the host cell.

Question 8

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?

Accepted Answer

If there is a contaminating microbe present but the original suspect microbe is still present, and the disease still manifests in test animals and the organism is still recoverable, then there is no consequence to using a contaminated culture.

Question 9

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

Accepted Answer

The incubation period is the time between exposure to an agent and the onset of disease signs and symptoms. During this time, the agent is multiplying within the body and the immune system is mounting a response. Once the incubation period has ended, the prodromal phase begins and symptoms start to appear. The decline phase is the period during which the symptoms of the disease gradually lessen and the person begins to recover. The lag phase is the period in which the agent is introduced into the body and begins to multiply, but no symptoms are yet present. The carrier phase refers to a person who is infected with an agent and able to transmit it to others, but does not display symptoms of the disease themselves.

Question 10

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

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 11

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

Accepted Answer

The statement "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" does not directly relate to the increasing frequency of opportunistic infections, as opportunistic infections usually occur in individuals with impaired immune systems.

Question 12

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

Accepted Answer

Dysbiosis refers to an imbalance in the microbiome, which can be caused by factors such as antibiotic use, diet, or environmental exposure. It can lead to a variety of health problems, including inflammation, infection, and disease. Immunocompetence (A) is the ability of the immune system to respond effectively to pathogens. Parasitism (B) is a type of symbiotic relationship in which one organism benefits at the expense of the other. Secondary infection (D) refers to an infection that occurs after the initial infection has already been established. Fc receptors (E) are molecules found on the surface of immune cells that help to bind and eliminate pathogens.

Question 13

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

Accepted Answer

Viruses do not produce enzymes that make holes in the phagocyte membrane. This statement is false.

Question 14

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

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 15

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?

Accepted Answer

Not all pathogens inject molecules into host cells using injectisomes. Some pathogens use other mechanisms such as adhesins or toxins.

Question 16

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?

Accepted Answer

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.

Question 17

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

Accepted Answer

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

Question 18

Please select the correct definition of balanced pathogenicity.

Accepted Answer

Balanced pathogenicity refers to a host-parasite relationship in which the parasite persists in the host while causing minimal harm. In this scenario, the pathogen becomes less virulent while the host becomes less susceptible, leading to a balanced state. Thus, option E is the correct definition of balanced pathogenicity.

Question 19

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

Accepted Answer

The B subunit of an A-B toxin is responsible for binding to target cells. If antibodies bind to the B portion, the toxin can no longer bind to target cells and will thus not affect those cells.

Question 20

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

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.

Quiz 16: Host-Microbe Interactions