Micro Dr Sloma Questions

1. Which of the following describes negative selection of immature B cells?

B cells that receive signals through the preB cell receptor survive and continue development.

B cells that can adequately recognize foreign antigen are signaled to continue development.

B cells that can adequately recognize self antigen are signaled to continue development

B cells that recognize self antigen are signaled to die by apoptosis.

Negative selection of immature B cells refers to the process where B cells that recognize self antigens are eliminated or signaled to undergo programmed cell death (apoptosis). This is an important mechanism to prevent the development of B cells that could potentially attack the body's own tissues (autoimmunity). By eliminating self-reactive B cells, the immune system ensures that only B cells capable of recognizing foreign antigens are allowed to mature and participate in immune responses.

Explanation

Negative selection of immature B cells refers to the process where B cells that recognize self antigens are eliminated or signaled to undergo programmed cell death (apoptosis). This is an important mechanism to prevent the development of B cells that could potentially attack the body's own tissues (autoimmunity). By eliminating self-reactive B cells, the immune system ensures that only B cells capable of recognizing foreign antigens are allowed to mature and participate in immune responses.

2. What do Rickettsia sp., Coxiella sp., and Chalmydia sp. have in common?

All have periplasmic flagella

All are fastidious and have special requirements for growth in culture

Infection with these organisms is usually associated with contact with animals

They are all oxidase negative and ferment glucose

All have an obligate requirement for growth within host cells

They are all transmitted by arthropods

Rickettsia sp., Coxiella sp., and Chlamydia sp. all have an obligate requirement for growth within host cells. This means that they cannot grow and replicate outside of a host cell and are dependent on the host cell's machinery for their survival and reproduction.

Explanation

Rickettsia sp., Coxiella sp., and Chlamydia sp. all have an obligate requirement for growth within host cells. This means that they cannot grow and replicate outside of a host cell and are dependent on the host cell's machinery for their survival and reproduction.

3. Which of the following best describes the mechanism behind β‐hemolysis, resulting in the complete clearing of the media around a colony growing on blood agar?

Hemolysis is caused by the coagulase enzyme which is converting fibrinogen in the media to fibrin

Cytochrome c oxidase produced by the organism oxidizes the hemoglobin in the media

The organism uses the hemoglobin as a source of energy, causing clearing of the media

The catalase enzyme produced by the organism oxidizes the hemoglobin in the media

The organism produces a hemolysin which completely lyses the red blood cells in the media

β-hemolysis refers to the complete lysis of red blood cells in the media. This is caused by the organism producing a hemolysin, which is a toxin that specifically targets and lyses red blood cells. As a result, the media around the colony appears clear because the red blood cells have been completely lysed.

Explanation

β-hemolysis refers to the complete lysis of red blood cells in the media. This is caused by the organism producing a hemolysin, which is a toxin that specifically targets and lyses red blood cells. As a result, the media around the colony appears clear because the red blood cells have been completely lysed.

4. You are awaiting results of a throat culture from your patient, a 7‐year old girl. You call the lab for a preliminary report. The lab technologist tells you that the culture is positive for Gram+ cocci in chains, Gram‐positive bacilli, and Gram‐negative cocci. The technologist adds, "I'm going to subculture the Gram‐positive rod to a tellurite agar today." Growth of the Gram‐positive rod on tellurite would indicate the organism is which of the following?

Neisseria meningitidis

Streptococcus pneumoniae

Corynebacterium diphtheriae

Leginonella pneumophila

Actinomyces isrealii

Staphyloccus aureus

The growth of the Gram-positive rod on tellurite agar indicates that the organism is Corynebacterium diphtheriae. This is because Corynebacterium diphtheriae is the only organism among the options that is known to produce tellurite reductase, an enzyme that allows it to reduce tellurite and grow on tellurite agar. This characteristic is used as a diagnostic test for identifying Corynebacterium diphtheriae.

Explanation

The growth of the Gram-positive rod on tellurite agar indicates that the organism is Corynebacterium diphtheriae. This is because Corynebacterium diphtheriae is the only organism among the options that is known to produce tellurite reductase, an enzyme that allows it to reduce tellurite and grow on tellurite agar. This characteristic is used as a diagnostic test for identifying Corynebacterium diphtheriae.

5. Th2 T cells exert their effector functions through which of the following mechanisms?

Secretion of IL‐4 and IL‐5

Engulfment of osponized antigen

Secretion of cytolytic molecules

Expression of CD28

Recognition of cells that lack MHC class I expression

Th2 T cells exert their effector functions through the secretion of IL-4 and IL-5. These cytokines play a crucial role in the activation and recruitment of other immune cells, particularly B cells and eosinophils. IL-4 promotes the differentiation of B cells into antibody-producing plasma cells, while IL-5 stimulates the production and activation of eosinophils, which are involved in the defense against parasitic infections and allergic reactions. Therefore, the secretion of IL-4 and IL-5 by Th2 T cells is essential for the immune response against certain pathogens and the regulation of allergic responses.

Explanation

Th2 T cells exert their effector functions through the secretion of IL-4 and IL-5. These cytokines play a crucial role in the activation and recruitment of other immune cells, particularly B cells and eosinophils. IL-4 promotes the differentiation of B cells into antibody-producing plasma cells, while IL-5 stimulates the production and activation of eosinophils, which are involved in the defense against parasitic infections and allergic reactions. Therefore, the secretion of IL-4 and IL-5 by Th2 T cells is essential for the immune response against certain pathogens and the regulation of allergic responses.

6. The difference between chocolate agar and blood agar is:

The two agars contain different carbohydrates and the two agars are used to test for differentcarbohydrate utilization patterns.

Chocolate agar contains charcoal to absorb inhibitory substances produced by different organisms.

Chocolate agar contains specific dyes used to inhibit the growth of Gram‐positive organisms

The blood used in chocolate agar has been heated.

Chocolate agar contains cacao, instead of sheep blood, as a nutrient source

The correct answer is "The blood used in chocolate agar has been heated." This is because chocolate agar is made by heating sheep blood to inactivate certain enzymes that could interfere with the growth of bacteria. Heating the blood also helps release nutrients that are essential for bacterial growth. This process is important in creating a suitable environment for bacterial culture and identification in the laboratory.

Explanation

The correct answer is "The blood used in chocolate agar has been heated." This is because chocolate agar is made by heating sheep blood to inactivate certain enzymes that could interfere with the growth of bacteria. Heating the blood also helps release nutrients that are essential for bacterial growth. This process is important in creating a suitable environment for bacterial culture and identification in the laboratory.

7. Blood cultures were collected from a patient and cultured under aerobic conditions. After 48 hours, the cultures were positive, and a Gram stain of the culture revealed large, spore‐forming Gram‐positive bacilli. Which of the following describes the organisms growing in this patient's blood culture?

A saprophytic organisms found in the soil or intestinal tract of humans and animals

Obligate intracellular organisms

Branching, filamentous rods

Can be club‐shaped or can resemble Chinese letters

Have a cell wall similar to that of mycobateria

The correct answer describes the organisms growing in the patient's blood culture as saprophytic organisms found in the soil or intestinal tract of humans and animals. This suggests that the organisms are likely to be normal flora or opportunistic pathogens that have entered the bloodstream.

Explanation

The correct answer describes the organisms growing in the patient's blood culture as saprophytic organisms found in the soil or intestinal tract of humans and animals. This suggests that the organisms are likely to be normal flora or opportunistic pathogens that have entered the bloodstream.

8. You are awaiting results of a throat culture from your patient, a 7‐year old girl. You call the lab for a preliminary report. The lab technologist tells you that the culture is positive for Gram+ cocci in chains, Gram‐positive bacilli, and Gram‐negative cocci. Which of the following organisms could be growing in her specimen?

Staphylococcus spp,. Brucella spp., and Actinomyces spp.

Neisseria spp., Streptococcus spp., and Corynebacterium spp.

Pseudomonas spp., Mycobateria spp., and Neisseria spp.

Staphylococcus sp., Neisseria sp., and Legionella sp.

The presence of Gram+ cocci in chains suggests the presence of Streptococcus spp. The presence of Gram‐positive bacilli suggests the presence of Corynebacterium spp. The presence of Gram‐negative cocci suggests the presence of Neisseria spp. Therefore, Neisseria spp., Streptococcus spp., and Corynebacterium spp. could be growing in her specimen.

Explanation

The presence of Gram+ cocci in chains suggests the presence of Streptococcus spp. The presence of Gram‐positive bacilli suggests the presence of Corynebacterium spp. The presence of Gram‐negative cocci suggests the presence of Neisseria spp. Therefore, Neisseria spp., Streptococcus spp., and Corynebacterium spp. could be growing in her specimen.

9. A 45‐year old woman presents with a rashy skin lesion. She takes daily walks with her dogs in the woods and recalls having removed a tick from her back 3 days ago. A Gram‐stain of a biopsy of the lesion is negative. You suspect she is infected with Borrelia sp. Which of the following statements is most accurate regarding Borrelia sp.?

The Gram‐stain of her biopsy would most likely reveal the organism in or associated withpolymorphonculear cells.

The dog is more likely than the tick to have been the vector

To isolate the organism, tissue from the biopsy should be cultured using cell lines

The organism is better visualized using dark field microscopy instead of a Gram stain

To isolate the organism, cultures should be incubated at 42°C under microaerophilic conditions

Dark field microscopy is a technique that allows for the visualization of organisms that are difficult to see using traditional bright field microscopy. Borrelia sp., the bacteria responsible for Lyme disease, is a spirochete that is better visualized using dark field microscopy due to its thin, helical shape. This technique allows for the visualization of the organism's characteristic motility and helps in the identification of Borrelia sp. Therefore, dark field microscopy is a more accurate method for visualizing Borrelia sp. compared to a Gram stain.

Explanation

Dark field microscopy is a technique that allows for the visualization of organisms that are difficult to see using traditional bright field microscopy. Borrelia sp., the bacteria responsible for Lyme disease, is a spirochete that is better visualized using dark field microscopy due to its thin, helical shape. This technique allows for the visualization of the organism's characteristic motility and helps in the identification of Borrelia sp. Therefore, dark field microscopy is a more accurate method for visualizing Borrelia sp. compared to a Gram stain.

10. Positive selection is an important step in T cell development. Which of the following best describes this process?

Immature T cells with receptors that associate with self MHC with adequate affinity are selected tomature.

Immature T cells with receptors that recognize self antigens are signaled to die by apoptosis.

Immature T cells with receptors that recognize self MHC with too high or too low affinity for self MHCare signaled to die by apoptosis.

Signals through the preT cell receptor tell the developing T cell to survive.

Developing T cells that rearrange the gamma and delta receptor genes will commit to gamma‐delta Tcell lineage.

During T cell development, immature T cells with receptors that associate with self major histocompatibility complex (MHC) with adequate affinity are selected to mature. This selection process ensures that T cells are able to recognize and respond to antigens presented by self MHC molecules. T cells that do not have receptors that associate with self MHC or have receptors with too high or too low affinity for self MHC are signaled to undergo apoptosis, preventing the development of T cells that may cause autoimmune reactions. This process is crucial for the proper functioning of the immune system.

Explanation

During T cell development, immature T cells with receptors that associate with self major histocompatibility complex (MHC) with adequate affinity are selected to mature. This selection process ensures that T cells are able to recognize and respond to antigens presented by self MHC molecules. T cells that do not have receptors that associate with self MHC or have receptors with too high or too low affinity for self MHC are signaled to undergo apoptosis, preventing the development of T cells that may cause autoimmune reactions. This process is crucial for the proper functioning of the immune system.

11. In addition to recognition of specific peptide presented by MHC, T cells require other signals to drive activation, proliferation and differentiation. What are these other signals?

CD40:CD40L and IL‐4

CD40:CD40L and IL‐2

CD28:B7 and IL‐4

CD28:B7 and IL‐2

T cells require CD28:B7 co-stimulation and IL-2 cytokine signaling in addition to the recognition of specific peptides presented by MHC in order to undergo activation, proliferation, and differentiation. CD28:B7 interaction provides a co-stimulatory signal that enhances T cell activation, while IL-2 is a crucial cytokine that promotes T cell proliferation and survival. Therefore, both CD28:B7 co-stimulation and IL-2 cytokine signaling are necessary for T cell activation and subsequent immune response.

Explanation

T cells require CD28:B7 co-stimulation and IL-2 cytokine signaling in addition to the recognition of specific peptides presented by MHC in order to undergo activation, proliferation, and differentiation. CD28:B7 interaction provides a co-stimulatory signal that enhances T cell activation, while IL-2 is a crucial cytokine that promotes T cell proliferation and survival. Therefore, both CD28:B7 co-stimulation and IL-2 cytokine signaling are necessary for T cell activation and subsequent immune response.

12. Asad is a 25‐year old HIV‐positive man. He returned from visiting relatives in Somalia 3 months ago. For the last 2 months, he has been experiencing fevers, night sweats, weight loss and a dry cough. Within the last two weeks his cough has become productive of bloody sputum. His chest x‐ray is remarkable for bilateral anterior cervical and axillary adenopathy with interstitial infiltrates. A smear of his sputum is positive for acid fast bacilli. The causative agent of this infection was able to establish active infection due the failure to generate which of the following?

IgM antibodies

IgG antibodies

IgE antibodies

Th1 T cells

Th17 T cells

The causative agent of the infection was able to establish active infection due to the failure to generate Th1 T cells. Th1 T cells play a crucial role in cell-mediated immunity and are responsible for activating macrophages to kill intracellular pathogens, such as Mycobacterium tuberculosis (the causative agent of tuberculosis). Without Th1 T cell activation, the immune response is impaired, allowing the infection to persist and cause symptoms such as fevers, night sweats, weight loss, and a productive cough with bloody sputum.

Explanation

The causative agent of the infection was able to establish active infection due to the failure to generate Th1 T cells. Th1 T cells play a crucial role in cell-mediated immunity and are responsible for activating macrophages to kill intracellular pathogens, such as Mycobacterium tuberculosis (the causative agent of tuberculosis). Without Th1 T cell activation, the immune response is impaired, allowing the infection to persist and cause symptoms such as fevers, night sweats, weight loss, and a productive cough with bloody sputum.

13. A 30‐year old man presents to his local emergency department with symptoms of sepsis. His blood cultures flag positive for Gram‐positive cocci in clusters. As the laboratory technologist, which of the following describes the test(s) that will be most conclusive for confirming his infection is caused by Staphylococcus aureus? I) Observation of β‐hemolysis on blood agar II) Test for the production an enzyme that converts fibrinogen to fibrin III) Test for the organism's ability to ferment glucose IV) Test for the production of an enzyme that converts H2O2 to O2 and water V) Test for the organism's ability to grow at low temperatures VI) Test for the production of cytochrome c oxidase

I only

II only

I and II

III and VI

II and IV

V only

IV only

Explanation

14. Organism Z causes over 1 million causes of Z fever annually worldwide. Scientists have determined that a live, attenuated vaccine is most appropriate for this organism. What type of organism is Organism Z likely to be?

An intracellular bacterium

An extracellular bacterium that mediates tissue destruction via toxin production

A virus that causes cervical cancer

A virus that establishes latency within leukocytes

A helminth

Vaccines containing killed pathogens or antigenic components (subunits like peptides) do not enter host cells. Hence, they induce a B cell-mediated humoral response. On the other hand, live ATTENUATED LIVE VACCINES do penetrate cells, eliciting a cell-mediated immune response against intracellular antigens. SO FOR INTRACELLULAR ORGANISMS, LIVE ATTENUATED VACCINES ARE MORE EFFECTIVE!

Inactivated Vaccines:
Inactivated vaccines, as the name implies, can produce a protective immune response without the risk of infection by the agent. They are used for agents that cannot be attenuated, that may cause recurrent infection, or that have ONOGENIC POTENTIAL.

Explanation

Vaccines containing killed pathogens or antigenic components (subunits like peptides) do not enter host cells. Hence, they induce a B cell-mediated humoral response. On the other hand, live ATTENUATED LIVE VACCINES do penetrate cells, eliciting a cell-mediated immune response against intracellular antigens. SO FOR INTRACELLULAR ORGANISMS, LIVE ATTENUATED VACCINES ARE MORE EFFECTIVE!

Inactivated Vaccines:
Inactivated vaccines, as the name implies, can produce a protective immune response without the risk of infection by the agent. They are used for agents that cannot be attenuated, that may cause recurrent infection, or that have ONOGENIC POTENTIAL.

15. A defect in expression of which molecule(s) on the surface of a B cell would prohibit B cell activation? A) CD19 B) IL‐2 receptor C) Igβ D) CD40L E) CD80/86

A only

A and C

A, B and D

C and D

A, C and E

A defect in the expression of CD19 and Igβ molecules on the surface of a B cell would prohibit B cell activation. CD19 is a co-receptor that plays a crucial role in B cell signaling and activation, while Igβ is a component of the B cell receptor complex that is essential for antigen recognition and signaling. Therefore, a defect in the expression of these molecules would impair the ability of B cells to respond to antigens and initiate an immune response.

Explanation

A defect in the expression of CD19 and Igβ molecules on the surface of a B cell would prohibit B cell activation. CD19 is a co-receptor that plays a crucial role in B cell signaling and activation, while Igβ is a component of the B cell receptor complex that is essential for antigen recognition and signaling. Therefore, a defect in the expression of these molecules would impair the ability of B cells to respond to antigens and initiate an immune response.