Question 1

A burn patient has an infected area with odiferous, blue-green pus. What is the most likely causative agent?

Accepted Answer

Most strains of Pseudomonas aeruginosa produce a blue-green pigment, which is clinically notable in burn wounds infected with Pseudomonas. (Colonization is common but the presence of the blue-green pus is suggestive of actual presence in the tissue and infection.)

Question 2

A 14-year-old girl has symptoms that include a low-grade fever, chills, headache, muscle aches, and malaise. A physical examination indicates an enlarged spleen. A Monospot test is negative. The laboratory finding that would confirm a diagnosis would be

Accepted Answer

Symptoms are consistent with a mononucleosis disease that is usually caused by EBV or CMV. The lack of a positive Monospot test for heterophile antibodies and presence of "owl's eye" cells would indicate CMV.

Question 3

A 20-year-old female has signs and symptoms consistent with genital warts. What would have been the best approach to prevent this disease?

Accepted Answer

A quadrivalent recombinant vaccine (Gardasil) containing viruslike particles of types 6, 11, 16, and 18 (these types cause 90% of genital warts) is available for prophylactic immunization to prevent genital warts and cervical cancer by types 16 and 18.

Question 4

One advantage of live, attenuated vaccines is

Accepted Answer

A live attenuated vaccine has the advantage of producing persistent infection, thus continuously stimulating the immune system with different antigens. A few viral strains in vaccines may revert to virulent form. A disadvantage is their limited shelf life.

Question 5

Which of the following childhood vaccines is most likely to prevent otitis media in young children?

Accepted Answer

Of the organisms listed, H. influenzae is the one most likely to cause otitis media.

Question 6

A patient with a chronic cough is given a tuberculin skin test, which when properly read has a zone of induration greater than 15 mm. What does this mean?

Accepted Answer

The tuberculin test indicates previous infection with Mycobacterium tuberculosis or Mycobacterium bovis from between several weeks to 5 years. It does not provide proof of current active infection with M. tuberculosis. The tuberculin test detects cell-mediated immunity and not antibody. If a person is infected with a nontuberculous strain of mycobacteria, usually the skin reaction is smaller. Specific skin tests for some of these nontuberculous strains of mycobacteria are available. Vaccination with bacillus Calmette-Guérin (BCG) vaccine should not result in this large a zone of induration. The newer whole blood interferon-gamma release assays (IGRAs), which also do not distinguish latent tuberculosis infection from tuberculosis disease, are superior to distinguish infected from BCG vaccinated.

Question 7

The role of macrophages in the immune response includes all of the following functions except

Accepted Answer

Macrophages do not produce IL-2.

Question 8

A patient with a cough of several weeks' duration but no fever has radiological signs of a coin lesion. The needle biopsy shows large, broad-based budding yeasts with a very thick cell wall. Most of the yeasts are extracellular. What is the most likely diagnosis?

Accepted Answer

The picture given is classical for the pulmonary lesions of blastomycosis, which cannot be differentiated from carcinoma without biopsy.

Question 9

A 12-day-old neonate is brought in because of parental concern about eye redness and "watering" associated with the conjunctiva of both eyes. Visual examination confirms and also detects several vesicles. Appropriate topical treatment is with

Accepted Answer

This is conjunctivitis caused by HSV-1 or -2, which should be treated by an ophthalmologist with the antiherpes drug acyclovir. But the child should also be receiving IV acyclovir for potential systemic infection.

Question 10

$beta-lactam$ drugs bind to penicillin-binding proteins to halt the synthesis of peptidoglycan. Where are these proteins located?

Accepted Answer

The PBPs are actually in the cytoplasmic membrane, even though the substrate is the cell peptidoglycan. Thus, $\beta$-lactams must penetrate the Gram-negative outer membrane through the porins and cross the peptidoglycan to bind. In the Gram-positive bacteria, they just have to cross the peptidoglycan to bind in the membrane.

Question 11

A new class of pathogen appears, causing pneumonia. It appears to be some sort of budding yeastlike organism with chitin in the cell wall, but the nucleus is not membrane bound and the protein synthetic equipment appears to be procaryotic. Which of the following antimicrobial agents is most likely to be effective?

Accepted Answer

Metronidazole (choice A) is not likely to work, as the agent is causing pneumonia, so it is probably aerobic or a facultative anaerobe. If the cell wall does not include peptidoglycan, $\beta$-lactam drugs (choices B and C) are likely to be ineffective. However, since the ribosomes are procaryotic, doxycycline has the best chance as long as it can penetrate the pathogen's cell wall and cytoplasmic membrane.

Question 12

A typical IgG antibody molecule has all of the following characteristics except

Accepted Answer

The IgG molecule has three constant domains on the heavy chain.

Question 13

A 59-year-old man presents at the emergency department with labored breathing and a sharp stabbing pain behind the breast bone. He complains of being weak and tired. He has a low-grade fever and an electrocardiogram shows elevated ST segments. The most likely infectious cause of these symptoms is

Accepted Answer

Viruses are the major infectious agents that produce symptoms similar to a heart attack. The most common of these viruses is Coxsackie B virus.

Question 14

A 27-year-old worker at a day care center has recently been feeling tired, has a slight fever, and has felt nauseated and vomited several times. Yesterday, she had abdominal pain and chills, and today she voided dark urine. Lab tests for serum enzymes indicated elevated AST and ALT. The genetic material of the virus most likely to cause her symptoms is

Accepted Answer

Hepatitis A virus (HAV) is the most likely virus to cause the reported symptoms, which indicate hepatitis rather than some other disease. HAV is a positive-sense single-strand RNA virus.

Question 15

The T-cell antigen receptor is associated with which of the following characteristics?

Accepted Answer

The T-cell antigen receptor is specific, responding only to antigen fragments bound to HLA. Choice A describes the B-cell receptor.

Question 16

Which of the following cells is capable of attacking a certain tumor cell spontaneously (i.e., without prior sensitization)?

Accepted Answer

Natural killer cells target cells not expressing MHC Class I antigen for cytolysis. Many transformed cells and neoplasitic cells are loose the expression of MHC class I on their cell surface.

Question 17

A 40-year-old man presents to the ED with a painful and swollen jaw. Two days ago he had a tooth extraction where the gums and jaw were swollen and painful. "Nodules" are felt below the surface of the tissues which are not lymph nodes. Which member of the gingival normal flora will grow contiguously into the damaged tissues, producing tissue swelling and ultimately, if untreated, will develop sinus tracts that will erupt to the surface, liberating the "nodules"?

Accepted Answer

Actinomyces israelii grows contiguously in tissues, crossing anatomic barriers and causing a lumpy jaw, which is characterized by swelling and, sometimes, sinus tract formation with sulfur granules (3D colonies). It also invades bone. M. tuberculosis may be hematogenously spread to any tissue but is not associated with tooth extraction. Nocardia can also cause a similar infection, but the source is usually environmental nocardiae introduced by trauma; therefore, it generally involves extremities.

Question 18

Bacteria are protected from phagocytosis by

Accepted Answer

In the immunologically naive, bacterial capsules prevent the phagocytic uptake and, therefore, the killing of the bacterium.

Question 19

Which of the following genetic mechanisms is responsible for the conversion of nontoxigenic strains of Corynebacterium diphtheriae to toxigenic strains?

Accepted Answer

A toxigenic strain of Corynebacterium diphtheriae is produced as a result of lysogenic phage conversion after a temperate bacteriophage infects a nontoxigenic strain of the organism.

Question 20

Parents bring in a 5-month-old who suddenly has lost developmental ground and is no longer able to hold his head up or sit up. In taking the health history, they did note constipation a couple of days before. The EEG confirms a pattern consistent with botulism. After assuring them that with monitoring and support the child will survive, the parents become terribly concerned that the loss of development might be permanent. What can you tell them about their child's prognosis?

Accepted Answer

The neurotoxin involved in infant botulism, unlike bacterial meningitis, does not cause elevated cerebrospinal fluid pressure, so recovery should be complete. The use of the recombinant human antitoxin shortens hospitalization and recovery time. However, it still requires regrowth of nerve endings.

Quiz 11: Travelers Diarrhea: Identifying the Causative Agent

A burn patient has an infected area with odiferous, blue-green pus. What is the most likely causative agent?

A 14-year-old girl has symptoms that include a low-grade fever, chills, headache, muscle aches, and malaise. A physical examination indicates an enlarged spleen. A Monospot test is negative. The laboratory finding that would confirm a diagnosis would be

A 20-year-old female has signs and symptoms consistent with genital warts. What would have been the best approach to prevent this disease?

One advantage of live, attenuated vaccines is

Which of the following childhood vaccines is most likely to prevent otitis media in young children?

A patient with a chronic cough is given a tuberculin skin test, which when properly read has a zone of induration greater than 15 mm. What does this mean?

The role of macrophages in the immune response includes all of the following functions except

A patient with a cough of several weeks' duration but no fever has radiological signs of a coin lesion. The needle biopsy shows large, broad-based budding yeasts with a very thick cell wall. Most of the yeasts are extracellular. What is the most likely diagnosis?

A 12-day-old neonate is brought in because of parental concern about eye redness and "watering" associated with the conjunctiva of both eyes. Visual examination confirms and also detects several vesicles. Appropriate topical treatment is with

$beta-lactam$ drugs bind to penicillin-binding proteins to halt the synthesis of peptidoglycan. Where are these proteins located?

A typical IgG antibody molecule has all of the following characteristics except

A 59-year-old man presents at the emergency department with labored breathing and a sharp stabbing pain behind the breast bone. He complains of being weak and tired. He has a low-grade fever and an electrocardiogram shows elevated ST segments. The most likely infectious cause of these symptoms is

The T-cell antigen receptor is associated with which of the following characteristics?

Which of the following cells is capable of attacking a certain tumor cell spontaneously (i.e., without prior sensitization) ?

Bacteria are protected from phagocytosis by

Which of the following genetic mechanisms is responsible for the conversion of nontoxigenic strains of Corynebacterium diphtheriae to toxigenic strains?

Quiz 11: Travelers Diarrhea: Identifying the Causative Agent

A burn patient has an infected area with odiferous, blue-green pus. What is the most likely causative agent?

A 14-year-old girl has symptoms that include a low-grade fever, chills, headache, muscle aches, and malaise. A physical examination indicates an enlarged spleen. A Monospot test is negative. The laboratory finding that would confirm a diagnosis would be

A 20-year-old female has signs and symptoms consistent with genital warts. What would have been the best approach to prevent this disease?

One advantage of live, attenuated vaccines is

Which of the following childhood vaccines is most likely to prevent otitis media in young children?

A patient with a chronic cough is given a tuberculin skin test, which when properly read has a zone of induration greater than 15 mm. What does this mean?

The role of macrophages in the immune response includes all of the following functions except

A patient with a cough of several weeks' duration but no fever has radiological signs of a coin lesion. The needle biopsy shows large, broad-based budding yeasts with a very thick cell wall. Most of the yeasts are extracellular. What is the most likely diagnosis?

A 12-day-old neonate is brought in because of parental concern about eye redness and "watering" associated with the conjunctiva of both eyes. Visual examination confirms and also detects several vesicles. Appropriate topical treatment is with

beta−lactambeta-lactambeta−lactam drugs bind to penicillin-binding proteins to halt the synthesis of peptidoglycan. Where are these proteins located?

A typical IgG antibody molecule has all of the following characteristics except

A 59-year-old man presents at the emergency department with labored breathing and a sharp stabbing pain behind the breast bone. He complains of being weak and tired. He has a low-grade fever and an electrocardiogram shows elevated ST segments. The most likely infectious cause of these symptoms is

The T-cell antigen receptor is associated with which of the following characteristics?

Which of the following cells is capable of attacking a certain tumor cell spontaneously (i.e., without prior sensitization) ?

Bacteria are protected from phagocytosis by

Which of the following genetic mechanisms is responsible for the conversion of nontoxigenic strains of Corynebacterium diphtheriae to toxigenic strains?

$beta-lactam$ drugs bind to penicillin-binding proteins to halt the synthesis of peptidoglycan. Where are these proteins located?