USMLE USMLE-STEP-1 Online Practice Questions and Exam Preparation

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 411:

  Which of the following ratios represents the estimated likelihood that a physician will become addicted to narcotics during his/her career?

  A. 1 in 10
  B. 1 in 100
  C. 1 in 1000
  D. 1 in 10,000
  E. 1 in 100,000
  B. 1 in 100

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  Explanation

  Section: Behavioral Science and Biostatics Because of easy drug availability and their high-stress occupation, physicians are at high risk for narcotic drug addiction; the incidence is estimated to be 1 in 100, which is 30 to 100 times greater than that of the general population. Choices A, C, D, and E are incorrect.

• Question 412:

  An injured firefighter developed a wound infection, and culture of the site indicates a gram-negative rod that is oxidase-positive and produces a bluish-green pigment. The organism was relatively resistant to antibiotics, but susceptible to ticarcillin and tobramycin. The organism is most likely to be identified as which of the following?

  B. Klebsiella pneumonia
  C. P. mirabilis
  D. P. aeruginosa
  E. Serratia marcescens
  D. P. aeruginosa

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  Explanation

  Section: Microbiology/Immunology

  P. aeruginosa is a gram-negative, oxidasepositive, aerobic rod that produces a greenblue pigment called pyocyanin. This microorganism has been associated frequently with wound infections in burn patients, and it is the second leading cause of burn infections after

  S. aureus.

  P. aeruginosa tends to develop resistance to various antibiotics. However, it may respond to ticarcillin, gentamycin, tobramycin, piperacillin, or azlocillin.

  E. coli (choice A),

  K. pneumoniae (choice B),

  P. mirabilis (choice C), and S.

  marcescens (choice E) may cause urinary or pulmonary tract infections, but are not considered leading causes of burn infections. Furthermore, these bacteria are oxidase negative and do not produce blue green pigments.

• Question 413:

  Which of the following is a normal sexual function?

  A. anorgasmia
  B. dyspareunia
  C. masturbation
  D. pedophilia
  C. masturbation

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  Explanation

  Section: Behavioral Science and Biostatics Masturbation is virtually universal among men and women of all cultures. It is common among married as well as single people. Many sex therapists recommend self-stimulation as an auxiliary treatment technique for a variety of sexual dysfunctions. Choices A, B, and D are sexual dysfunctions.

• Question 414:

  A female patient presents with swollen inguinal lymph nodes and painful lesions on the genitalia and perianal region. Which of the organisms below is the most likely causative agent for this infection?

  A. Group B streptococci
  B. Haemophilus aegypticus
  D. Moraxella (Branhamella) catarrhalis
  E. N. gonorrhoeae
  H. ducreyi
  C

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  Explanation

  Section: Microbiology/Immunology

  H. ducreyi (choice C) causes chancroid (soft chancre), a sexually transmitted disease. Chancroid consists of a ragged ulcer on the genetalia, with marked swelling and tenderness. The regional lymph nodes are usually enlarged and painful. Differential diagnosis must consider syphilis, HSV infection, or lymphogranuloma venereum. The organisms can usually be obtained from the lesions and often are part of a mixed infection. Scrapings from the lesion base are inoculated on to chocolate agar with X factor

  and vancomycin. No permanent immunity develops from chancroid infection, but the organism is treatable with ceftriaxone, TMS, or erythromycin. Group B streptococci (choice A) are usually a component of normal vaginal flora, but do not tend to be pathogenic to the host. Group B streptococci are most significant in new-born infections.

  H. egypticus (choice B) is most often found to be associated with conjunctivitis and Brazilian purpuric fever in children.

  M. catarrhailis (choice D) is a usual oral cavity

  organism and is considered to be an opportunist, although it has not been associated with genital infections. N. gonorrhoeae (choice E) will usually present as a mucus membrane infection with a discharge and not present as genital lesions.

• Question 415:

  Agrandmother undergoing chemotherapy for cancer in a hospital was exposed to a grandchild with chickenpox. In order to prevent a clinical complication of varicella or disseminated zoster in the grandmother, which of the materials listed below should be used as an appropriate medical intervention?

  A. acyclovir
  B. indinavir
  C. killed varicella-zoster virus (VZV) vaccine
  D. live attenuated VZV vaccine
  E. subunit VZV vaccine
  A. acyclovir

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  Explanation

  Section: Microbiology/Immunology Prevention of varicella and disseminated zoster rests on the administration of acyclovir. Killed varicella- zoster virus (VZV) vaccine has not been shown to be effective. Furthermore, if the immunological system has been compromised the immune responses will be very weak and of questionable value (choice C). Live attenuated VZV vaccines cannot be given to immunocompromised individuals because vaccination can be lethal (choice D). Subunit VZV vaccines are not available, and will be of little value to persons with suppressed immunological responses (choice E). Indinavir is a protease inhibitor used for the treatment of AIDS, not for varicella or zoster (choice B).

• Question 416:

  A 3-year-old child with a history of recurrent staphylococcal infections arrives at the emergency department at the local hospital. His neutrophils show normal chemotaxis, degranulation, and phagocytosis. However, intracellular killing of staphylococci by the neutrophils is severely impaired. Myeloperoxidase activity of his neutrophils is normal. The child has no history of streptococcal infection. Which of the following is the most likely disease affecting this patient?

  A. chronic granulomatous disease
  B. Graves disease
  C. rheumatoid arthritis
  D. severe combined immunodeficiency disease (SCID)
  E. systemic lupus erythematosus (SLE)
  A. chronic granulomatous disease

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  Explanation

  Section: Microbiology/Immunology This patient has chronic granulomatous disease. Children with this disease suffer chronic suppurative infections caused most frequently by S. aureus. The cause of chronic granulomatous disease is most commonly an X-linked disorder related to a genetic defect in NADPH oxidase, leading to a deficiency of NADPH oxidase. Neutrophils contain myeloperoxidase, which utilizes hydrogen peroxideand halide ions to produce hypochlorite, which is highly microbicidal. Because of the defective NADPH oxidase, the patient's phagocytes cannot generate sufficient hydrogen peroxide, thus the myeloperoxidase- hydrogen peroxide- halide system cannot function normally. Neutrophils from these patients can phagocytize bacteria and fungi normally, but they cannot kill them because of the defective myeloperoxidase-hydrogen peroxide-halide system. Also, laboratory analysis reveals an absent respiratory burst as demonstrated by a negative nitroblue tetrazolium test in patients with chronic granulomatous disease Severe combined immunodeficiency disease (SCID) is characterized by the absence of T and B cells, absence of thymus, and a lack of lymphocyte proliferative response to mitogens, antigens, and allogeneic cells in vitro (choice D). Systemic lupus erythematosus is an autoimmune disease (type III hypersensitivity or immune-complex disease). Patients with lupus erythematosus produce anti-DNA antibodies (choice E). Rheumatoid arthritis is another autoimmune disease. Patients with this disease produce IgM autoantibodies to the Fc moiety of IgG (choice C). Patients with Graves disease produce autoantibodies to thyroid-stimulating hormone receptors (choice B).

• Question 417:

  Following the consumption of fish at a local restaurant, a 17-year-old girl suddenly experiences severe dyspnea. Upon arrival at the local emergency room she is found to be severely hypotensive and in respiratory distress. Urticarial wheals are also noted all over her body. As the resident physician you quickly realize this to be a hypersensitivity reaction. To which of the following immunoglobulins does the allergen bind rapidly during the activation stage of mast cells?

  A. IgA
  B. IgD
  C. IgE
  D. IgG
  E. IgM
  C. IgE

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  Explanation

  Section: Microbiology/Immunology Within seconds after the allergen encounters human tissue, it binds to IgE antibodies which are attached to mast cells. When it engages at least two IgE molecules it forms a bridge between them. This cross-linking, in turn, draws the attached IgE receptors close to one another. Such aggregation of receptors activates mast cells to release histamine and other vasoactive substances that generate the allergic reaction. IgA, IgG, IgM, or IgD are not the germane antibodies to which allergens bind (choices A, B, D, and E).

• Question 418:

  A young child developed staphylococcal scalded syndrome. Which one of the following toxins is most likely responsible for this syndrome?

  A. alpha toxin
  B. erythrogenic toxin
  C. exfoliative toxin
  D. staphylococcal enterotoxins A through F
  E. toxic shock syndrome toxin (TSST)
  C. exfoliative toxin

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  Explanation

  Section: Microbiology/Immunology Exfoliation toxin is produced by certain strains of S. aureus belonging to phage group II. This exotoxin divides the epidermis between the stratum granulosum and the stratum spinosum. The end result of exfoliation action is the exfoliation of the skin, known as the staphylococcal scalded skin syndrome. The TSST (choice E) causes multisystem involvement with shock which can be lethal. TSST is a super antigen that releases large concentrations of IL-1, IL-2, and TNF. Erythrogenic toxin (choice B) is produced by S. pyogenes and is associated with scarlet fever. Alpha toxin (choice A) is produced by S. aureus and causes necrosis and hemolysis of blood cells. Staphylococcal enterotoxins A through F (choice D) are responsible for food poisoning.

• Question 419:

  In which of the following conditions would the gas composition of both end pulmonary capillary blood and alveolar air approximate that of mixed venous blood?

  A. airway obstruction
  B. breathing 100% oxygen
  C. hyperventilation
  D. normal breathing
  E. pulmonary capillary embolus
  A. airway obstruction

• Question 420:

  According to Erikson, which of the following is a major developmental task for most children around 15 years of age?

  A. developing a clear identity
  B. developing a sense of integrity
  C. developing intimate relationships
  D. learning about sex
  E. learning to be independent
  A. developing a clear identity

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  Explanation

  Section: Behavioral Science and Biostatics Erikson describes adolescence as the period of identity formation. In this period, a person develops a sense of inner sameness and continuity, a sense of direction and self. Career choices are also made during this phase. Failure of identity formation in this period results in "role confusion." Choices B and C refer to other developmental periods or non-Eriksonian task (choice D & E).