A 5-year-old boy is brought to the emergency department by his parents for severe respiratory distress. He has not received any immunizations due to parental preference, and his medical history is otherwise unremarkable. The patient appears very uncomfortable and anxious. He is leaning forward and making a loud, harsh sound with every inspiration. Temperature is 39.6 C (103.4 F). The patient is intubated immediately. During intubation, the epiglottis is visualized and appears markedly swollen and erythematous. Which of the following is a major virulence factor of the pathogen causing this patient's infection?

Question

A 5-year-old boy is brought to the emergency department by his parents for severe respiratory distress.  He has not received any immunizations due to parental preference, and his medical history is otherwise unremarkable.  The patient appears very uncomfortable and anxious.  He is leaning forward and making a loud, harsh sound with every inspiration.  Temperature is 39.6 C (103.4 F).  The patient is intubated immediately.  During intubation, the epiglottis is visualized and appears markedly swollen and erythematous.  Which of the following is a major virulence factor of the pathogen causing this patient's infection?

Quizplus · Accepted Answer

11ec160b_389c_961a_9249_5b168a66e96d_MD0001_00 This child's fever, respiratory distress, and inflamed epiglottis are consistent with epiglottitis, which is most commonly caused by Haemophilus influenzae type b (Hib). The infected epiglottis swells, causing inspiratory stridor, dyspnea, and severe agitation. Epiglottitis is confirmed by direct visualization or radiographic evidence of a swollen epiglottis (ie, "thumbprint sign"). The major virulence factor of Hib is its polysaccharide capsule, which is composed of the polymer polyribosylribitol phosphate (PRP). The PRP capsule protects the bacterium against phagocytosis and complement-mediated lysis by binding factor H, a circulating regulator protein that normally prevents complement (C3b) deposition on host cells. The conjugate Hib vaccine is composed of PRP conjugated to a protein toxoid. Immunization results in host development of anti-PRP antibody, which leads to improved opsonization and complement-mediated phagocytosis. Invasive Hib disease is rare in immunized patients, but it still occurs regularly in unimmunized children. (Choice A) Lecithinase (toxin A) is produced by Clostridium perfringens, and hydrolyzes lecithin in cell membranes. This results in cell lysis and the development of gas gangrene. (Choice B) M protein is found in the cell wall of Streptococcus pyogenes. It binds factor H to prevent opsonization and destruction of streptococci by the alternative complement pathway. (Choice D) Protein A in the cell wall of Staphylococcus aureus helps prevent opsonization by binding the Fc region of immunoglobulins. S aureus is a common cause of tracheitis, which presents similarly to epiglottitis (eg, stridor, fever, respiratory distress) but does not cause a swollen epiglottis. (Choice E) Trehalose dimycolate is a cell wall component and major virulence factor of Mycobacterium tuberculosis. It protects M tuberculosis from being killed by macrophages and stimulates granuloma formation. Educational objective: Polyribosylribitol phosphate is a capsule component and major virulence factor for Haemophilus influenzae type b (Hib). Hib is the most common cause of epiglottitis, which presents with fever, stridor, and dyspnea. __________ References: Hib vaccines: past, present, and future perspectives. (http://www.ncbi.nlm.nih.gov/pubmed/26904695)

A 5-Year-Old Boy Is Brought to the Emergency Department by His