A 40-year-old woman comes to the emergency department due to malaise, fever, productive cough, and pleuritic chest pain. The patient has a history of alcohol use disorder and HIV acquired from injection drug use. She is nonadherent with antiretroviral therapy and other HIV-related medications. Temperature is 38.3 C (101 F), blood pressure is 120/72 mm Hg, and pulse is 104/min. Lung examination reveals bronchial breath sounds and crackles. Sputum microscopy findings are shown below. Which of the following pathogenic factors most likely contributes to this microorganism's ability to cause lung infection?

Question

A 40-year-old woman comes to the emergency department due to malaise, fever, productive cough, and pleuritic chest pain.  The patient has a history of alcohol use disorder and HIV acquired from injection drug use.  She is nonadherent with antiretroviral therapy and other HIV-related medications.  Temperature is 38.3 C (101 F), blood pressure is 120/72 mm Hg, and pulse is 104/min.  Lung examination reveals bronchial breath sounds and crackles.  Sputum microscopy findings are shown below.  Which of the following pathogenic factors most likely contributes to this microorganism's ability to cause lung infection?

Quizplus · Accepted Answer

Streptococcus pneumoniae is a gram-positive, lancet-shaped organism that grows in pairs (diplococci). It colonizes the nasopharynx and is a leading cause of community-acquired pneumonia, bacterial meningitis, sinusitis, otitis media, and sepsis. The major virulence factor of S pneumoniae is a thick polysaccharide capsule, which impedes phagocytosis and complement binding. Antibodies against the capsule form during infection and are protective against future infections with that strain. However, over 90 capsular serotypes have been identified. Therefore, previous infection is rarely protective against future infection. Other S pneumoniae virulence factors include IgA protease (inactivates secretory IgA), adhesins (necessary for adhesion to epithelial cells), and pneumolysin (a cytotoxin that causes pores in cell membranes and cell lysis). Patients with HIV are at higher risk than the general population for S pneumoniae infection because HIV impairs opsonizing antibody production, phagocyte recruitment, and cytokine signaling, which are crucial for the control of encapsulated pathogens. Most patients with HIV should receive the pneumococcal vaccine, which contains polysaccharide antigens from the most common strains. (Choice A) Alveolar hyaline membranes are fibrinous deposits that line the alveoli and inhibit gas transfer. They usually result in significant dyspnea and/or respiratory collapse, and are typically seen with newborn and acute respiratory distress syndromes. (Choice C) Endotoxins (eg, lipopolysaccharide) are found in the outer membrane of gram-negative pathogens (eg, Neisseria) and produce a strong inflammatory response when released into the circulation. Gram-positive organisms do not have endotoxins but some release exotoxins. (Choice D) Intracellular organisms such as Neisseria, Listeria, and Mycobacterium tuberculosis are protected from immunoglobulin and complement binding. S pneumoniae is an extracellular pathogen. (Choice E) Mycobacteria have lipid-rich mycolic acid in their cell walls, which causes them to be acid-fast. Mycolic acids inhibit bacterial destruction by the phagolysosome and contribute to granuloma formation. Educational objective: The virulence of Streptococcus pneumoniae is predominantly due to its polysaccharide capsule, which impedes phagocytosis and complement binding.

A 40-Year-Old Woman Comes to the Emergency Department Due to Malaise