Match each patient's clinical presentation with the primary molecular mechanism of immune evasion or pathogenesis utilized by the causative organism.
- A 32-year-old pregnant woman presents with fever and myalgias after consuming unpasteurized cheese; blood cultures grow Gram-positive, non-spore-forming bacilli exhibiting tumbling motility at room temperature.Secretion of a cholesterol-dependent cytolysin that oligomerizes to form pores in the phagosomal membrane, facilitating cytosolic escape.
- A 24-year-old man treated successfully for purulent urethritis three months ago returns with an identical presentation; urethral swab demonstrates intracellular Gram-negative diplococci.Programmed homologous recombination between expression and silent genetic loci, resulting in continuous alteration of surface adherence appendages.
- A 45-year-old man receiving hemodialysis via a tunneled catheter develops acute endocarditis; blood cultures rapidly grow coagulase-positive, Gram-positive cocci in clusters.Expression of a specialized surface polypeptide that binds the Fc region of IgG, preventing complement fixation and subsequent opsonophagocytosis.
- A 62-year-old man with a history of prolonged incarceration presents with chronic cough, night sweats, and apical cavitary lung disease; sputum smear reveals acid-fast bacilli.Production of complex cell-wall glycolipids that inhibit calcium-dependent recruitment of early endosomal autoantigen 1, arresting phagolysosome maturation.
Answer
The correct pairings are: the pregnant woman with Listeria matches phagosomal escape via cytolysin; the man with recurrent gonorrhea matches continuous alteration of surface appendages via recombination; the hemodialysis patient with Staphylococcus aureus matches binding of the IgG Fc region; and the incarcerated man with tuberculosis matches the inhibition of phagolysosome maturation.
Each pairing correctly maps a clinical scenario to the foundational virulence mechanism of the responsible pathogen. The pregnant patient with a Gram-positive motile rod is infected with Listeria monocytogenes, which uses listeriolysin O to form pores and escape the phagosome. The young man with recurrent gonorrhea lacks protective immunity because Neisseria gonorrhoeae constantly varies its pilin proteins via homologous recombination. The hemodialysis patient with coagulase-positive Staphylococcus aureus bacteremia suffers from an infection facilitated by Protein A, which binds the Fc portion of IgG to block complement activation and opsonization. Finally, the man with cavitary tuberculosis is infected by Mycobacterium tuberculosis, an organism that uses sulfatides and cord factor to inhibit EEA1, preventing phagolysosome fusion and allowing intracellular survival.
Step-by-Step Solution
Key Concept
Successful human pathogens utilize highly specific molecular mechanisms to evade the immune system, such as escaping the phagosome (Listeria), varying surface antigens to prevent protective immunity (Neisseria), neutralizing opsonizing antibodies (Staphylococcus), and arresting intracellular clearance pathways (Mycobacterium).
Estimated Time:1m 30s