A sputum smear from a patient with pneumonia revealed Gram-positive cocci in pairs with pointed ends and capsules. What is the likely microorganism?

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. The description of Gram-positive cocci in pairs with pointed ends and capsules matches the morphology of S. pneumoniae. This bacterium is known to cause pneumonia, especially in individuals with underlying conditions like COPD. Staphylococcus aureus (B) typically appears in clusters, not pairs. Klebsiella pneumoniae (C) is a Gram-negative rod, not a cocci. Neisseria meningitidis (D) is a Gram-negative diplococcus, not a cocci. Hence, based on the morphology and clinical context, Streptococcus pneumoniae is the likely microorganism causing pneumonia in this patient.

Correct Answer: C

Rationale: Correct Answer: C: Halophiles Rationale: 1. Halophiles are bacteria adapted to high salt environments. 2. They have specific mechanisms to tolerate high salt concentrations. 3. Acidophiles thrive in acidic conditions. 4. Thermophiles prefer high temperature environments. 5. Mesophiles grow best at moderate temperatures.

Correct Answer: A

Rationale: The most likely diagnosis is Epidemic typhus (Choice A) based on the symptoms described. The presence of roseolous-petechial rash, high fever (41oC), hyperemia of face, reddening of scleras, tremor of the tongue, tachycardia, and splenomegaly are classic signs of epidemic typhus. The rash typically appears around the 5th day of the disease. Summary: - B: Measles typically presents with a maculopapular rash starting on the face and spreading downward. It doesn't usually present with tremor of the tongue or splenomegaly. - C: Alcohol delirium is characterized by confusion, disorientation, and hallucinations due to alcohol consumption. It doesn't match the symptoms described. - D: Leptospirosis presents with fever, muscle pain, and conjunctival suffusion. It doesn't typically present with the specific rash and trem

Correct Answer: B

Rationale: The correct answer is B: Yersinia pestis. Yersinia pestis is the bacterium responsible for causing the plague, specifically the bubonic plague. It is transmitted through fleas and rodents. Escherichia coli (A) is a common gut bacterium, Clostridium difficile (C) causes antibiotic-associated diarrhea, and Staphylococcus aureus (D) is associated with skin infections, but they are not responsible for causing the plague.

Correct Answer: D

Rationale: Step-by-step rationale for why answer choice D is correct: 1. Coronaviruses can cause reinfections due to potential waning immunity. 2. Studies have shown cases of reinfections with different strains or within a short period. 3. This contradicts the notion that reinfections cannot be observed. Summary: A: Incorrect because some coronaviruses can cause lower respiratory tract infections. B: Incorrect as coronaviruses can exhibit varied symptomatology including asymptomatic cases. C: Incorrect as some coronaviruses like SARS can lead to severe pneumonia and complications.

Correct Answer: A

Rationale: The correct answer is A: Neisseria meningitidis. This is because Neisseria meningitidis is a Gram-negative diplococcus known to cause bacterial meningitis, presenting with fever, headache, and neck stiffness. It is a common cause of meningitis in young adults and teenagers. Streptococcus pneumoniae (B) is a Gram-positive bacteria and a common cause of bacterial pneumonia, not meningitis. Haemophilus influenzae (C) is a Gram-negative coccobacillus that can cause meningitis, but it is less common in adults. Klebsiella pneumoniae (D) is a Gram-negative bacillus known to cause pneumonia and urinary tract infections, not meningitis.

Correct Answer: B

Rationale: The capsule of Bacillus anthracis is made of polypeptide. This is because the capsule is composed of a protein-based material that surrounds the bacterium, providing protection and aiding in its virulence. Polysaccharides, lipids, and the absence of capsules are not characteristic of Bacillus anthracis' capsule structure, making choices A, C, and D incorrect, respectively.

Correct Answer: B

Rationale: The correct answer is B: Alpha-hemolytic streptococci. Streptococcus pneumoniae are classified as alpha-hemolytic streptococci based on their ability to partially break down red blood cells, causing a greenish discoloration on blood agar plates. This distinguishes them from beta-hemolytic streptococci, which completely break down red blood cells. Streptococcus pneumoniae are not resistant to bile (choice A), as they are bile soluble. They are not stained by the Ziehl-Neelsen staining method (choice C), which is used for acid-fast bacteria such as Mycobacterium tuberculosis. They are sensitive to optochin (choice D), which is a key differentiating factor in identifying them from other alpha-hemolytic streptococci.

Correct Answer: B

Rationale: The correct answer is B: Syphilis. The Wasserman reaction is a test for syphilis, specifically for detecting antibodies against the bacterium Treponema pallidum. In a 30-year-old man with a markedly positive Wasserman reaction, it indicates an active syphilis infection. Brucellosis (Choice A) is not diagnosed using the Wasserman reaction. Poliomyelitis (Choice C) is a viral infection affecting the spinal cord, not diagnosed using the Wasserman reaction. Influenza (Choice D) is a respiratory viral infection, not associated with the Wasserman reaction.