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A patient with fever and sore throat had a throat culture revealing Gram-positive cocci in chains. The bacteria were catalase-negative and beta-hemolytic. What is the most likely causative agent?
- A. Streptococcus pyogenes
- B. Streptococcus pneumoniae
- C. Enterococcus faecalis
- D. Staphylococcus aureus
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pyogenes.
1. Gram-positive cocci in chains: characteristic of Streptococcus species.
2. Catalase-negative: Streptococcus species are catalase-negative.
3. Beta-hemolytic: S. pyogenes is beta-hemolytic on blood agar.
Therefore, S. pyogenes fits all these criteria.
B: Streptococcus pneumoniae is catalase-negative but alpha-hemolytic, not beta-hemolytic.
C: Enterococcus faecalis is catalase-negative, but not typically beta-hemolytic or in chains.
D: Staphylococcus aureus is catalase-positive and not in chains.
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Etiological cause of bacteremia could be:
- A. S.epidermidis, E.coli, S. aureus
- B. P.aeruginosa, K. pneumoniae, E.coli
- C. Resident skin diphtheroids
- D. All of the above
Correct Answer: D
Rationale: The correct answer is D because bacteremia can be caused by a variety of bacteria including S.epidermidis, E.coli, S.aureus, P.aeruginosa, K.pneumoniae, and resident skin diphtheroids. Bacteremia refers to the presence of bacteria in the bloodstream, which can occur due to infections from various sources. Choices A and B include common bacteria known to cause bacteremia, while choice C refers to resident skin diphtheroids that can also enter the bloodstream under certain conditions. Therefore, the correct answer is D as it encompasses all the possible etiological causes of bacteremia.
Microscopy of sputum from a tuberculosis patient revealed acid-fast rods stained red using the Ziehl-Neelsen method. What structural feature allows this staining?
- A. Mycolic acid in the cell wall
- B. Capsule surrounding the cell
- C. Flagella on the cell surface
- D. Thick peptidoglycan layer
Correct Answer: A
Rationale: The correct answer is A: Mycolic acid in the cell wall. Mycolic acid is a unique component of the cell wall of Mycobacterium species, including the causative agent of tuberculosis. The Ziehl-Neelsen method uses acid-fast staining, where mycolic acid confers resistance to decolorization by acid-alcohol, causing the bacteria to retain the red stain. Choices B, C, and D are incorrect as capsules, flagella, and peptidoglycan layers do not directly contribute to acid-fast staining characteristic of Mycobacterium species.
Salmonellosis is caused by:
- A. Salmonella typhi
- B. Salmonella enteritidis
- C. Shigella flexneri
- D. None of the above
Correct Answer: B
Rationale: The correct answer is B: Salmonella enteritidis. Salmonellosis is typically caused by Salmonella species, with Salmonella enteritidis being one of the common culprits. Salmonella typhi causes typhoid fever, not salmonellosis. Shigella flexneri is responsible for causing shigellosis, a different bacterial infection. Choosing "None of the above" is incorrect as Salmonella enteritidis is a known cause of salmonellosis.
Which of the following bacteria is known for causing the disease tetanus?
- A. Clostridium tetani
- B. Clostridium perfringens
- C. Streptococcus pyogenes
- D. Escherichia coli
Correct Answer: A
Rationale: The correct answer is A: Clostridium tetani. This bacterium is known for causing tetanus due to its ability to produce tetanospasmin, a neurotoxin that leads to the characteristic muscle stiffness and spasms seen in tetanus. Clostridium perfringens (Choice B) is associated with gas gangrene, Streptococcus pyogenes (Choice C) causes streptococcal infections, and Escherichia coli (Choice D) is known for causing various gastrointestinal infections. Therefore, Choices B, C, and D are incorrect as they are not the causative agents of tetanus.
Immunity after single vaccination against tetanus - application of tetanus toxoid is:
- A. intense and usually life long
- B. of limited duration, booster vaccinations are needed
- C. infectious (non-sterile)
- D. no correct answer
Correct Answer: B
Rationale: The correct answer is B. Immunity after a single tetanus vaccination is of limited duration, usually around 10 years. Booster vaccinations are needed to maintain protection due to waning immunity over time. Choice A is incorrect as immunity is not usually lifelong. Choice C is incorrect as tetanus toxoid is a sterile vaccine and does not cause infection. Choice D is also incorrect as there is a correct answer, which is B.