Nokea
The classic causative agent of croupous pneumonia is:
- A. Chlamydia pneumoniae
- B. Streptococcus pneumoniae
- C. Mycoplasmas pneumoniae
- D. Staphylococcus aureus
Correct Answer: B
Rationale: The correct answer is B, Streptococcus pneumoniae. This bacterium is the classic causative agent of croupous pneumonia due to its ability to infect the lungs and cause inflammation. Streptococcus pneumoniae is a common pathogen known for causing pneumonia in both adults and children. It is characterized by the presence of a capsule that helps it evade the host immune system.
Choice A, Chlamydia pneumoniae, is not the correct answer as it is more commonly associated with atypical pneumonia. Choice C, Mycoplasma pneumoniae, is also associated with atypical pneumonia and not croupous pneumonia. Choice D, Staphylococcus aureus, can cause pneumonia, but it is not the classic causative agent of croupous pneumonia.
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Which of the following bacteria is responsible 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 responsible for causing tetanus due to its production of tetanus toxin. Clostridium perfringens (B) causes gas gangrene, Streptococcus pyogenes (C) causes strep throat and skin infections, and Escherichia coli (D) is a common gut bacteria that can cause food poisoning but not tetanus.
Which of the following is true about plasmids?
- A. They are linear DNA structures
- B. They are only found in gram-positive bacteria
- C. They often carry antibiotic resistance genes
- D. They are part of the bacterial chromosome
Correct Answer: C
Rationale: Plasmids often carry antibiotic resistance genes, making choice C correct. Plasmids are circular DNA structures, not linear (A). They are found in both gram-positive and gram-negative bacteria, not exclusively in gram-positive bacteria (B). Plasmids are separate from the bacterial chromosome, not part of it (D). Therefore, choice C is the correct answer.
Which of the following bacteria can be transmitted via droplets in the air?
- A. Streptococcus pneumoniae
- B. Escherichia coli
- C. Clostridium botulinum
- D. Mycobacterium tuberculosis
Correct Answer: D
Rationale: The correct answer is D: Mycobacterium tuberculosis. This bacterium can be transmitted via droplets in the air through coughing or sneezing. It is spread through respiratory droplets containing the bacteria. Streptococcus pneumoniae (A) is transmitted through direct contact with respiratory secretions, not through droplets in the air. Escherichia coli (B) is commonly transmitted through contaminated food or water, not through the air. Clostridium botulinum (C) is typically transmitted through contaminated food, not via respiratory droplets. Therefore, the correct choice is D as it is the only bacterium listed that can be transmitted via droplets in the air.
A bacteriophage is a(n) ____________ virus.
- A. helical
- B. icosahedral
- C. enveloped
- D. complex
Correct Answer: D
Rationale: The correct answer is D: complex. Bacteriophages are considered complex viruses because they have a complex structure consisting of a polyhedral head, a helical tail, and tail fibers. The head contains the viral genetic material, while the tail facilitates attachment to the host bacterial cell. This complexity distinguishes bacteriophages from simpler viruses like helical and icosahedral viruses. Helical viruses have a rod-like shape, while icosahedral viruses have a symmetrical, 20-sided structure. Enveloped viruses have a lipid bilayer envelope surrounding their capsid, which bacteriophages lack. Therefore, the unique and intricate structure of bacteriophages classifies them as complex viruses.
A child with fever and a sore throat had a Gram-stained smear revealing Gram-positive cocci in chains. The bacteria were beta-hemolytic. What is the likely causative agent?
- A. Streptococcus pyogenes
- B. Streptococcus pneumoniae
- C. Staphylococcus aureus
- D. Enterococcus faecalis
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pyogenes. The presence of Gram-positive cocci in chains suggests a streptococcal infection. Beta-hemolysis indicates the production of a hemolysin that lyses red blood cells, a characteristic of Streptococcus pyogenes. This bacterium is known to cause strep throat and can present with fever and sore throat.
Summary:
- B: Streptococcus pneumoniae is a common cause of pneumonia but typically appears as lancet-shaped cocci, not in chains.
- C: Staphylococcus aureus is a gram-positive cocci in clusters, not chains, and is not typically beta-hemolytic.
- D: Enterococcus faecalis is a gram-positive cocci that are part of the normal gut flora and are not typically beta-hemolytic or found in chains.