Nokea
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.
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A patient with a sore throat and fever had a throat culture revealing Gram-positive cocci in chains. The bacteria were 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 suggest streptococci.
2. Beta-hemolytic activity indicates Streptococcus pyogenes.
3. Streptococcus pyogenes is commonly associated with sore throat (pharyngitis) and fever.
4. Streptococcus pneumoniae (choice B) is alpha-hemolytic and mainly causes pneumonia.
5. Enterococcus faecalis (choice C) is not typically associated with sore throat.
6. Staphylococcus aureus (choice D) is not commonly beta-hemolytic and is not a typical cause of pharyngitis.
Which are the epidemic typhus vectors:
- A. Head lice
- B. Body lice
- C. Fleas
- D. Ticks
Correct Answer: A
Rationale: The correct answer is A: Head lice. Epidemic typhus is transmitted by the body louse, Pediculus humanus humanus, which is different from the head louse, Pediculus humanus capitis. Head lice are not known to transmit epidemic typhus. Body lice are the primary vectors for transmitting epidemic typhus. Fleas are vectors for other diseases such as plague, not epidemic typhus. Ticks are vectors for various diseases but not for epidemic typhus. Therefore, the correct vector for epidemic typhus transmission is body lice, making choice A the correct answer.
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.
A wound culture grew Gram-negative rods that were oxidase-positive and lactose non-fermenters. What is the most likely microorganism?
- A. Pseudomonas aeruginosa
- B. Escherichia coli
- C. Salmonella typhi
- D. Shigella dysenteriae
Correct Answer: A
Rationale: The correct answer is A: Pseudomonas aeruginosa. P. aeruginosa is a Gram-negative rod that is oxidase-positive and lactose non-fermenting. The positive oxidase test indicates the presence of cytochrome c oxidase, a characteristic of P. aerugin. E. coli is lactose fermenting. Salmonella and Shigella are also Gram-negative rods, but they are lactose fermenters, unlike the lactose non-fermenting P. aeruginosa.
Name the halogen-containing antiseptic with fungicidal properties, which is used to treat dermatomycosis:
- A. Iodine solution
- B. Formalin solution
- C. Methylene blue
- D. Brilliant green
Correct Answer: A
Rationale: Rationale:
1. Iodine solution contains iodine, a halogen with antiseptic properties.
2. Iodine is effective against fungi, making it suitable for treating dermatomycosis.
3. Iodine solution is commonly used in dermatology for its fungicidal properties.
4. Formalin, methylene blue, and brilliant green do not contain halogens or have fungicidal properties.
Summary:
- Formalin is a disinfectant, not an antiseptic for dermatomycosis.
- Methylene blue is an antifungal dye, not used as an antiseptic.
- Brilliant green is an antiseptic, but does not contain halogens or have fungicidal properties.