Nokea
The most important virulence factor of Neisseria meningitidis is:
- A. Exotoxin
- B. Polysaccharide capsule
- C. Beta-lactamase
- D. Pyrogenic toxin
Correct Answer: B
Rationale: The correct answer is B: Polysaccharide capsule. The capsule of Neisseria meningitidis is crucial for its virulence as it helps the bacteria evade the host immune system by inhibiting phagocytosis. This allows the bacteria to survive and multiply in the host, leading to invasive infections. Exotoxins, beta-lactamase, and pyrogenic toxins are not the main virulence factors of Neisseria meningitidis and do not play as significant a role in its pathogenicity as the polysaccharide capsule.
You may also like to solve these questions
Which structure protects bacteria from phagocytosis?
- A. Flagella
- B. Capsule
- C. Endospore
- D. Pili
Correct Answer: B
Rationale: The correct answer is B: Capsule. Capsules are a protective layer outside the bacterial cell wall that helps bacteria evade phagocytosis by immune cells. The capsule inhibits phagocytic cells from engulfing the bacteria, making it difficult for them to be recognized and destroyed.
A: Flagella - Flagella are not involved in protecting bacteria from phagocytosis. They are responsible for bacterial movement.
C: Endospore - Endospores are dormant, resistant structures formed by some bacteria in response to harsh conditions. They do not directly protect against phagocytosis.
D: Pili - Pili are hair-like structures used for adhesion and conjugation, not for protection against phagocytosis.
Rotaviruses:
- A. The NSP4 nonstructural protein of rotaviruses acts in a toxic-like manner.
- B. Disease can be significant in infants and adults
- C. Cannot survive the acidic environment in the stomach
- D. Prevents the absorption of water, but do not cause a net secretion of water and loss of ions
Correct Answer: A
Rationale: The correct answer is A because the NSP4 nonstructural protein of rotaviruses indeed acts in a toxic-like manner by disrupting calcium homeostasis, leading to diarrhea. Choice B is incorrect as rotaviruses can cause significant disease in infants, but not typically in adults. Choice C is incorrect as rotaviruses are resistant to stomach acid. Choice D is incorrect as rotaviruses cause a net secretion of water and loss of ions, contributing to diarrhea.
A patient with a sore throat and fever had a throat smear stained with Gram's method, revealing Gram-positive cocci in chains. What is the most likely causative agent?
- A. Streptococcus pyogenes
- B. Staphylococcus aureus
- C. Neisseria gonorrhoeae
- D. Enterococcus faecalis
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pyogenes. This bacterium is known to cause sore throat and fever, commonly referred to as strep throat. Gram's stain showing Gram-positive cocci in chains is characteristic of Streptococcus species. Streptococcus pyogenes is a beta-hemolytic bacterium that forms chains and is a common cause of bacterial pharyngitis. Staphylococcus aureus (B) is a Gram-positive cocci that forms clusters, not chains. Neisseria gonorrhoeae (C) is a Gram-negative diplococcus and is not associated with sore throat. Enterococcus faecalis (D) is a Gram-positive cocci that can cause infections but is not typically associated with sore throat.
DNA replication occurs in which phase of the cell cycle?
- A. G phase
- B. Prophase
- C. Metaphase
- D. S phase
Correct Answer: D
Rationale: The correct answer is D: S phase. During the S phase of the cell cycle, DNA replication takes place to ensure each daughter cell receives a complete set of genetic material. This phase is characterized by the synthesis of new DNA strands. In contrast, choices A, B, and C (G phase, Prophase, Metaphase) are not associated with DNA replication. The G phase is a period of cell growth, Prophase is the initial stage of mitosis, and Metaphase is when chromosomes align. Therefore, the S phase is the specific stage where DNA replication occurs, making it the correct answer.
A wound culture revealed Gram-negative rods that are lactose non-fermenters. The bacteria were isolated from a patient with a deep tissue infection. 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 a lactose non-fermenter commonly associated with deep tissue infections. It is an opportunistic pathogen known for its ability to cause infections in immunocompromised individuals. P. aeruginosa is often resistant to multiple antibiotics and can form biofilms, making it difficult to treat.
Summary of why other choices are incorrect:
B: Escherichia coli is a Gram-negative rod that ferments lactose and is commonly found in the gastrointestinal tract. It is not typically associated with deep tissue infections.
C: Salmonella typhi is a Gram-negative rod that causes typhoid fever, primarily affecting the gastrointestinal system, not deep tissue infections.
D: Shigella dysenteriae is a Gram-negative rod that causes bacillary dysentery, which primarily affects the gastrointestinal tract and does not typically cause deep tissue infections.