Nokea
Which of the following bacteria produces a neurotoxin that causes botulism?
- A. Clostridium botulinum
- B. Clostridium tetani
- C. Escherichia coli
- D. Staphylococcus aureus
Correct Answer: A
Rationale: The correct answer is A: Clostridium botulinum. Clostridium botulinum produces the neurotoxin that causes botulism. This bacterium thrives in anaerobic conditions and contaminated food. The neurotoxin blocks acetylcholine release at the neuromuscular junction, leading to muscle paralysis. Choices B, C, and D are incorrect because Clostridium tetani causes tetanus, Escherichia coli can cause food poisoning but not botulism, and Staphylococcus aureus produces enterotoxins causing food poisoning, not botulism.
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Lysozyme acts on the bacterial:
- A. cytoplasm
- B. cell wall
- C. nucleus
- D. capsule
Correct Answer: B
Rationale: The correct answer is B: cell wall. Lysozyme is an enzyme that targets the cell wall of bacteria by breaking down the peptidoglycan layer, leading to bacterial cell lysis. This action disrupts the structural integrity of the bacteria, ultimately causing their death. Choices A, C, and D are incorrect because lysozyme does not target the cytoplasm, nucleus, or capsule of bacteria. The primary function of lysozyme is to act on the cell wall, making option B the correct answer in this context.
A patient with pneumonia had sputum cultured on Endo agar, revealing red colonies. The bacteria were Gram-negative rods. What is the most likely causative agent?
- A. Escherichia coli
- B. Klebsiella pneumoniae
- C. Pseudomonas aeruginosa
- D. Proteus mirabilis
Correct Answer: A
Rationale: Rationale for correct answer (A: Escherichia coli):
1. Endo agar selects for Gram-negative bacteria.
2. Red colonies on Endo agar indicate lactose fermentation, characteristic of E. coli.
3. E. coli is a common cause of pneumonia, especially in immunocompromised patients.
Summary of why other choices are incorrect:
- B: Klebsiella pneumoniae: Typically forms mucoid colonies on agar.
- C: Pseudomonas aeruginosa: Produces characteristic greenish-blue colonies on agar.
- D: Proteus mirabilis: Does not typically ferment lactose, so would not produce red colonies on Endo agar.
Gram staining is used to differentiate bacteria based on:
- A. size and shape
- B. presence of flagella
- C. cell wall composition
- D. genetic material
Correct Answer: C
Rationale: The correct answer is C: cell wall composition. Gram staining differentiates bacteria based on the structure of their cell walls. It classifies bacteria into Gram-positive (thick peptidoglycan layer) and Gram-negative (thin peptidoglycan layer). This differentiation is crucial for identifying bacterial species and guiding treatment choices. Size and shape (choice A) are not specific to Gram staining. Presence of flagella (choice B) is related to bacterial motility, not Gram staining. Genetic material (choice D) is not directly assessed by Gram staining. Overall, the unique composition of the cell wall is the key factor in distinguishing bacteria through Gram staining.
A patient with a severe case of pneumonia had sputum stained using the Gram method. The smear revealed Gram-positive cocci arranged in pairs with a capsule. What is the most likely causative agent?
- A. Streptococcus pneumoniae
- B. Staphylococcus aureus
- C. Klebsiella pneumoniae
- D. Enterococcus faecalis
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is a common cause of pneumonia and is characterized by being Gram-positive cocci arranged in pairs with a capsule, as described in the question. The presence of a capsule is a key characteristic of Streptococcus pneumoniae, distinguishing it from the other choices. Staphylococcus aureus (B) is a Gram-positive cocci, but it typically forms clusters, not pairs. Klebsiella pneumoniae (C) is a Gram-negative rod, not a Gram-positive cocci. Enterococcus faecalis (D) is a Gram-positive cocci, but it does not typically present with a capsule in the same way Streptococcus pneumoniae does.
The net gain of ATP molecules after the breakdown of one glucose molecule in glycolysis is
- A. 1
- B. 2
- C. 3
- D. 4
Correct Answer: B
Rationale: The correct answer is B (2). During glycolysis, one glucose molecule is broken down into two molecules of pyruvate. In this process, a net gain of 2 ATP molecules is produced through substrate-level phosphorylation. Specifically, ATP is generated during the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate and during the conversion of phosphoenolpyruvate to pyruvate. The other choices are incorrect because the net gain of ATP molecules in glycolysis is not 1, 3, or 4; it is 2 based on the specific enzymatic reactions involved in the pathway.