Nokea
Which bacteria is known for producing a neurotoxin that causes botulism?
- A. Clostridium botulinum
- B. Clostridium tetani
- C. Streptococcus pneumoniae
- D. Escherichia coli
Correct Answer: A
Rationale: Step-by-step rationale:
1. Clostridium botulinum is known for producing the neurotoxin causing botulism.
2. Botulinum toxin paralyzes muscles, leading to symptoms of botulism.
3. Clostridium tetani produces tetanus toxin causing muscle rigidity, not botulism.
4. Streptococcus pneumoniae causes pneumonia, not botulism.
5. Escherichia coli can cause food poisoning, but not botulism.
Summary:
Choice A is correct (Clostridium botulinum) due to its association with botulism and neurotoxin production. Choices B, C, and D are incorrect as they are associated with different diseases and toxins.
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A wound infection culture revealed Gram-positive cocci in clusters. The bacteria were catalase-positive and coagulase-positive. What is the most likely causative agent?
- A. Staphylococcus aureus
- B. Staphylococcus epidermidis
- C. Streptococcus pyogenes
- D. Enterococcus faecalis
Correct Answer: A
Rationale: The correct answer is A: Staphylococcus aureus. This bacterium is characterized by Gram-positive cocci in clusters, catalase-positive, and coagulase-positive. Staphylococcus aureus is a common pathogen causing wound infections due to its ability to produce toxins and enzymes. Staphylococcus epidermidis (B) is catalase-positive but coagulase-negative, making it less likely to cause infections. Streptococcus pyogenes (C) is catalase-negative and typically causes streptococcal infections, not wound infections. Enterococcus faecalis (D) is catalase-negative and typically associated with urinary tract infections. Thus, Staphylococcus aureus is the most likely causative agent based on the given characteristics.
Which bacteria are responsible for causing the disease known as leprosy?
- A. Mycobacterium leprae
- B. Escherichia coli
- C. Clostridium botulinum
- D. Staphylococcus aureus
Correct Answer: A
Rationale: The correct answer is A: Mycobacterium leprae. This bacterium is responsible for causing leprosy because it has a unique ability to infect the skin, nerves, and mucous membranes. It is an acid-fast bacillus that multiplies very slowly, leading to a chronic infection. Clostridium botulinum (choice C) causes botulism, Escherichia coli (choice B) causes various gastrointestinal infections, and Staphylococcus aureus (choice D) causes skin infections and other diseases, but none of these bacteria are associated with leprosy.
The one-way transfer of genetic material from a donor cell to a recipient cell by direct cell-to-cell contact is:
- A. transformation
- B. transduction
- C. replication
- D. conjugation
Correct Answer: D
Rationale: Conjugation involves direct cell-to-cell contact for the transfer of genetic material, typically through a pilus. This process is well-documented in bacterial genetics. Transformation (A) involves uptake of free DNA from the environment. Transduction (B) is genetic transfer by a viral vector. Replication (C) is the process of producing identical copies of DNA or RNA. Therefore, the correct answer is D (conjugation) as it specifically refers to the one-way transfer of genetic material through direct cell-to-cell contact.
A fecal smear from a patient with severe diarrhea revealed motile Gram-negative rods with a comma shape. What is the likely causative agent?
- A. Vibrio cholerae
- B. Shigella dysenteriae
- C. Salmonella typhi
- D. Escherichia coli
Correct Answer: A
Rationale: The correct answer is A: Vibrio cholerae. This bacterium is the likely causative agent because it is known to cause severe diarrhea, and it is characterized by its motile, comma-shaped Gram-negative rods. Vibrio cholerae produces cholera toxin, leading to profuse watery diarrhea. Shigella dysenteriae causes dysentery with bloody diarrhea, Salmonella typhi causes typhoid fever, and Escherichia coli can cause various types of diarrhea but typically does not have a comma shape.
What are the two main targets currently used in anti-HIV therapy?
- A. Reverse transcriptase and something integrase
- B. Reverse transcriptase and protease
- C. Protease and integrase
- D. Viral glycoproteins gp120 and gp41
Correct Answer: B
Rationale: The correct answer is B: Reverse transcriptase and protease. Reverse transcriptase converts viral RNA into DNA, a crucial step in viral replication. Protease is responsible for cleaving viral polyproteins into functional proteins. Targeting both enzymes disrupts viral replication. Choice A is incorrect as integrase is not a main target in current therapy. Choice C is incorrect because protease is targeted along with reverse transcriptase, not integrase. Choice D is incorrect as targeting viral glycoproteins is not a main strategy in anti-HIV therapy.