A stool sample from a patient with chronic diarrhea revealed cysts with four nuclei. What is the most likely causative agent?
- A. Entamoeba histolytica
- B. Giardia lamblia
- C. Balantidium coli
- D. Trichomonas hominis
Correct Answer: A
Rationale: The correct answer is A: Entamoeba histolytica. This is because it is a protozoan parasite known to cause amoebic dysentery, presenting with chronic diarrhea and cysts with four nuclei in the stool sample. Giardia lamblia (B) causes giardiasis with trophozoites and cysts with two nuclei. Balantidium coli (C) is a ciliated parasite causing dysentery with large trophozoites. Trichomonas hominis (D) is a non-pathogenic flagellate often found in the human intestine. Thus, based on the specific characteristics of the cysts and clinical presentation, Entamoeba histolytica is the most likely causative agent.
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Bacteria that have a single polar flagellum at one end are referred to as:
- A. monotrichous
- B. monotrichous
- C. amphitrichous
- D. peritrichous
Correct Answer: B
Rationale: Step-by-step rationale:
1. Monotrichous means having a single flagellum at one end.
2. The term "polar" indicates that the flagellum is located at one end of the bacterium.
3. Therefore, bacteria with a single polar flagellum are referred to as monotrichous.
4. Choice A is a typo, as it is the same as the correct answer B.
Summary:
- Choice A is a typo, as it duplicates the correct answer.
- Choice C, amphitrichous, refers to bacteria with a flagellum at each end.
- Choice D, peritrichous, describes bacteria with flagella distributed over the entire surface.
Which bacteria are capable of forming spores to survive in harsh environments?
- A. Bacillus anthracis
- B. Clostridium botulinum
- C. Both A and B
- D. None of the above
Correct Answer: C
Rationale: The correct answer is C (Both A and B) because both Bacillus anthracis and Clostridium botulinum are capable of forming spores to survive in harsh environments. Bacillus anthracis causes anthrax and forms spores that can survive extreme conditions. Clostridium botulinum causes botulism and also forms spores for survival. Option A (Bacillus anthracis) and Option B (Clostridium botulinum) are incorrect on their own because they only represent one of the bacteria capable of forming spores. Option D (None of the above) is incorrect because it disregards the fact that both bacteria can form spores.
A patient with chronic diarrhea had stool microscopy revealing flagellated protozoa with two nuclei. What is the most likely causative agent?
- A. Giardia lamblia
- B. Entamoeba histolytica
- C. Trichomonas vaginalis
- D. Balantidium coli
Correct Answer: A
Rationale: The correct answer is A: Giardia lamblia. Giardia lamblia is a flagellated protozoan with two nuclei found in the stool. It commonly causes chronic diarrhea. The other choices are incorrect because B: Entamoeba histolytica causes dysentery, not chronic diarrhea; C: Trichomonas vaginalis is a sexually transmitted infection, not typically found in stool; D: Balantidium coli is a ciliated protozoan, not flagellated.
The specific binding of HIV to the CD4 surface molecules of the target cells is brought about by:
- A. Gp120
- B. Gp41
- C. Gp32
- D. Gp55
Correct Answer: A
Rationale: The correct answer is A: Gp120. Gp120 is a glycoprotein on the surface of the HIV virus that specifically binds to the CD4 receptor on target cells. This binding is essential for the virus to enter the host cell and initiate the infection process. Gp41 is another glycoprotein on the virus that helps with membrane fusion, not binding to CD4. Gp32 and Gp55 are not involved in the specific binding of HIV to CD4 molecules. So, A is correct as it directly plays a key role in the initial attachment of HIV to target cells.
The basic method for routine mumps diagnosis is;
- A. PCR
- B. Isolation on cell cultures
- C. ELISA
- D. Immunofluorescence method
Correct Answer: B
Rationale: The correct answer is B: Isolation on cell cultures. This method is the gold standard for routine mumps diagnosis as it involves isolating the virus in cell cultures to confirm the presence of the mumps virus. PCR (choice A) is used for detecting viral RNA, not for routine diagnosis. ELISA (choice C) detects antibodies, not the virus itself. Immunofluorescence method (choice D) is used for visualizing viral antigens but is not as reliable as isolating the virus in cell cultures for diagnosis.