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A child with diarrhea had stool microscopy revealing 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 pathogen is known to cause amoebic dysentery, characterized by diarrhea with bloody or mucoid stools. The presence of cysts with four nuclei in the stool microscopy is a characteristic feature of Entamoeba histolytica. Other choices are incorrect because Giardia lamblia typically presents with binucleate cysts, Balantidium coli is a ciliated protozoan, and Trichomonas hominis is a non-pathogenic parasite found in the human intestine.
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Bacteriology testing is one of the methods for laboratory diagnostics of diphtheria. To grow the
- A. diphtheriae, it is necessary to know the proper conditions for causative agent cultivation. What nutrient media are optimal for Corynebacterium diphtheriae cultivation?
- B. Sugar meat pepton broth, sugar meat pepton agar
- C. Salt egg yolk agar
- D. Endomedium, Ploskirev medium
Correct Answer: B
Rationale: The correct answer is B: Sugar meat pepton broth, sugar meat pepton agar. These nutrient media are optimal for Corynebacterium diphtheriae cultivation due to their ability to support the growth of this bacterium. Sugar meat pepton broth provides a liquid medium with essential nutrients, while sugar meat pepton agar provides a solid surface for bacterial growth and isolation.
Incorrect choices:
A: Diphtheriae does not require specific conditions for cultivation.
C: Salt egg yolk agar is not commonly used for Corynebacterium diphtheriae.
D: Endomedium and Ploskirev medium are not standard media for diphtheria testing.
How soon do symptoms typically appear after a person is infected with rabies virus
- A. 48 hours
- B. 1 week
- C. 1 month
- D. 1-2 years
Correct Answer: D
Rationale: The correct answer is D: 1-2 years. Rabies has a long incubation period before symptoms appear due to the slow progression of the virus within the body. The virus travels along nerve fibers to the brain, which can take months to years. During this time, the virus replicates and spreads, eventually leading to symptoms. Choices A, B, and C are incorrect as they underestimate the incubation period of rabies. Symptoms typically do not appear as early as 48 hours, 1 week, or 1 month after infection with the rabies virus.
Which type of bacteria can survive in extreme salty environments?
- A. Psychrophiles
- B. Halophiles
- C. Thermophiles
- D. Mesophiles
Correct Answer: B
Rationale: The correct answer is B: Halophiles. Halophiles are bacteria that can survive in extreme salty environments. They have adapted to thrive in high salt concentrations. Psychrophiles (A) thrive in cold temperatures, Thermophiles (C) thrive in high temperatures, and Mesophiles (D) thrive in moderate temperatures. Therefore, they are not adapted to survive in extreme salty environments like Halophiles.
In which of the following GIT infections, the bacteria adhere to the intestine wall and damage the microvilli:
- A. Enteropathogenic E. Coli (EPEC)
- B. Enterohemorrhagic E. Coli (EHEC)
- C. Enterotoxigenic E Coli (ETEC)
- D. Enteroinvasive E Coli (EIEC)
Correct Answer: A
Rationale: The correct answer is A: Enteropathogenic E. Coli (EPEC). EPEC bacteria adhere to the intestine wall using a protein called intimin, leading to microvilli damage. This attachment disrupts the normal absorption function of the intestine.
Summary of why other choices are incorrect:
B: Enterohemorrhagic E. Coli (EHEC) primarily causes bloody diarrhea and does not specifically target microvilli.
C: Enterotoxigenic E. Coli (ETEC) produces toxins that lead to watery diarrhea but does not directly target microvilli.
D: Enteroinvasive E. Coli (EIEC) invades and replicates within intestinal cells, causing inflammatory diarrhea, but does not specifically damage microvilli.
The prokaryotic cell does not possess:
- A. Ribosomes
- B. Endoplasmic reticulum
- C. Chromosome
- D. Peptidoglycan
Correct Answer: B
Rationale: The correct answer is B: Endoplasmic reticulum. Prokaryotic cells lack membrane-bound organelles like the endoplasmic reticulum, which is present in eukaryotic cells. Prokaryotes do possess ribosomes for protein synthesis (A), a chromosome (C) for genetic material, and peptidoglycan (D) in their cell walls. The absence of endoplasmic reticulum is a key characteristic that distinguishes prokaryotic cells from eukaryotic cells.