Microbiology An Evolving Science Test Bank

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A patient with probable liver abscess was delivered to a surgical department. The patient for a long time had been on an assignment in an African country and had recurrent cases of gastrointestinal disturbance. What protozoan disease can it be?

  • A. Toxoplasmosis
  • B. Leishmaniasis
  • C. Malaria
  • D. Amebiasis
Correct Answer: D

Rationale: The correct answer is D: Amebiasis. The patient's symptoms of gastrointestinal disturbance and liver abscess are indicative of an infection with Entamoeba histolytica, the protozoan parasite responsible for amebiasis. The patient's travel history to an African country also increases the likelihood of contracting this disease, as it is more prevalent in tropical regions. Toxoplasmosis (A) is primarily associated with exposure to cat feces, Leishmaniasis (B) is transmitted through sandfly bites, and Malaria (C) is caused by Plasmodium parasites transmitted through mosquito bites. Therefore, these options are incorrect given the patient's presentation and travel history.

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A child with fever and a sore throat had a Gram-stained smear revealing Gram-positive cocci in chains. The bacteria were beta-hemolytic. What is the likely causative agent?

  • A. Streptococcus pyogenes
  • B. Streptococcus pneumoniae
  • C. Staphylococcus aureus
  • D. Enterococcus faecalis
Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. The presence of Gram-positive cocci in chains suggests a streptococcal infection. Beta-hemolysis indicates the production of a hemolysin that lyses red blood cells, a characteristic of Streptococcus pyogenes. This bacterium is known to cause strep throat and can present with fever and sore throat.

Summary:
- B: Streptococcus pneumoniae is a common cause of pneumonia but typically appears as lancet-shaped cocci, not in chains.
- C: Staphylococcus aureus is a gram-positive cocci in clusters, not chains, and is not typically beta-hemolytic.
- D: Enterococcus faecalis is a gram-positive cocci that are part of the normal gut flora and are not typically beta-hemolytic or found in chains.

Enzymatic reactions can be expressed in which of the following chemical notations?

  • A. S + P = E
  • B. P + P = E
  • C. E + S = P
  • D. S + S = P
Correct Answer: C

Rationale: The correct answer is C: E + S = P. This notation represents the interaction between an enzyme (E) and a substrate (S) resulting in a product (P). Enzymes facilitate chemical reactions by binding to substrates and converting them into products. Choice A is incorrect because it does not include the enzyme in the reaction. Choice B is incorrect as it involves two substrates binding to the enzyme, not a substrate converting to a product. Choice D is incorrect as it shows two substrates reacting to form a product without involvement of an enzyme. Thus, choice C accurately represents the process of enzymatic reactions involving enzymes, substrates, and products.

Which of the following bacteria is responsible for causing the disease tetanus?

  • A. Clostridium tetani
  • B. Clostridium perfringens
  • C. Streptococcus pyogenes
  • D. Escherichia coli
Correct Answer: A

Rationale: The correct answer is A: Clostridium tetani. This bacterium is responsible for causing tetanus due to its production of tetanus toxin. Clostridium perfringens (B) causes gas gangrene, Streptococcus pyogenes (C) causes strep throat and skin infections, and Escherichia coli (D) is a common gut bacteria that can cause food poisoning but not tetanus.

Which of the following can be used for specific prophylaxis of pertussis?

  • A. Pertussis toxoid
  • B. Killed vaccine
  • C. Wide-spectrum antibiotics
  • D. None of the above
Correct Answer: A

Rationale: The correct answer is A: Pertussis toxoid. This is because pertussis toxoid is a component of the pertussis vaccine, which provides specific prophylaxis against pertussis by stimulating the immune system to produce antibodies against the bacteria causing the disease. Choice B, killed vaccine, is incorrect as it does not specify pertussis toxoid. Choice C, wide-spectrum antibiotics, is incorrect as antibiotics are used for treatment, not prophylaxis. Choice D, None of the above, is incorrect as pertussis toxoid is specifically used for prophylaxis of pertussis.

Microscopy of dental plaque revealed unicellular organisms. Their cytoplasm had two distinct layers, barely visible core, wide pseudopodia. The patient is most likely to have:

  • A. Entamoeba gingivalis
  • B. Entamoeba histolytica
  • C. Lamblia
  • D. Trichomonas tenax
Correct Answer: D

Rationale: The correct answer is D: Trichomonas tenax. Trichomonas tenax is a flagellated protozoan that is commonly found in the oral cavity, specifically in dental plaque. The description provided in the question matches the characteristics of Trichomonas tenax, such as unicellular structure, distinct layers in the cytoplasm, wide pseudopodia, and barely visible core. Entamoeba gingivalis (choice A) and Entamoeba histolytica (choice B) are amoebas, not flagellated protozoa, and they do not exhibit the characteristics described in the question. Lamblia (choice C) is also an incorrect choice as it is a different type of protozoan that does not match the description provided.

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