Nokea
A child with fever and swollen lymph nodes had a Gram-stained smear revealing Gram-negative rods with a safety pin appearance. What is the causative agent?
- A. Yersinia pestis
- B. Francisella tularensis
- C. Brucella abortus
- D. Clostridium botulinum
Correct Answer: A
Rationale: The correct answer is A: Yersinia pestis. This bacterium causes the plague, which presents with fever and swollen lymph nodes. The safety pin appearance on Gram stain is characteristic of Yersinia pestis.
B: Francisella tularensis causes tularemia, which presents differently and does not show safety pin appearance on Gram stain.
C: Brucella abortus causes brucellosis, which does not typically present with the same symptoms as described in the question.
D: Clostridium botulinum causes botulism, which does not show safety pin appearance on Gram stain and does not typically present with fever and swollen lymph nodes.
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Sterilization destroys all microorganisms including:
- A. vegetative cells only
- B. viruses only
- C. spores
- D. protozoa only
Correct Answer: C
Rationale: Sterilization refers to the complete elimination of all microorganisms, including their spores, which are the most resistant form of microbial life. Spores have a tough outer coating that protects them from harsh conditions, making them more difficult to destroy compared to vegetative cells, viruses, and protozoa. Therefore, the correct answer is C because sterilization targets and eliminates all forms of microorganisms, including spores. Choices A, B, and D are incorrect because sterilization goes beyond just targeting vegetative cells, viruses, or protozoa; it aims to eliminate all microorganisms present.
Bacteria that use organic compounds as the source of both carbon and energy are referred to as:
- A. photoautotrophs
- B. chemoautotrophs
- C. photoheterotrophs
- D. chemoheterotrophs
Correct Answer: D
Rationale: The correct answer is D: chemoheterotrophs. Chemoheterotrophs use organic compounds as both their carbon source and energy source. They obtain energy by breaking down organic molecules through cellular respiration. Photoautotrophs (A) use light energy to produce organic compounds, chemoautotrophs (B) use inorganic compounds for energy, and photoheterotrophs (C) use light energy but require organic compounds as a carbon source. Therefore, chemoheterotrophs best describe bacteria that obtain both carbon and energy from organic compounds.
The process in which bacteria take up foreign DNA from the environment is called:
- A. Transformation
- B. Transduction
- C. Conjugation
- D. Binary fission
Correct Answer: A
Rationale: The correct answer is A: Transformation. During transformation, bacteria take up foreign DNA from the environment and incorporate it into their own genetic material. This process allows for genetic diversity and adaptation. Transduction (B) involves transfer of DNA via a virus, conjugation (C) involves direct transfer of DNA between bacterial cells, and binary fission (D) is a form of asexual reproduction in bacteria. Transformation is the only process specifically related to bacteria taking up foreign DNA.
Which of these is not a factor counteracting the mechanisms of the immune system:
- A. Antigenic heterogeneity
- B. Antigenic mimicry
- C. Synthesis of IgA proteases
- D. Hyaluronidase synthesis
Correct Answer: D
Rationale: The correct answer is D: Hyaluronidase synthesis. Hyaluronidase is an enzyme produced by some pathogens to break down hyaluronic acid in the extracellular matrix, aiding their spread. This action does not directly counteract the immune system's mechanisms. Antigenic heterogeneity and mimicry can evade immune recognition. IgA proteases degrade IgA antibodies, impairing mucosal immunity. Therefore, D is the only choice not directly involved in counteracting the immune system.
Which organism produces a toxin that blocks neuromuscular transmission in cholinergic motor neurons:
- A. Shigella dysenteriae
- B. Clostridium tetani
- C. Corynebacterium diphtheria
- D. Clostridium botulinum
Correct Answer: D
Rationale: The correct answer is D: Clostridium botulinum. This bacterium produces botulinum toxin, which blocks neuromuscular transmission by inhibiting the release of acetylcholine at the neuromuscular junction. This leads to muscle weakness and paralysis. Shigella dysenteriae (A) causes dysentery but does not affect neuromuscular transmission. Clostridium tetani (B) produces tetanus toxin, which affects inhibitory neurons in the spinal cord, leading to muscle spasm. Corynebacterium diphtheriae (C) produces diphtheria toxin, which affects protein synthesis in cells, not neuromuscular transmission.