Nokea
Which of the following bacteria produce a toxin that inhibits protein synthesis?
- A. Shigella dysenteriae
- B. Escherichia coli
- C. Clostridium tetani
- D. Staphylococcus aureus
Correct Answer: A
Rationale: The correct answer is A: Shigella dysenteriae. This bacterium produces Shiga toxin, which inhibits protein synthesis by inactivating the ribosomes. Shigella dysenteriae is known to cause severe gastrointestinal infections.
Choice B: Escherichia coli typically does not produce toxins that inhibit protein synthesis. E. coli strains may produce toxins that cause diarrhea.
Choice C: Clostridium tetani produces tetanospasmin toxin, which affects the nervous system but does not inhibit protein synthesis.
Choice D: Staphylococcus aureus produces toxins like enterotoxins and exotoxins but these toxins do not directly inhibit protein synthesis.
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According to their optimal growth temperatures, microorganisms are divided into:
- A. Thermophilic and thermophobic
- B. Psychophilic and psychophobic
- C. Psychophilic, mesophilic, thermophilic
- D. Thermophilic, thermophobic, mesophobic
Correct Answer: C
Rationale: Rationale:
1. Psychrophilic: Grow best in cold temperatures
2. Mesophilic: Grow best in moderate temperatures
3. Thermophilic: Grow best in high temperatures
- Choice A is incorrect as "thermophobic" is not a recognized term.
- Choice B is incorrect as "psychophobic" is not a recognized term.
- Choice D is incorrect as "mesophobic" is not a recognized term.
Which type of bacteria have an outer membrane containing lipopolysaccharides (LPS)?
- A. Gram-positive bacteria
- B. Gram-negative bacteria
- C. Both Gram-positive and Gram-negative bacteria
- D. Neither Gram-positive nor Gram-negative bacteria
Correct Answer: B
Rationale: The correct answer is B: Gram-negative bacteria. Gram-negative bacteria have an outer membrane containing lipopolysaccharides (LPS). In the Gram staining technique, these bacteria appear pink/red due to the thin peptidoglycan layer, which allows the crystal violet stain to be washed out, revealing the safranin counterstain. Gram-positive bacteria (choice A) have a thick peptidoglycan layer but lack an outer membrane with LPS. Choice C is incorrect since only Gram-negative bacteria possess LPS in their outer membrane. Choice D is incorrect as all bacteria can be classified as either Gram-positive or Gram-negative based on their cell wall structure.
Psychrophiles are also referred to as:
- A. cryophiles
- B. thermophiles
- C. mesophiles
- D. psychrotrophs
Correct Answer: A
Rationale: The correct answer is A: cryophiles. Psychrophiles are microorganisms that thrive in cold temperatures. The prefix "cryo-" means cold, which accurately describes the environment in which these organisms grow. Choice B, thermophiles, are organisms that thrive in high temperatures. Choice C, mesophiles, grow best at moderate temperatures. Choice D, psychrotrophs, are organisms that can grow at refrigeration temperatures but have an optimal growth temperature range different from psychrophiles.
Exotoxins are:
- A. Produced in the microbe cell and then released in the neighbouring...
- B. Produced in the microbe cell and acting into the same cell
- C. Part of the microbe cell and acting into the same cell
- D. Part of the microbe cell, are released outside after cell lysis
Correct Answer: A
Rationale: Exotoxins are proteins produced inside the microbe cell and then released outside the cell to exert their toxic effects on neighboring cells or tissues. This is why choice A is correct. Choices B and C are incorrect because exotoxins are not meant to act within the same cell they are produced in. Choice D is incorrect because exotoxins are usually released without causing cell lysis; they are secreted by the microbe actively rather than being leaked out due to cell damage.
The key diagnostic feature of Corynebacterium diphtheriae is:
- A. formation of spores
- B. presence of metachromatic granules
- C. production of coagulase
- D. beta-hemolysis on blood agar
Correct Answer: B
Rationale: The correct answer is B: presence of metachromatic granules. This is because Corynebacterium diphtheriae is known for containing metachromatic granules, which are characteristic of this species. These granules can be observed under a microscope and aid in the identification of the bacteria.
Explanation of other choices:
A: formation of spores - Corynebacterium diphtheriae does not form spores. Spore formation is more commonly seen in bacteria such as Bacillus and Clostridium species.
C: production of coagulase - Coagulase production is a characteristic of Staphylococcus aureus, not Corynebacterium diphtheriae.
D: beta-hemolysis on blood agar - Corynebacterium diphtheriae does not exhibit beta-hemolysis on blood agar. This type of hemolysis is more typical of Streptococcus pyogenes.