Nokea
Viruses are characterised by:
- A. They have only one type of nucleic acid
- B. Their extracellular form is referred as “viroidâ€
- C. They are optional intracellular parasites
- D. Their size is measured in micrometers
Correct Answer: A
Rationale: Step 1: Viruses can have either DNA or RNA, not both, hence they have only one type of nucleic acid.
Step 2: The extracellular form of viruses is called virion, not viroid.
Step 3: Viruses are obligate intracellular parasites, meaning they rely on host cells for replication.
Step 4: Viruses are measured in nanometers, not micrometers.
Therefore, the correct answer is A.
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Which of the following bacteria produces a toxin that causes botulism?
- A. Clostridium botulinum
- B. Clostridium tetani
- C. Staphylococcus aureus
- D. Escherichia coli
Correct Answer: A
Rationale: The correct answer is A: Clostridium botulinum. Clostridium botulinum produces the botulinum toxin, which causes botulism. This bacteria thrives in anaerobic environments and can contaminate improperly canned foods. Clostridium tetani causes tetanus, not botulism. Staphylococcus aureus produces enterotoxins causing food poisoning, not botulism. Escherichia coli can cause food poisoning through various toxins, but not botulism. Therefore, the correct choice is Clostridium botulinum as it specifically produces the botulinum toxin responsible for botulism.
How the prepared immunofluorescence slide should be examined?
- A. Under the fluorescence microscope using x100 oil immersion objective
- B. Under light microscope using x100 oil immersion objective
- C. Using electron microscopy
- D. None of the above
Correct Answer: A
Rationale: The correct answer is A because immunofluorescence slides are examined under a fluorescence microscope with a x100 oil immersion objective. This is because immunofluorescence relies on the detection of fluorescently labeled antibodies, which emit light when excited by a specific wavelength. Using a fluorescence microscope allows for visualization of these labeled antibodies at high magnification and resolution, enabling precise examination of cellular structures and protein localization. Choice B is incorrect as light microscopes are not suitable for visualizing fluorescence. Choice C is incorrect as electron microscopes use electrons, not light, for imaging, which is not compatible with immunofluorescence. Choice D is incorrect as there is a specific method for examining immunofluorescence slides.
Which of the following bacteria is known for causing dental caries (cavities)?
- A. Streptococcus mutans
- B. Streptococcus pneumoniae
- C. Bacillus anthracis
- D. Clostridium botulinum
Correct Answer: A
Rationale: Step 1: Streptococcus mutans is known for its ability to produce acids that contribute to the demineralization of tooth enamel, leading to dental caries.
Step 2: Streptococcus pneumoniae is a common cause of respiratory infections, not dental caries.
Step 3: Bacillus anthracis causes anthrax, a serious bacterial infection, not dental caries.
Step 4: Clostridium botulinum causes botulism, a severe form of food poisoning, not dental caries.
Summary: Streptococcus mutans is the correct answer as it is specifically associated with causing dental caries, while the other choices are linked to different diseases.
Which of the following bacteria are associated with foodborne illnesses?
- A. Clostridium botulinum
- B. Salmonella enterica
- C. Escherichia coli
- D. All of the above
Correct Answer: D
Rationale: The correct answer is D, "All of the above." Clostridium botulinum causes botulism, Salmonella enterica causes salmonellosis, and Escherichia coli can cause foodborne illnesses such as E. coli infection. All three bacteria are associated with foodborne illnesses due to contamination of food or water sources. Therefore, selecting "All of the above" is the most appropriate choice as it includes all the bacteria commonly linked to foodborne illnesses. The other choices (A, B, and C) are incorrect because they do not encompass all the bacteria associated with foodborne illnesses as stated above.
A wound culture from a patient with an infected ulcer revealed Gram-positive rods with terminal spores. What is the most likely causative agent?
- A. Clostridium perfringens
- B. Bacillus anthracis
- C. Clostridium tetani
- D. Bacillus cereus
Correct Answer: A
Rationale: Step-by-step rationale:
1. Gram-positive rods with terminal spores suggest Clostridium genus.
2. Terminal spores are characteristic of Clostridium perfringens.
3. C. perfringens is known to cause wound infections.
4. Therefore, the most likely causative agent is Clostridium perfringens.
Summary:
A: Clostridium perfringens is correct due to its characteristic features and association with wound infections.
B: Bacillus anthracis does not typically form terminal spores.
C: Clostridium tetani causes tetanus, not wound infections.
D: Bacillus cereus does not produce terminal spores like Clostridium perfringens.