Nokea
In order to accurately identify etiology of peptic ulcer disease, polymerase chain reaction (PCR) analysis was performed on gastric biopsy specimen taken from 47-year-old patient. Eventually, the test result was positive for H. pylori. Which of the following was most likely detected in PCR analysis?
- A. Bacterial DNA
- B. Bacterial toxin
- C. H. pylori bacterium itself
- D. Bacterial enzymes – urease and catalase
Correct Answer: A
Rationale: The correct answer is A: Bacterial DNA. PCR analysis detects specific DNA sequences, so a positive result for H. pylori indicates the presence of the bacterial DNA in the gastric biopsy specimen. This method identifies the genetic material of the bacterium, not the bacterium itself (choice C) or its toxins (choice B). Additionally, PCR does not directly detect bacterial enzymes (choice D) but rather focuses on genetic material for accurate identification. Therefore, in this case, the detection of H. pylori in the PCR analysis points to the presence of bacterial DNA, confirming the etiology of peptic ulcer disease.
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The polymerase chain reaction CAN NOT be applied:
- A. To prove latent infection
- B. For rapid diagnosis of infectious diseases
- C. To determine the antibiotic susceptibility of microorganisms
- D. To demonstrate DNA and RNA molecule
Correct Answer: C
Rationale: The correct answer is C: To determine the antibiotic susceptibility of microorganisms. PCR is not suitable for determining antibiotic susceptibility as it is a technique used to amplify DNA/RNA, not to test for antibiotic resistance. To prove latent infection (A), PCR can be used to detect low levels of pathogens. For rapid diagnosis of infectious diseases (B), PCR is commonly used due to its sensitivity and specificity. To demonstrate DNA and RNA molecules (D), PCR is ideal as it can amplify and detect specific sequences. Therefore, choice C is incorrect as PCR is not designed for determining antibiotic susceptibility.
Which of the following scientists performed the first vaccination against smallpox?
- A. Pasteur
- B. Jenner
- C. Semmelweis
- D. Koch
Correct Answer: B
Rationale: The correct answer is B: Jenner. Edward Jenner performed the first vaccination against smallpox in 1796 by using cowpox virus to immunize individuals. He observed that milkmaids who had contracted cowpox did not get smallpox, leading to the development of the smallpox vaccine. Pasteur is known for germ theory, Semmelweis for handwashing in healthcare, and Koch for identifying the causative agents of diseases. However, none of them performed the first smallpox vaccination like Jenner.
Which of the following is a major characteristic of Gram-negative bacteria?
- A. Thick peptidoglycan layer
- B. Outer membrane with lipopolysaccharides
- C. Absence of a cell wall
- D. Presence of teichoic acids
Correct Answer: B
Rationale: The correct answer is B: Outer membrane with lipopolysaccharides. Gram-negative bacteria have an outer membrane that contains lipopolysaccharides, which play a role in pathogenicity and resistance to certain antibiotics. This outer membrane is a distinguishing feature of Gram-negative bacteria, as opposed to Gram-positive bacteria that have a thick peptidoglycan layer. Choices A, C, and D are incorrect because Gram-negative bacteria have a thin peptidoglycan layer, do have a cell wall (although it is different from Gram-positive bacteria), and do not contain teichoic acids.
An outbreak of food poisoning was recorded in an urban settlement. The illness was diagnosed as botulism on the grounds of clinical presentations. What foodstuffs should be chosen for analysis in the first place in order to confirm the diagnosis?
- A. Tinned food
- B. Potatoes
- C. Pasteurized milk
- D. Boiled meat
Correct Answer: A
Rationale: The correct answer is A: Tinned food. Botulism is often caused by the botulinum toxin produced by the bacterium Clostridium botulinum, which can be present in improperly canned foods. Analyzing tinned food allows for direct detection of the toxin or bacteria, confirming the diagnosis. Potatoes, pasteurized milk, and boiled meat are less likely sources of botulism compared to tinned food, making them less suitable for initial analysis in this case.
A 16-year-old boy from the rural area entered the technical school. During a regular Mantoux test, it turned out that this boy had a negative reaction. What tactics should the doctor choose as the most rational in this case?
- A. Repeat the test in a month
- B. Serodiagnosis of tuberculosis
- C. Urgent isolation of the boy from his groupmates
- D. BCG vaccination
Correct Answer: D
Rationale: The correct answer is D: BCG vaccination. BCG vaccination is recommended for individuals with a negative Mantoux test result, especially in countries where tuberculosis is prevalent. This vaccination can help provide protection against tuberculosis.
Choice A is incorrect because repeating the Mantoux test in a month is unnecessary since the boy already had a negative reaction.
Choice B is incorrect as serodiagnosis of tuberculosis is not the first-line approach for diagnosis, especially in this scenario.
Choice C is incorrect because urgent isolation is not necessary based solely on the Mantoux test result. Isolation is typically reserved for individuals with active tuberculosis.