Nokea
The territory of an old burial ground for animal refuse that hasn't been used for over 50 years is meant for house building. But soil investigation showed the presence of viable spores of a causative agent causing a very dangerous disease. What microorganism might have been preserved in soil for such a long period of time?
- A. Bacillus anthracis
- B. Francisella tularensis
- C. Brucella abortus
- D. Yersinia pestis
Correct Answer: A
Rationale: The correct answer is A: Bacillus anthracis. This bacterium is known to form highly resistant spores that can survive for long periods in soil. Bacillus anthracis causes anthrax, a dangerous disease that can be transmitted to humans and animals. The other choices, Francisella tularensis, Brucella abortus, and Yersinia pestis, do not form spores as resistant as Bacillus anthracis. Therefore, only Bacillus anthracis is likely to have survived in the soil of the old burial ground for animal refuse for over 50 years.
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A 10-year-old child cut his leg with a glass shard, when playing, and was delivered to outpatient department to receive anti-tetanus serum. To prevent development of anaphylactic shock the serum was introduced by Bezredka method. This method of organism hyposensitization is based on the following mechanism:
- A. Stimulation of antigen-specific IgG2
- B. Stimulation of the immunological antigen tolerance
- C. Binding of mast cell-fixed IgE
- D. Blocking of mast cell mediators synthesis
Correct Answer: C
Rationale: The correct answer is C: Binding of mast cell-fixed IgE. The Bezredka method involves introducing small amounts of the antigen to which the individual is allergic, leading to the binding of mast cell-fixed IgE. This process desensitizes the immune system and prevents anaphylactic shock by reducing the release of histamine and other mediators from mast cells.
Rationale:
1. A: Stimulation of antigen-specific IgG2 is incorrect because the Bezredka method primarily targets IgE, not IgG2.
2. B: Stimulation of the immunological antigen tolerance is incorrect as this method aims to block the allergic response rather than induce tolerance.
3. D: Blocking of mast cell mediators synthesis is incorrect because the Bezredka method does not directly inhibit the synthesis of mast cell mediators, but rather blocks their release by binding IgE.
Sanitary bacteriological research on water by the membrane filter method revealed two red colonies on a membrane filter (Endo agar) through which 500 ml of analyzed water were passed. Calculate the coli index and coli titer of the analyzed water:
- A. 4 and 250
- B. 2 and 500
- C. 250 and 4
- D. 500 and 2
Correct Answer: A
Rationale: The correct answer is A: 4 and 250. Coli index is calculated by dividing the number of red colonies by the volume of water analyzed, which gives 2 red colonies / 500 ml = 4. Coli titer is the reciprocal of the coli index, so it is 1 / 4 = 250. This indicates the concentration of coliform bacteria in the water sample. Choices B, C, and D are incorrect as they do not follow the correct calculation steps for determining the coli index and coli titer. B has the correct coli index but incorrect coli titer. C and D have the values reversed, leading to incorrect results.
Which of the following bacteria are capable of forming spores?
- A. Staphylococcus aureus
- B. Clostridium botulinum
- C. Escherichia coli
- D. Neisseria gonorrhoeae
Correct Answer: B
Rationale: The correct answer is B, Clostridium botulinum. This bacterium is capable of forming spores, which are dormant, resistant structures that help bacteria survive harsh conditions. Staphylococcus aureus (A), Escherichia coli (C), and Neisseria gonorrhoeae (D) do not form spores. Staphylococcus aureus is a gram-positive bacterium that does not produce spores. Escherichia coli is a gram-negative bacterium that also does not form spores. Neisseria gonorrhoeae is a gram-negative bacterium and does not have the ability to form spores. Therefore, the only bacteria among the options that can form spores is Clostridium botulinum.
What is the structure of the bacterial cell wall?
- A. Peptidoglycan
- B. Lipopolysaccharides
- C. Phospholipids
- D. Chitin
Correct Answer: A
Rationale: The correct answer is A: Peptidoglycan. Bacterial cell walls are composed of peptidoglycan, a unique macromolecule consisting of sugars and amino acids. This structure provides rigidity and protection to the cell. Lipopolysaccharides are found in the outer membrane of Gram-negative bacteria, not in the cell wall. Phospholipids are the main components of cell membranes, not cell walls. Chitin is a structural polysaccharide found in the cell walls of fungi and some algae, not bacteria.
Bacteria associated with hospital-acquired infections:
- A. Streptococcus pneumoniae
- B. Pseudomonas aeruginosa
- C. Vibrio cholerae
- D. None of the above
Correct Answer: B
Rationale: The correct answer is B: Pseudomonas aeruginosa. This bacterium is commonly associated with hospital-acquired infections due to its ability to survive in hospital environments, resist antibiotics, and infect immunocompromised patients. Streptococcus pneumoniae (choice A) is more commonly associated with community-acquired pneumonia. Vibrio cholerae (choice C) causes cholera, a waterborne disease, and is not typically associated with hospital-acquired infections. Choice D is incorrect because Pseudomonas aeruginosa is indeed associated with hospital-acquired infections.