Nokea
Bacterial endotoxins are:
- A. proteins in the cell wall
- B. secreted into the environment
- C. components of the gram-positive cell wall
- D. components of the gram-negative cell wall
Correct Answer: D
Rationale: The correct answer is D: components of the gram-negative cell wall. Bacterial endotoxins are lipopolysaccharides found in the outer membrane of gram-negative bacteria. They are released upon bacterial cell lysis and can cause severe immune responses.
A: Proteins in the cell wall - This is incorrect because endotoxins are not proteins but rather lipopolysaccharides.
B: Secreted into the environment - Endotoxins are not actively secreted but are released upon cell death or lysis.
C: Components of the gram-positive cell wall - Gram-positive bacteria do not have an outer membrane with lipopolysaccharides, so endotoxins are not found in the gram-positive cell wall.
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Which of the following viruses can cause hemorrhagic cystitis in immunocompromised patients:
- A. EBV
- B. BKV
- C. HSV1
- D. JCV
Correct Answer: B
Rationale: The correct answer is B: BKV. BK virus can cause hemorrhagic cystitis in immunocompromised patients by infecting the urinary tract. It primarily affects the renal tubular epithelial cells, leading to hemorrhagic cystitis. EBV (A) causes infectious mononucleosis, HSV1 (C) causes oral and genital herpes, and JCV (D) causes progressive multifocal leukoencephalopathy, none of which are associated with hemorrhagic cystitis.
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.
A child is presumably ill with diphtheria. A specimen of affected mucous membrane of his pharynx was taken for analysis. The smear was stained and microscopic examination revealed yellow rods with dark blue thickenings on their ends. What structural element of a germ cell was revealed in the detected microorganisms?
- A. Volutin granules
- B. Plasmids
- C. Capsule
- D. Spores
Correct Answer: A
Rationale: The correct answer is A: Volutin granules. Volutin granules are metachromatic granules that stain dark blue with methylene blue or Leishman stain. In diphtheria-causing bacteria, Corynebacterium diphtheriae, these granules are typically seen as yellow rods with dark blue thickenings on their ends when stained. Volutin granules are storage inclusions composed of polymetaphosphate that serve as an energy reserve for the bacteria. The presence of these granules in the detected microorganisms indicates the characteristic feature of Corynebacterium diphtheriae.
Summary of other choices:
B: Plasmids are extrachromosomal DNA molecules that are not typically visible on stained smears.
C: Capsules are outer protective layers that are not visible on stained smears.
D: Spores are reproductive structures formed by certain bacteria, not typically seen in Corynebacterium diphtheriae.
The most common causative agent of nosocomial infections are:
- A. E.Coli, S. aureus, L. monocytogenes
- B. E. Coli, S. aureus, Enterobacteriacae
- C. S. epidermidis, E.Coli, Enterococcus spp.
- D. None of the above
Correct Answer: C
Rationale: Rationale: Choice C is correct because Staphylococcus epidermidis, Escherichia coli, and Enterococcus spp. are common causative agents of nosocomial infections due to their presence on the skin, in the gut, and in healthcare settings. S. aureus and L. monocytogenes (Choice A) are also important pathogens but are less common in nosocomial infections. Enterobacteriaceae (Choice B) are a large family of bacteria that can cause infections but are not as commonly associated with nosocomial infections compared to the organisms in Choice C. The correct answer (Choice C) encompasses pathogens commonly found in healthcare settings, making it the most suitable option.
Diatoms, major components of marine phytoplankton, belong to:
- A. Chrysophyta
- B. Rhodophyta
- C. Chlorophyta
- D. Phaeophyta
Correct Answer: A
Rationale: The correct answer is A: Chrysophyta. Diatoms are classified under the division Chrysophyta due to their unique characteristics, such as possessing a cell wall made of silica (siliceous frustule) and containing chlorophyll a and c for photosynthesis. Chrysophyta includes golden-brown algae, which diatoms are a part of. Rhodophyta (B) includes red algae, Chlorophyta (C) includes green algae, and Phaeophyta (D) includes brown algae. These choices are incorrect as they do not align with the specific characteristics and classification of diatoms within the kingdom Protista.