MDS PREP
What is the significance of "Rose spots" in typhoid fever?
1) They indicate the presence of a complication such as intestinal perforation.
2) They are a diagnostic sign of typhoid fever.
3) They indicate the patient is no longer infectious.
4) They indicate the patient has developed antibodies to the bacterium.
General Microbiology Answer: 2The presence of "Rose spots" can
help in diagnosing typhoid fever, as they are relatively specific to this
illness. They typically appear in the trunk and are not a result of increased
sensitivity to the touch or pressure.
Which of the following acids is intermediate in the biosynthesis the cell wall?
1. Alanyl diaminopimelic
2. L-glutamic
3 Uridylic
4. N-acetyl muramic
Microbiology
Answer: 4
N-acetyl muramic is intermediate in the biosynthesis the cell wall
What is the typical pH range for optimal growth of meningococci?
1) 6.8-7.0
2) 7.4-7.6
3) 8.0-8.2
4) 7.0-7.2
The optimal pH range for the growth of meningococci is 7.4-7.6.
Which of the following is a feature of the immune response involving HLA class I antigens?
1) They activate B cells
2) They present antigens to CD4+ T cells
3) They are involved in graft rejection
4) They are only present in the thymus
General Microbiology Answer: 3HLA (Human Leukocyte Antigen) class I antigens are crucial in the immune response to infections and also play a significant role in graft rejection. They present antigens to CD8+ T cells (cytotoxic T cells), which then target and destroy infected or foreign cells. While they do not directly activate B cells or CD4+ T cells, they are involved in the recognition of cells by the adaptive immune system and thus are important in the overall immune response.
Example Test for type IV hypersensitivity:
1) Coagulase test
2) Mantoux test
3) Schick test
4) Elek’s test
Microbiology Answer: 2
A classic example of delayed type IV hypersensitivity is the Mantoux tuberculin test in which skin induration indicates exposure to tuberculosis.
This reaction is called "delayed hypersensitivity" because it is mediated by sensitized CD4+ T lymphocytes which process antigens in association with class II HLA molecules and release lymphokines.
The lymphokines promote a reaction (especially mediated through macrophages) beginning in hours but reaching a peak in 2 to 3 days.
Hypersensitivity reactions with this mode of action include:
Granulomatous diseases (mycobacteria, fungi)
Tuberculin skin reactions
Transplant rejection
Contact dermatitis
Cytotoxic T lymphocyte (CTL) mediated responses: CD8+ T cells are generated and lyse specific cells. Class I HLA molecules play a role. Reactions with this mode include:
Neoplastic cell lysis
Transplant rejection
Virus-infected cell lysis
Which of the following is a characteristic of endotoxins that makes them distinct from exotoxins?
1) They are heat labile
2) They are actively secreted by bacterial cells
3) They are proteins
4) They are part of the bacterial cell wall
General Microbiology Answer: 4
Endotoxins are components of the outer membrane of Gram-negative bacteria and are released when the bacteria die or divide. This structural characteristic differentiates them from exotoxins, which are secreted by living bacteria.
Which of the following is NOT a characteristic of the spore formation in C1. Perfringens?
1) Central or equatorial spores, giving the bacillus a spindle shape
2) Subterminal spores, causing the bacillus to appear club shaped
3) Oval and terminal spores, resembling a tennis racket
4) Spherical and terminal spores, resulting in a drumstick appearance
General Microbiology Answer: 3
C1. Perfringens forms subterminal spores, which cause the bacillus to appear club-shaped under the microscope. The tennis racket appearance is not a characteristic of C1. Perfringens spore formation.
What does the Vi antigen of S. typhi confer upon the bacterium?
1) Resistance to antibiotics
2) Increased invasiveness
3) Resistance to phagocytosis
4) Resistance to acidic environment
General Microbiology Answer: 3the Vi antigen of S. typhi confers upon the bacterium Resistance to phagocytosis. The Vi antigen is a polysaccharide capsule that protects the bacteria from being engulfed and destroyed by phagocytic white blood cells, contributing to its virulence.