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A wound infection culture grew Gram-positive cocci in clusters. The bacteria were catalase-positive and coagulase-negative. What is the likely microorganism?
- A. Staphylococcus epidermidis
- B. Staphylococcus aureus
- C. Streptococcus pyogenes
- D. Enterococcus faecalis
Correct Answer: A
Rationale: The correct answer is A: Staphylococcus epidermidis. The presence of Gram-positive cocci in clusters, along with being catalase-positive and coagulase-negative, is indicative of Staphylococcus species. Staphylococcus epidermidis is commonly found on the skin, making it likely to cause wound infections.
Summary:
B: Staphylococcus aureus is catalase-positive and coagulase-positive.
C: Streptococcus pyogenes is catalase-negative.
D: Enterococcus faecalis is catalase-negative.
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Which of the following bacteria is associated with Lyme disease?
- A. Borrelia burgdorferi
- B. Clostridium botulinum
- C. Escherichia coli
- D. Streptococcus pneumoniae
Correct Answer: A
Rationale: The correct answer is A: Borrelia burgdorferi. This bacterium is associated with Lyme disease, a tick-borne illness. Borrelia burgdorferi is transmitted to humans through the bite of infected black-legged ticks. It causes a range of symptoms, including fever, rash, joint pain, and neurological problems.
Summary:
B: Clostridium botulinum is associated with botulism, a serious illness caused by a toxin produced by this bacterium.
C: Escherichia coli is a common bacterium found in the intestines of humans and animals, some strains can cause food poisoning.
D: Streptococcus pneumoniae is a bacterium that can cause pneumonia and other respiratory infections, but not Lyme disease.
The type of antibody that can cross the placenta is:
- A. IgA
- B. IgM
- C. IgG
- D. IgD
Correct Answer: C
Rationale: The correct answer is C: IgG. IgG is the only antibody that can cross the placenta due to its small size and unique structure, allowing it to provide passive immunity to the fetus. IgA is mainly found in mucosal secretions, IgM is too large to cross the placental barrier, and IgD plays a role in B cell activation but is not involved in placental transfer.
Which of the following is a characteristic feature of Gram-positive bacteria?
- A. Outer membrane
- B. Thin peptidoglycan layer
- C. Thick peptidoglycan layer
- D. Presence of LPS
Correct Answer: C
Rationale: The correct answer is C: Thick peptidoglycan layer. Gram-positive bacteria have a thick peptidoglycan layer in their cell wall, which retains the crystal violet stain during Gram staining. This thick layer is a key characteristic feature that helps differentiate Gram-positive bacteria from Gram-negative bacteria.
Rationale:
1. Gram-positive bacteria retain the crystal violet stain due to their thick peptidoglycan layer.
2. This thick layer provides structural support and protection to the cell.
3. Gram-positive bacteria lack an outer membrane, which is a feature of Gram-negative bacteria (Choice A).
4. Thin peptidoglycan layer is a characteristic of Gram-negative bacteria, not Gram-positive (Choice B).
5. Presence of LPS (lipopolysaccharide) is a feature of Gram-negative bacteria, not Gram-positive (Choice D).
In summary, the presence of a thick peptidoglycan layer is a characteristic feature of Gram-positive
Microscopic analysis of tissue sampling from affected area of mucous membrane of oral cavity revealed bacillus in form of accumulations that looked like a pack of cigarettes. Ziehl-Neelsen staining gives them red colour. What kind of pathogenic organism was most likely revealed in tissue sampling?
- A. M.leprae
- B. M.tuberculosis
- C. A.bovis
- D. A.israilii
Correct Answer: B
Rationale: The correct answer is B: M.tuberculosis. The description of bacillus in the form of accumulations resembling a pack of cigarettes and staining red with Ziehl-Neelsen staining is characteristic of Mycobacterium tuberculosis. M.leprae (Choice A) is associated with leprosy and does not typically appear as described. A.bovis (Choice C) is a type of Mycobacterium but is not typically found in the oral cavity. A.israilii (Choice D) is not associated with the characteristics mentioned in the question. Therefore, based on the specific characteristics described, M.tuberculosis is the most likely pathogenic organism revealed in the tissue sampling.
What is the role of coagulase in bacteria like Staphylococcus aureus?
- A. It facilitates adhesion to surfaces
- B. It breaks down red blood cells
- C. It forms clots to evade immune responses
- D. It aids in antibiotic resistance
Correct Answer: C
Rationale: The correct answer is C because coagulase helps bacteria like Staphylococcus aureus to form clots, allowing them to evade the host immune response. This mechanism helps the bacteria to hide from the immune system and establish infection.
A. Adhesion to surfaces is usually facilitated by other factors like adhesins.
B. Breaking down red blood cells is not a function of coagulase.
D. Antibiotic resistance is typically mediated by other mechanisms like efflux pumps or enzymatic inactivation, not coagulase.