Nokea
While examining a blood smear taken form a patient and stained by Romanovsky's method a doctor revealed some protozoa and diagnozed the patient with Chagas disease. What protozoan is the causative agent of this disease?
- A. Trypanosoma cruzi
- B. Toxoplasma gondii
- C. Leishmania donovani
- D. Leishmania tropica
Correct Answer: A
Rationale: Rationale:
1. Chagas disease is caused by Trypanosoma cruzi.
2. Trypanosoma cruzi is transmitted by triatomine bugs.
3. On a blood smear stained with Romanovsky's method, Trypanosoma cruzi appears as trypomastigotes.
4. Toxoplasma gondii causes toxoplasmosis, not Chagas disease.
5. Leishmania donovani and Leishmania tropica cause different forms of leishmaniasis, not Chagas disease.
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Which of the following antibodies is synthesized by the infant soon after birth?
- A. IgA
- B. IgM
- C. IgG
- D. IgD
Correct Answer: B
Rationale: The correct answer is B: IgM. IgM is the first antibody synthesized by the infant soon after birth. It is produced by B cells in response to initial exposure to antigens. IgA is mainly found in mucosal areas, IgG is transferred from mother to fetus, and IgD functions in the early stages of B cell development. Therefore, IgM is the most suitable choice as the antibody synthesized by the infant soon after birth.
A wound culture revealed Gram-positive cocci in clusters. The bacteria were catalase-positive and coagulase-negative. What is the most 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 indicates a staphylococcal species. The fact that the bacteria are catalase-positive and coagulase-negative further narrow it down to Staphylococcus epidermidis, as this species fits all the given characteristics.
- Choice B, Staphylococcus aureus, is coagulase-positive.
- Choice C, Streptococcus pyogenes, is a streptococcal species, not staphylococcal.
- Choice D, Enterococcus faecalis, is a Gram-positive cocci but is catalase-negative and not typically found in clusters.
Which of the following bacteria is responsible for causing the disease known as tuberculosis?
- A. Mycobacterium tuberculosis
- B. Neisseria meningitidis
- C. Salmonella enterica
- D. Streptococcus pneumoniae
Correct Answer: A
Rationale: The correct answer is A: Mycobacterium tuberculosis. This bacteria is responsible for causing tuberculosis because it is the specific pathogen known to infect the lungs and other parts of the body, leading to the disease. Mycobacterium tuberculosis has unique cell wall components that allow it to evade the immune system and survive in the host.
Neisseria meningitidis (B) causes meningitis, not tuberculosis. Salmonella enterica (C) causes food poisoning, not tuberculosis. Streptococcus pneumoniae (D) causes pneumonia, not tuberculosis. Therefore, the correct answer is A based on the specific characteristics and pathogenicity of Mycobacterium tuberculosis.
Microscopic analysis of dental plaque revealed flagellated protozoa without a cyst stage. What microorganism is likely present?
- A. Trichomonas tenax
- B. Entamoeba gingivalis
- C. Balantidium coli
- D. Giardia lamblia
Correct Answer: A
Rationale: The correct answer is A: Trichomonas tenax. Trichomonas tenax is a flagellated protozoan commonly found in the oral cavity and does not have a cyst stage. This organism typically inhabits the gingival crevices and can be identified in dental plaque samples. Entamoeba gingivalis (B) is an amoeba and does not have flagella. Balantidium coli (C) is a ciliated protozoan that infects the intestines, not the oral cavity. Giardia lamblia (D) is a flagellated protozoan that infects the intestines and has a distinct cyst stage. Therefore, the presence of flagellated protozoa without a cyst stage in dental plaque indicates Trichomonas tenax is likely present.
Which of the following media is the most selective for Vibrio cholerae?
- A. MacConkey's agar
- B. Chocolate agar
- C. SS agar
- D. TCBS
Correct Answer: D
Rationale: The correct answer is D: TCBS. Thiosulfate-citrate-bile salts-sucrose (TCBS) agar is the most selective for Vibrio cholerae due to its high salt content, bile salts, and sucrose. Vibrio cholerae can grow well in alkaline conditions, which are provided by TCBS agar. MacConkey's agar (A) is selective for gram-negative bacteria, but not specifically for Vibrio cholerae. Chocolate agar (B) is a non-selective medium suitable for fastidious organisms. SS agar (C) is selective for Salmonella and Shigella species, not Vibrio cholerae.