Nokea
In an agar slant, bacterial colonies that appear separate or semiconfluent are referred to as:
- A. filiform
- B. echinulate
- C. beaded
- D. effuse
Correct Answer: C
Rationale: The correct answer is C: beaded. In an agar slant, beaded colonies appear as separate or semiconfluent, forming small, round colonies with gaps between them. This term accurately describes the appearance of the colonies in this context.
A: Filiform colonies are dense and opaque with smooth edges, not separate or semiconfluent.
B: Echinulate colonies have spiny projections, not the characteristic of separate or semiconfluent growth.
D: Effuse colonies spread out extensively and lack defined borders, unlike the distinct appearance of separate or semiconfluent colonies.
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Microscopy of sputum revealed acid-fast bacilli stained red against a blue background using Ziehl-Neelsen staining. What disease does this finding suggest?
- A. Tuberculosis
- B. Diphtheria
- C. Pneumonia
- D. Leprosy
Correct Answer: A
Rationale: The presence of acid-fast bacilli stained red against a blue background indicates mycobacteria, specifically Mycobacterium tuberculosis in this case. Ziehl-Neelsen staining is commonly used to detect tuberculosis. Diphtheria is caused by Corynebacterium diphtheriae, which does not stain with Ziehl-Neelsen. Pneumonia is a general term for lung infections caused by various pathogens. Leprosy is caused by Mycobacterium leprae, which requires special staining methods different from Ziehl-Neelsen.
A patient with suspected liver abscess was admitted to the surgical department. The patient had been staying for a long time on business in one of African countries and fell repeatedly ill with acute gastrointestinal disorders. What protozoal disease may the patient be now ill with?
- A. Amebiasis
- B. Trypanosomosis
- C. Leishmaniasis
- D. Malaria
Correct Answer: A
Rationale: Rationale: The correct answer is Amebiasis (choice A) because the patient's symptoms of acute gastrointestinal disorders and prolonged stay in an African country suggest exposure to Entamoeba histolytica, the causative agent of amebiasis. This protozoal infection commonly occurs in tropical regions, including Africa. Trypanosomosis (choice B) is caused by Trypanosoma species transmitted by tsetse flies, primarily found in sub-Saharan Africa. Leishmaniasis (choice C) is transmitted by sandflies and presents with skin lesions or visceral involvement, not acute gastrointestinal symptoms. Malaria (choice D) is caused by Plasmodium parasites transmitted by mosquitoes and typically presents with fever, not acute gastrointestinal disorders. Therefore, choices B, C, and D are incorrect based on the patient's clinical presentation and travel history.
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.
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.
Which of the following bacteria produce endotoxins?
- A. Streptococcus pneumoniae
- B. Clostridium tetani
- C. Escherichia coli
- D. Staphylococcus aureus
Correct Answer: C
Rationale: The correct answer is C: Escherichia coli. E. coli is a gram-negative bacterium, which means it has an outer membrane containing lipopolysaccharides (LPS), also known as endotoxins. Endotoxins are released when the bacterium is destroyed, causing an inflammatory response.
Streptococcus pneumoniae (choice A) is a gram-positive bacterium and does not produce endotoxins. Clostridium tetani (choice B) produces exotoxins, not endotoxins. Staphylococcus aureus (choice D) is also a gram-positive bacterium and does not produce endotoxins.
In summary, E. coli is the correct answer because it is a gram-negative bacterium that produces endotoxins, while the other choices are gram-positive bacteria that do not produce endotoxins.