Which of the following bacteria are capable of producing an exotoxin that causes severe diarrhea?

Correct Answer: D

Rationale: The correct answer is D because all three bacteria mentioned (Clostridium botulinum, Vibrio cholerae, and Escherichia coli) are capable of producing exotoxins that cause severe diarrhea. Clostridium botulinum produces botulinum toxin leading to botulism, Vibrio cholerae produces cholera toxin causing cholera, and some strains of Escherichia coli produce enterotoxins causing severe diarrhea. Choices A, B, and C alone are incorrect because each of them can produce exotoxins that cause severe diarrhea.

Correct Answer: A

Rationale: The correct answer is A: Ziehl-Neelsen staining method was applied. 1. Ziehl's solution is used as a primary stain in Ziehl-Neelsen staining for acid-fast organisms like Mycobacterium tuberculosis. 2. Sulfuric acid is used as a decolorizer to remove excess stain. 3. Methylene blue is not part of the Ziehl-Neelsen staining method. 4. Burri's, Gram's, and Peshkov's staining methods are not used for acid-fast staining.

Correct Answer: D

Rationale: The correct answer is D: Lamblia. The cysts described match the characteristics of Giardia lamblia, a protozoan parasite. Giardia cysts are oval-shaped, 50-60 microns in diameter, and contain 2 nuclei (macronucleus and micronucleus). Giardia is commonly found in contaminated water sources and can cause gastrointestinal illness in humans. Incorrect choices: A: Toxoplasma - Toxoplasma gondii is a parasite that causes toxoplasmosis, transmitted through ingestion of contaminated food or water, but its cysts do not match the description given in the question. B: Amoeba - Amoebas are single-celled organisms, but they do not typically form cysts with visible nuclei as described. C: Balantidium - Balantidium coli is a ciliated protozoan that can cause dysentery in humans, but its cysts do not

Correct Answer: D

Rationale: The correct answer is D: Positive strand RNA viruses. These viruses have RNA genomes that can be directly translated by host ribosomes without the need for transcription. In contrast, single-strand DNA and double-strand DNA viruses require transcription to generate mRNA for translation. Choice A is incorrect as there is a correct answer. Choice B and C are incorrect because both single-strand DNA and double-strand DNA viruses require transcription for mRNA synthesis.

Correct Answer: B

Rationale: The correct answer is B: Outer membrane with lipopolysaccharides. Gram-negative bacteria have an outer membrane that contains lipopolysaccharides, which play a role in pathogenicity and resistance to certain antibiotics. This outer membrane is a distinguishing feature of Gram-negative bacteria, as opposed to Gram-positive bacteria that have a thick peptidoglycan layer. Choices A, C, and D are incorrect because Gram-negative bacteria have a thin peptidoglycan layer, do have a cell wall (although it is different from Gram-positive bacteria), and do not contain teichoic acids.

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.

Correct Answer: A

Rationale: The correct answer is A: Neisseria meningitidis. This is because Neisseria meningitidis is a Gram-negative diplococcus that is oxidase-positive and fermentative. Neisseria gonorrhoeae is also a Gram-negative diplococcus, but it is not fermentative. Moraxella catarrhalis is oxidase-positive but not fermentative. Haemophilus influenzae is Gram-negative but is not a diplococcus, and it is not fermentative. Therefore, based on the characteristics provided in the question, Neisseria meningitidis is the most likely causative agent.

Correct Answer: C

Rationale: Step-by-step rationale: 1. The Filoviridae family includes Marburg virus and Ebola virus. 2. Both viruses are characterized by filamentous, enveloped structure. 3. They cause severe hemorrhagic fever in humans. 4. Lassa virus and lymphocytic choriomeningitis viruses belong to Arenaviridae. 5. Chikungunya virus and Sindbis virus are alphaviruses. 6. Crimean-Congo virus and Hantaan virus are bunyaviruses. 7. Therefore, the correct answer is C.

Correct Answer: B

Rationale: The correct answer is B: protomeres. Viral capsomeres are the building blocks of viral capsids, which are protein coats that enclose and protect the viral genetic material. These capsomeres are made up of smaller subunits called protomeres. Envelopes (A) refer to a lipid membrane surrounding some viruses, not the subunits of capsomeres. Capsids (C) are the protein coats that capsomeres make up, not the subunits themselves. Nucleoids (D) are found in bacterial cells and refer to the region where the genetic material is located, not the subunits of viral capsomeres.