microbiology chapter 1 test bank

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. The presence of Gram-positive cocci in pairs indicates a bacterial morphology consistent with Streptococcus pneumoniae, a common cause of pneumonia. This bacterium is known to appear in pairs or short chains on Gram stain. Staphylococcus aureus (B) typically presents as clusters of Gram-positive cocci, Neisseria meningitidis (C) is a Gram-negative diplococcus, and Klebsiella pneumoniae (D) is a Gram-negative rod, making them less likely causative agents in this scenario.

Correct Answer: A

Rationale: The correct answer is A: Balantidiasis. The large ciliated protozoa with a kidney-shaped macronucleus described in the stool sample is consistent with Balantidium coli, the causative agent of balantidiasis. Balantidium coli is the only ciliated protozoan parasite that infects humans and presents with these specific characteristics. Giardiasis (B) is caused by Giardia intestinalis, which is flagellated, not ciliated. Amoebiasis (C) is caused by Entamoeba histolytica, which has an amoeboid shape, not ciliated. Trichomoniasis (D) is caused by Trichomonas vaginalis, which is a flagellated protozoan and does not have a kidney-shaped macronucleus. Hence, the correct diagnosis in this case is Balantidiasis.

Correct Answer: D

Rationale: Step 1: Streptococcus pneumoniae is a common cause of community-acquired pneumonia. Step 2: Mycobacterium tuberculosis can lead to tuberculosis, which can manifest as pulmonary tuberculosis. Step 3: Escherichia coli is not typically associated with causing pneumonia. Step 4: Since Streptococcus pneumoniae and Mycobacterium tuberculosis are linked to pneumonia, and Escherichia coli is not, the correct answer is D - All of the above.

Correct Answer: A

Rationale: The correct answer is A: Giardia lamblia. Giardia is a flagellated protozoa with two nuclei, causing diarrhea. It is commonly found in contaminated water sources. Entamoeba histolytica (B) causes amoebic dysentery with trophozoites in stool. Trichomonas vaginalis (C) causes sexually transmitted infections, not diarrhea. Balantidium coli (D) is a ciliated protozoa causing dysentery with ciliated trophozoites. Therefore, Giardia lamblia is the most likely causative agent in this case.

Correct Answer: B

Rationale: The correct answer is B: Typhoid fever, Brucellosis. Both Typhoid fever and Brucellosis are bacterial infections that can lead to bacteremia, the presence of bacteria in the bloodstream. In Typhoid fever, the causative agent Salmonella typhi can enter the bloodstream, causing bacteremia. Similarly, Brucellosis, caused by Brucella species, can also result in bacteremia. Choice A is incorrect because bacteremia is not typically observed in Diphtheria. Choice C, Cholera, is caused by a toxin-producing bacterium and does not usually lead to bacteremia. Choice D, Dysentery, is a condition characterized by bloody diarrhea and is primarily caused by parasites or bacteria that typically do not lead to bacteremia.