microbiology chapter 11 test bank

Correct Answer: A

Rationale: Rationale for Correct Answer A (Lamblia): 1. Pyriform protozoa with twin nuclei, four pairs of flagella, and a suctorial disc match the characteristics of Giardia lamblia. 2. The presence of two supporting filaments between the nuclei is a unique feature of Giardia lamblia. 3. Giardia lamblia is known to infect the duodenum and cause symptoms such as diarrhea and abdominal pain. Summary of Incorrect Choices: B: Toxoplasma - Toxoplasma gondii is not characterized by four pairs of flagella or supporting filaments in the nuclei. C: Leishmania - Leishmania species do not typically have the described morphology or location in the duodenum. D: Intestinal trichomonad - Intestinal trichomonads do not exhibit the specific features mentioned in the question, such as twin nuclei and supporting filaments.

Correct Answer: C

Rationale: Step-by-step rationale: 1. Shigella is a nonmotile bacterium. 2. This lack of motility is a key characteristic used to differentiate it from other enteric bacteria. 3. Nonmotile nature of Shigella helps it to cause infections by invading the intestinal epithelial cells. 4. Therefore, choice C is correct as Shigella is indeed nonmotile. Summary: A: Incorrect - Shigella does not produce hydrogen sulfide. B: Incorrect - Shigella does not ferment lactose. D: Incorrect - Shigella is not mannitol positive.

Correct Answer: B

Rationale: The correct answer is B: 3.5 to 4.0 billion years. Prokaryotic fossils date back to around 3.5 to 4.0 billion years ago, based on scientific evidence. This timeframe aligns with the earliest known evidence of life on Earth. Choices A, C, and D have incorrect timelines that do not correspond to the established age range of prokaryotic fossils. Choice A is too broad and includes a range that extends beyond the known fossil record. Choices C and D have much younger timelines, which do not match the historical evidence of prokaryotic life dating back billions of years.

Correct Answer: B

Rationale: The correct answer is B: Candida albicans. Candida albicans is the most common cause of vaginal yeast infections due to its ability to overgrow in warm, moist environments like the vagina. It is a type of fungus that naturally resides in the body, but can cause infection when its growth is not regulated. Histoplasma capsulatum (A) causes a lung infection, Aspergillus niger (C) causes fungal sinusitis, and Saccharomyces cerevisiae (D) is a type of yeast used in baking and brewing, not typically associated with vaginal infections.

Correct Answer: A

Rationale: The most likely causative agent is Corynebacterium diphtheriae. Step 1: Presence of rod-shaped bacteria indicates a bacillus. Step 2: Polar granules suggest metachromatic granules seen in C. diphtheriae. Step 3: C. diphtheriae causes diphtheria, which presents with sore throat. Summary: B is incorrect as S. pneumoniae is a cocci, not a bacillus. C is incorrect as H. influenzae is a pleomorphic coccobacillus. D is incorrect as K. pneumoniae is a large, encapsulated bacillus.