microbiology chapter 1 test bank

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: B

Rationale: The correct answer is B: Trichomonas vaginalis. Trichomonas vaginalis is a protozoan parasite that can survive and grow in low moisture conditions. It does not require a host cell and can thrive in moist environments, making it able to grow on substances with very low moisture content. Giardia lamblia (A), Balantidium coli (C), and Entamoeba histolytica (D) are all parasites that require a host to survive and reproduce, making them unable to grow on substances with very low moisture content. Trichomonas vaginalis is the only organism among the choices that fits the criteria of being able to grow on low moisture substances.

Correct Answer: C

Rationale: The correct answer is C, Meat-peptone agar, as it provides a simple nutritive media for bacterial growth. This agar contains meat extract and peptone, which are good sources of nutrients for bacterial growth. Glucose broth (A) is a liquid medium with glucose but lacks other essential nutrients. Ascites (serum) agar (B) is a selective medium used for detecting pathogens in clinical samples. Blood agar (D) is a differential medium used to distinguish different types of bacteria based on hemolytic reactions. Meat-peptone agar is the simplest and most general-purpose medium among the options provided.

Correct Answer: C

Rationale: The correct answer is C: Clostridium perfringens. This bacterium is the causative agent of gas gangrene due to its ability to produce gas and toxins in anaerobic conditions. Clostridium tetani causes tetanus, Clostridium botulinum causes botulism, and Bacillus anthracis causes anthrax, not gas gangrene. Clostridium perfringens stands out as the correct choice based on its specific association with gas gangrene and its pathogenic mechanisms.

Correct Answer: D

Rationale: The correct answer is D: stereomicroscopes. These types of microscopes, also known as dissecting microscopes, are designed for observing larger objects like insects or worms. They have a lower magnification power compared to electron microscopes (A), which are used to observe smaller objects at a much higher resolution. Dark-field microscopes (B) are used for observing live and unstained samples with high contrast, not specifically for larger objects. Fluorescence microscopes (C) are used to observe specimens that fluoresce under specific wavelengths of light, not necessarily for large objects like insects or worms. Therefore, the most suitable choice for observing fairly large objects like insects or worms is stereomicroscopes.