microbiology chapter 11 test bank

Correct Answer: A

Rationale: Step-by-step rationale: 1. Clostridium botulinum is known for producing the neurotoxin causing botulism. 2. Botulinum toxin paralyzes muscles, leading to symptoms of botulism. 3. Clostridium tetani produces tetanus toxin causing muscle rigidity, not botulism. 4. Streptococcus pneumoniae causes pneumonia, not botulism. 5. Escherichia coli can cause food poisoning, but not botulism. Summary: Choice A is correct (Clostridium botulinum) due to its association with botulism and neurotoxin production. Choices B, C, and D are incorrect as they are associated with different diseases and toxins.

Correct Answer: A

Rationale: The correct answer is A: Entamoeba histolytica. This is because it is the only choice that matches the description of cysts with four nuclei, characteristic of Entamoeba histolytica. Entamoeba histolytica is a protozoan parasite that causes amoebiasis, leading to symptoms like persistent diarrhea. The other choices can be eliminated for the following reasons: B: Balantidium coli - It is a ciliated protozoan that causes dysentery in humans but does not produce cysts with four nuclei. C: Giardia lamblia - It is a flagellated protozoan that causes giardiasis, but it forms cysts with only two nuclei. D: Trichomonas hominis - It is a flagellated protozoan found in the human intestine, but it does not produce cysts with four nuclei. Therefore, based on the description of cysts with four nuclei in the stool sample,

Correct Answer: B

Rationale: The correct answer is B: phase-contrast microscope. This type of microscope is ideal for observing living microorganisms because it enhances the contrast of transparent specimens without the need for staining or fixing, allowing for clear visualization of internal structures and movements. Bright-field microscopes (A) are suitable for observing fixed and stained specimens, not living organisms. Fluorescence microscopes (C) are used to detect specific cellular components tagged with fluorescent markers, not ideal for observing overall morphology. Electron microscopes (D) use electron beams and are best for viewing detailed structures at high magnification, but are not suitable for observing living organisms due to the need for vacuum conditions.

Correct Answer: A

Rationale: The correct answer is A: Tuberculin. The Mantoux test involves injecting tuberculin, a protein derivative of Mycobacterium tuberculosis, under the skin to check for a delayed hypersensitivity reaction in individuals exposed to TB. B: BCG vaccine is a live attenuated vaccine used for TB prevention, not for diagnostic testing. C: DTP vaccine is for diphtheria, tetanus, and pertussis, not TB. D: Tularinum is not a standard immunobiological preparation used for TB testing. Therefore, A is the correct choice for the Mantoux test.

Correct Answer: D

Rationale: The correct answer is D: Middlebrook's medium. This medium is specifically designed for the growth of Mycobacterium tuberculosis due to its low concentration of malachite green, which inhibits the growth of other bacteria but not Mycobacterium species. Middlebrook's medium also contains various nutrients that support the growth of Mycobacterium tuberculosis. A: Middlebrook's medium is the correct answer, not incorrect. B: Heart infusion broth is a general-purpose medium, not specific for Mycobacterium tuberculosis. C: MacConkey agar is selective for gram-negative bacteria and would not support the growth of Mycobacterium tuberculosis. In summary, Middlebrook's medium is the ideal choice for cultivating Mycobacterium tuberculosis due to its specific formulation that promotes the growth of this pathogen while inhibiting other bacteria.