microbiology chapter 1 test bank

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.

Correct Answer: A

Rationale: Rationale: 1. Endo agar inhibits the growth of Gram-positive bacteria. 2. Colorless colonies on Endo agar indicate lactose non-fermenting bacteria. 3. Shigella dysenteriae is a lactose non-fermenting, Gram-negative rod, causing dysentery. 4. Salmonella typhi, Escherichia coli, and Proteus vulgaris are lactose fermenters, so they would produce pink colonies on Endo agar. Therefore, the most likely causative agent is Shigella dysenteriae.

Correct Answer: A

Rationale: The correct answer is A: Pertussis bacillus. The symptoms described - elevated temperature and typical cough - are indicative of whooping cough, caused by Bordetella pertussis. By inoculating mucus from the nasopharynx on agar, the doctor is trying to isolate the causative agent, which is likely to be Pertussis bacillus. Summary of other choices: B: Pfeiffer's bacillus (Haemophilus influenzae): Unlikely as symptoms do not match. C: Listeria: Unlikely as it typically causes foodborne illness, not respiratory infections. D: Klebsiella: Unlikely as it is more commonly associated with pneumonia in immunocompromised individuals.

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 because spores are heat-resistant and require high temperatures for destruction. Autoclaving at 121�C for 15-20 minutes ensures spore destruction due to the high pressure and temperature. Choice B (heating to 80�C) is insufficient to destroy spores. Choice C (boiling at 100�C for 10 minutes) is also inadequate as spores require higher temperatures for elimination. Choice D (None of them) is incorrect as autoclaving is the standard method for spore sterilization.