Which bacterial structure allows for attachment to host cells?

Correct Answer: B

Rationale: The correct answer is B: Fimbriae. Fimbriae are hair-like appendages found on the surface of bacteria that enable attachment to host cells. This attachment is crucial for establishing infection. Flagella (A) are used for movement, not attachment. Capsules (C) provide protection and help evade the host immune system, but do not directly facilitate attachment. Endospores (D) are dormant structures for survival, not for attachment to host cells. Fimbriae specifically aid in adherence to host cells, making them the correct choice in this context.

Correct Answer: B

Rationale: Step-by-step rationale for choice B being correct: 1. The conclusion should be based on evidence or observations. 2. "Doubtful" suggests uncertainty, indicating lack of definitive safety. 3. Choice A is too absolute without considering potential risks. 4. Choice C uses extreme language without proper evidence. 5. Choice D is overly definitive without considering varying levels of contamination. Therefore, choice B is the most reasonable conclusion.

Correct Answer: A

Rationale: The correct answer is A: Amoxicillin. Amoxicillin is commonly used in combination therapy with metronidazole and bismuth compounds like De-Nol to eradicate Helicobacter pylori infection in children. Amoxicillin targets the bacterial cell wall synthesis, working synergistically with metronidazole to effectively eradicate the infection. Tetracycline (choice B) is not recommended in children under 8 years old due to potential tooth discoloration. Oleandomycin (choice C) is not commonly used for H. pylori infection. Biseptol (choice D) is a combination of sulfamethoxazole and trimethoprim, not typically used for H. pylori eradication.

Correct Answer: B

Rationale: The correct answer is B: Staphylococcus aureus. This bacterium is a common causative agent of skin infections like carbuncles. Staphylococcus aureus is known for its ability to produce pus-filled abscesses, which aligns with the symptoms described in the question. The presence of a vesicular rash around the carbuncle further supports this diagnosis, as Staphylococcus aureus can cause skin lesions. The other choices are not correct because: A: Bacillus anthracis causes anthrax, which presents with different symptoms such as fever, malaise, and respiratory symptoms. C: Bacillus subtilis is a harmless soil bacterium commonly used in research and not known to cause skin infections. D: Bacillus anthracoides is not a known pathogen and is not associated with human infections.

Correct Answer: C

Rationale: The correct answer is C: Obligate anaerobes cannot tolerate oxygen. They lack the enzymes needed to detoxify reactive oxygen species generated in the presence of oxygen. This makes them unable to survive in oxygen-rich environments. Choice A is incorrect because obligate anaerobes do not require oxygen to survive. Choice B is incorrect because obligate anaerobes specifically require the absence of oxygen. Choice D is incorrect because obligate anaerobes cannot even tolerate low levels of oxygen.

Correct Answer: A

Rationale: The correct answer is A: Tryptic soy agar is a general-purpose medium suitable for cultivating a wide range of microorganisms. It provides essential nutrients for growth without inhibiting specific types of bacteria. Blood agar (B), Mannitol salt agar (C), and MacConkey agar (D) are selective or differential media designed to promote the growth of specific types of bacteria or differentiate between different bacterial species. Therefore, they are not considered general-purpose mediums.

Correct Answer: C

Rationale: The correct answer is C: Kirby-Bauer disk diffusion test. This test is used to determine the antibiotic susceptibility of bacteria by measuring the zone of inhibition around antibiotic-soaked paper disks. It helps identify which antibiotics are effective against the bacteria being tested. This test is crucial in guiding antibiotic treatment decisions. A: Gram stain is used to classify bacteria based on their cell wall composition and morphology, not for antibiotic susceptibility testing. B: Catalase test is used to differentiate between catalase-positive and catalase-negative bacteria, not for antibiotic susceptibility testing. D: Endospore stain is used to detect the presence of endospores in bacteria, not for antibiotic susceptibility testing.

Correct Answer: A

Rationale: The correct answer is A: nucleic acid and proteins. Viruses consist of genetic material (nucleic acid) surrounded by a protein coat. The nucleic acid carries the viral genetic information, while the proteins form the capsid that protects the genetic material. This combination is essential for the virus to infect host cells and replicate. Lipids (choice B) are not typically part of the main structure of viruses. Lipids are more commonly found in the host cell membrane. Lipids and proteins (choice C) may be present in the viral envelope but are not the main structural components. Proteins and glycoproteins (choice D) are important for viral attachment and entry into host cells but do not constitute the main structural components of viruses.

Correct Answer: A

Rationale: Flagella are the correct answer because they are long, whip-like structures that aid in bacterial movement towards or away from chemical stimuli. They rotate like propellers, allowing the bacterium to navigate its environment. Pili are used for attachment, not movement. Capsules are involved in protection and adherence, not chemotaxis. Fimbriae help in attachment to surfaces, not in movement towards stimuli.