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: A

Rationale: Rationale: The description matches that of Streptococcus pneumoniae, which appears as gram-positive diplococci with slightly pointed opposite ends. Staphylococcus aureus, Neisseria gonorrhoeae, and Neisseria meningitidis do not match the specific characteristics described in the question. Staphylococcus aureus appears in grape-like clusters, while Neisseria species are typically seen as diplococci but lack the pointed shape described. Therefore, the correct answer is A: Staphylococcus aureus.

Correct Answer: C

Rationale: The correct answer is C: Contaminated wounds. Tetanus is caused by the bacterium Clostridium tetani, which enters the body through breaks in the skin such as wounds or cuts. The bacteria produce a toxin that affects the nervous system, leading to muscle stiffness and spasms. Ingestion of contaminated food (choice A) is not a mode of transmission for tetanus. Inhalation of droplets (choice B) is more relevant for respiratory infections. Direct physical contact (choice D) is not the primary mode of transmission for tetanus as the bacteria need a portal of entry such as a wound to cause infection.

Correct Answer: D

Rationale: The correct answer is D: All of the above. - Streptococcus pneumoniae is a common cause of community-acquired pneumonia. - Mycobacterium tuberculosis can cause pulmonary tuberculosis, which can present as pneumonia-like symptoms. - Pseudomonas aeruginosa is an opportunistic pathogen that can cause pneumonia in immunocompromised individuals. Therefore, all three bacteria can cause pneumonia, making option D the correct choice. Options A, B, and C are incorrect because they each represent a bacterium that can cause pneumonia, so only selecting one of them would not encompass all common causes of pneumonia.

Correct Answer: A

Rationale: The correct answer is A: Selective toxicity. Chemotherapy aims to target cancer cells while minimizing harm to healthy cells, known as selective toxicity. This principle is crucial to effectively treat cancer without causing excessive damage to the patient's body. Accumulation in the macroorganism (B) and causing allergies (C) are not fundamental principles of chemotherapy and can lead to harmful side effects. Therefore, the correct answer is A as it aligns with the core objective of chemotherapy.

Correct Answer: B

Rationale: The correct answer is B: Outer membrane with lipopolysaccharides. Gram-negative bacteria have an outer membrane containing lipopolysaccharides (LPS), which are important in pathogenesis and immune response. This feature is unique to Gram-negative bacteria, distinguishing them from Gram-positive bacteria (choice A). Teichoic acids (choice C) are found in the cell walls of Gram-positive bacteria, not Gram-negative. The statement in choice D, absence of a cell wall, is incorrect as all bacteria have a cell wall, although the composition may vary between Gram-negative and Gram-positive bacteria.

Correct Answer: D

Rationale: The correct answer is D because all three bacteria (Clostridium botulinum, Salmonella enterica, Escherich:ia coli) are known to produce toxins causing foodborne illnesses. Clostridium botulinum produces botulinum toxin, causing botulism. Salmonella enterica produces toxins leading to salmonellosis. Escherichia coli can produce toxins like Shiga toxin causing food poisoning. Choices A, B, and C are incorrect because each bacterium is individually known to produce toxins causing foodborne illnesses, thus the correct answer is D.

Correct Answer: A

Rationale: The correct answer is A: Peritoneum. Normal flora refers to the microorganisms that naturally inhabit the human body without causing harm. The peritoneum is a sterile area, so it does not harbor normal flora. The urethra, vagina, and mouth all have normal flora due to their moist and warm environments, which provide an ideal habitat for microorganisms to thrive. The peritoneum, being a sterile cavity that houses organs like the stomach and intestines, does not have a natural microbial population like the other areas mentioned. Therefore, it does not contain normal flora.

Correct Answer: B

Rationale: The correct answer is B. Bacilli are rod-shaped bacteria, some of which are endospore forming. Cocci are spherical, spirals are spiral-shaped, and vibrios are curved rod-shaped bacteria. Bacilli specifically refer to rod-shaped bacteria, making it the correct answer in this context.