Which of the following is a key feature of Mycobacterium tuberculosis?

Correct Answer: C

Rationale: The correct answer is C: Acid-fast cell wall. Mycobacterium tuberculosis is characterized by its unique cell wall composition, containing high levels of mycolic acids which make it acid-fast. This property allows it to resist decolorization during acid-fast staining procedures. This distinguishes it from other bacteria. A: Producing spores is not a key feature of Mycobacterium tuberculosis. Spore formation is more commonly associated with bacterial species such as Bacillus and Clostridium. B: Mycobacterium tuberculosis is not Gram-negative. It is classified as acid-fast Gram-positive. D: Mycobacterium tuberculosis does not produce toxins as a key feature. Its pathogenicity is more closely related to its ability to evade host immune responses and persist in host tissues.

Correct Answer: D

Rationale: The correct answer is D because antigens can be composed of lipids, proteins, or polysaccharides. Antigens are molecules that can elicit an immune response in the body. They can be diverse in their chemical composition, leading to the recognition and response by the immune system. Therefore, the correct choice is D as antigens can be any of these chemical components. Choices A, B, and C are incorrect because they each represent a possible chemical composition of antigens, but the flexibility of antigens to be made up of any of these components makes D the most accurate choice.

Correct Answer: A

Rationale: The correct answer is A: Yersinia pestis. Y. pestis is responsible for causing the plague, a severe infectious disease. This bacterium is transmitted via fleas from rodents to humans. It causes bubonic, septicemic, and pneumonic plague. Clostridium difficile causes gastrointestinal infections, Neisseria gonorrhoeae causes gonorrhea, and Pseudomonas aeruginosa can cause various infections but not the plague.

Correct Answer: B

Rationale: The correct answer is B: Uptake of naked DNA from the environment. Bacterial transformation is a process where bacteria take up free DNA from their surroundings and incorporate it into their own genome. This process is essential for genetic recombination and the acquisition of new traits. Plasmids are small DNA molecules that can be transferred between bacteria, but not necessarily through pili. Bacteriophages are viruses that infect bacteria and transfer their DNA, but this is not the primary mechanism of bacterial transformation. Binary fission is a method of bacterial reproduction, not related to the uptake of DNA.

Correct Answer: C

Rationale: Rationale: Choice C is correct because Staphylococcus epidermidis, Escherichia coli, and Enterococcus spp. are common causative agents of nosocomial infections due to their presence on the skin, in the gut, and in healthcare settings. S. aureus and L. monocytogenes (Choice A) are also important pathogens but are less common in nosocomial infections. Enterobacteriaceae (Choice B) are a large family of bacteria that can cause infections but are not as commonly associated with nosocomial infections compared to the organisms in Choice C. The correct answer (Choice C) encompasses pathogens commonly found in healthcare settings, making it the most suitable option.

Correct Answer: B

Rationale: The correct answer is B: Jenner. Edward Jenner performed the first vaccination against smallpox in 1796 by using cowpox virus to immunize individuals. He observed that milkmaids who had contracted cowpox did not get smallpox, leading to the development of the smallpox vaccine. Pasteur is known for germ theory, Semmelweis for handwashing in healthcare, and Koch for identifying the causative agents of diseases. However, none of them performed the first smallpox vaccination like Jenner.

Correct Answer: B

Rationale: The correct answer is B: BKV. BK virus can cause hemorrhagic cystitis in immunocompromised patients by infecting the urinary tract. It primarily affects the renal tubular epithelial cells, leading to hemorrhagic cystitis. EBV (A) causes infectious mononucleosis, HSV1 (C) causes oral and genital herpes, and JCV (D) causes progressive multifocal leukoencephalopathy, none of which are associated with hemorrhagic cystitis.

Correct Answer: B

Rationale: The correct answer is B: Clostridium perfringens. This bacterium is associated with myonecrosis/gas gangrene and can produce enterotoxin causing food intoxication. Clostridium septicum (A) is associated with wound infections but not known for food intoxications. Clostridium histolyticum (C) is not typically associated with myonecrosis or food intoxications. Clostridium novyi (D) is known for causing black disease in sheep and cattle, not food intoxications.

Correct Answer: B

Rationale: The correct answer is B: glycocalyx. The glycocalyx is a matrix formed outside the plasma membrane that consists of glycoproteins and glycolipids. It plays crucial roles in cell-cell recognition, protection, and immune response. Cytoplasm (A) is the gel-like substance inside the cell, not outside. Exoplasm (C) is not a recognized term in biology. Cell wall (D) is a rigid structure found in plant cells, not outside the plasma membrane in all cells.