Which of the following bacteria is responsible for causing the disease known as tuberculosis?

Correct Answer: A

Rationale: The correct answer is A: Mycobacterium tuberculosis. This bacteria is responsible for causing tuberculosis because it is the specific pathogen known to infect the lungs and other parts of the body, leading to the disease. Mycobacterium tuberculosis has unique cell wall components that allow it to evade the immune system and survive in the host. Neisseria meningitidis (B) causes meningitis, not tuberculosis. Salmonella enterica (C) causes food poisoning, not tuberculosis. Streptococcus pneumoniae (D) causes pneumonia, not tuberculosis. Therefore, the correct answer is A based on the specific characteristics and pathogenicity of Mycobacterium tuberculosis.

Correct Answer: B

Rationale: The correct answer is B: CMV. Patients after allogeneic stem cell transplantation are monitored for CMV reactivation due to its potential to cause severe complications in immunocompromised individuals. CMV can lead to organ damage and even mortality in these patients. Monitoring for CMV reactivation allows for early detection and prompt intervention. Incorrect Choices: A: HAV - Hepatitis A virus reactivation is not commonly monitored in post-transplant patients. C: Rubella virus - Rubella is not a common concern for reactivation in this patient population. D: Measles virus - Measles reactivation is not typically monitored in these patients.

Correct Answer: C

Rationale: Chitin is a polysaccharide found in the cell walls of fungi. Bacteria have cell walls made of peptidoglycan, not chitin. Viruses do not have cell walls as they are acellular entities. Therefore, the correct answer is A: fungi.

Correct Answer: C

Rationale: The correct answer is C: Protection against harsh conditions. Bacterial endospores are dormant structures produced by certain bacteria as a survival strategy under unfavorable conditions. They protect the bacterial DNA and other essential components from damage caused by heat, chemicals, desiccation, and radiation. Endospores do not directly participate in energy production (A), DNA replication (B), or protein synthesis (D). These functions are carried out by the active, vegetative form of the bacterial cell.

Correct Answer: A

Rationale: The correct answer is A: ethylene oxide. Ethylene oxide is a toxic, odorless gas commonly used as a sterilizing agent in healthcare settings due to its ability to effectively kill bacteria, viruses, and fungi. It is a highly reactive compound that can penetrate porous materials, making it an ideal choice for sterilization purposes. Incorrect choices: B: Carbon dioxide is not used as a sterilizing agent and is not toxic. C: Carbon monoxide is not commonly used for sterilization and has a distinct odor. D: Propane is not used for sterilization in healthcare settings and is not odorless.

Correct Answer: B

Rationale: The correct answer is B: Cannot induce infectious disease. Saprophytes are microorganisms that obtain nutrients from decaying organic matter and do not cause infectious diseases in humans. They play a vital role in the ecosystem by decomposing dead organisms. Choice A is incorrect because saprophytes do not cause typical infections. Choice C is incorrect because saprophytes do not cause chronic infections. Choice D is incorrect because saprophytes do not cause mixed infections involving multiple pathogens. Therefore, the correct answer is B as saprophytes do not induce infectious diseases.

Correct Answer: D

Rationale: The correct answer is D: complex. Bacteriophages are considered complex viruses because they have a complex structure consisting of a polyhedral head, a helical tail, and tail fibers. The head contains the viral genetic material, while the tail facilitates attachment to the host bacterial cell. This complexity distinguishes bacteriophages from simpler viruses like helical and icosahedral viruses. Helical viruses have a rod-like shape, while icosahedral viruses have a symmetrical, 20-sided structure. Enveloped viruses have a lipid bilayer envelope surrounding their capsid, which bacteriophages lack. Therefore, the unique and intricate structure of bacteriophages classifies them as complex viruses.

Correct Answer: B

Rationale: The correct answer is B, Streptococcus pneumoniae. This bacterium is the classic causative agent of croupous pneumonia due to its ability to infect the lungs and cause inflammation. Streptococcus pneumoniae is a common pathogen known for causing pneumonia in both adults and children. It is characterized by the presence of a capsule that helps it evade the host immune system. Choice A, Chlamydia pneumoniae, is not the correct answer as it is more commonly associated with atypical pneumonia. Choice C, Mycoplasma pneumoniae, is also associated with atypical pneumonia and not croupous pneumonia. Choice D, Staphylococcus aureus, can cause pneumonia, but it is not the classic causative agent of croupous pneumonia.

Correct Answer: A

Rationale: The correct answer is A: Acid resistance. Tuberculous bacilli are acid-fast bacilli, meaning they resist decolorization by acid-alcohol after staining with Ziehl-Neelsen stain. This property is due to the high lipid content in the cell wall of Mycobacterium tuberculosis. Alkali resistance (B) and alcohol resistance (C) are not specific properties of tuberculous bacilli. Capsule formation (D) is a characteristic of some bacteria but is not a defining feature of tuberculous bacilli.