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

Correct Answer: A

Rationale: Step 1: Bordetella pertussis is the causative agent of whooping cough, also known as pertussis. Step 2: This bacterium produces toxins that damage the respiratory tract, leading to severe coughing fits. Step 3: Clostridium tetani causes tetanus, Haemophilus influenzae causes respiratory infections, and Staphylococcus aureus causes skin infections. Step 4: Therefore, A is the correct answer as it is the only bacterium directly associated with whooping cough.

Correct Answer: C

Rationale: The correct answer is C: Staphylococcus aureus. This bacterium is commonly associated with hospital-acquired infections due to its ability to cause a wide range of infections and its resistance to multiple antibiotics. Staphylococcus aureus can cause skin infections, pneumonia, bloodstream infections, and surgical site infections, making it a significant threat in healthcare settings. Escherichia coli (choice A) is more commonly associated with foodborne illnesses. Clostridium difficile (choice B) is known for causing antibiotic-associated diarrhea. Bacillus anthracis (choice D) is primarily associated with anthrax infections, which are not typically acquired in hospital settings.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus saprophyticus. This bacterium is the second most common cause of cystitis in healthy sexually active women after E. coli. Staphylococcus saprophyticus is commonly found in the gastrointestinal and genital areas. It has a unique ability to adhere to uroepithelial cells, making it a common pathogen in urinary tract infections. Proteus mirabilis is more commonly associated with complicated UTIs, especially in catheterized patients. Pseudomonas aeruginosa is more commonly seen in hospitalized or immunocompromised patients. Klebsiella pneumoniae is typically associated with UTIs in elderly patients or those with structural abnormalities in the urinary tract.

Correct Answer: A

Rationale: The presence of acid-fast bacilli stained red using the Ziehl-Neelsen method indicates a mycobacterial infection. Among the choices, tuberculosis is the most common mycobacterial infection affecting the lungs, presenting with acid-fast bacilli in sputum. Leprosy is caused by Mycobacterium leprae, but it typically does not show up in sputum smears. Diphtheria is caused by Corynebacterium diphtheriae, which is not acid-fast. Pneumonia is a general term for lung inflammation caused by various pathogens, not specifically mycobacteria. Therefore, the correct diagnosis is tuberculosis based on the microscopy findings.

Correct Answer: D

Rationale: The correct answer is D (All of the above) because all three bacteria (Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus) are known to cause urinary tract infections. E. coli is the most common causative agent of UTIs due to its ability to colonize the urethra. P. aeruginosa can cause UTIs in hospitalized patients with catheters. S. aureus is less common but can lead to UTIs, especially in individuals with underlying health conditions. Therefore, all three bacteria are potential pathogens for UTIs. Choices A, B, and C are incorrect because each of these bacteria can individually cause UTIs, making the correct answer D.

Correct Answer: C

Rationale: The correct answer is C: flagella. Flagella are whip-like structures that move fluid, mucus, or cells over the surface of a cell. They are longer and fewer in number compared to cilia, which are shorter and more numerous. Fimbriae are small, bristle-like structures that help bacteria attach to surfaces but do not move fluid. Microvilli are tiny projections that increase the surface area for absorption but do not have a role in moving fluid or cells. Therefore, flagella is the correct answer as it specifically fits the function described in the question.

Correct Answer: B

Rationale: The correct answer is B because the complement fixation test is a serological test that detects the presence of specific antibodies or antigens in a patient's serum. It works by measuring the ability of antibodies to fix complement proteins. Choice A is incorrect because the complement fixation test typically involves several steps, not necessarily three. Choice C is incorrect as standardized complement proteins are commonly used in this test. Choice D is incorrect because sheep red blood cells are not essential for performing the complement fixation test.

Correct Answer: D

Rationale: The correct answer is D because the flu vaccine primarily stimulates systemic immunity rather than local immunity. It is administered parenterally (C) as it is injected into the body. It is a subunit vaccine (B) as it contains only specific antigens of the virus. It is a recommended vaccine (A) due to its effectiveness in preventing influenza. In summary, D is the correct choice as the flu vaccine mainly targets systemic immunity, not local immunity, unlike the other characteristics listed.

Correct Answer: A

Rationale: The correct answer is A: Vibrio cholerae. This is because Vibrio cholerae is a Gram-negative, comma-shaped bacterium known to cause cholera. The characteristic shape and the association with cholera make it the most likely causative agent in this case. Explanation for incorrect choices: B: Shigella dysenteriae - Shigella dysenteriae is a Gram-negative bacterium that causes bacillary dysentery, not cholera. C: Salmonella typhi - Salmonella typhi is a Gram-negative bacterium that causes typhoid fever, not cholera. D: Campylobacter jejuni - Campylobacter jejuni is a Gram-negative bacterium that commonly causes foodborne gastroenteritis, not cholera.