Medical examination of the first-year pupils included Mantoux test. 15 pupils out of 35 had negative reaction. What actions should be taken against children with negative reaction?

Correct Answer: A

Rationale: The correct answer is A: BCG vaccination. The Mantoux test is used to detect tuberculosis infection. A negative reaction means the child is not infected. BCG vaccination is recommended for individuals without prior TB infection to prevent severe forms of the disease. Antitoxin and rabies vaccinations are not related to TB and are not indicated in this scenario. Repeating the Mantoux test is unnecessary since a negative result indicates absence of TB infection.

Correct Answer: B

Rationale: The correct answer is B: pertussis toxin. This toxin is the most important virulence factor of Bordetella pertussis because it plays a key role in causing the characteristic symptoms of whooping cough. Pertussis toxin interferes with the host's immune response, leading to inflammation and tissue damage in the respiratory tract. The other choices (A: the flagellum, C: P fimbriae, D: mannose-resistant adhesins) are important for bacterial attachment and colonization, but they do not directly contribute to the severity of the disease like pertussis toxin does.

Correct Answer: B

Rationale: Rationale: 1. Streptococcus pyogenes is the causative agent of strep throat. 2. If untreated, strep throat can lead to rheumatic fever. 3. Rheumatic fever is an autoimmune complication of streptococcal infections. 4. E. coli, S. epidermidis, and S. aureus are not typically associated with rheumatic fever.

Correct Answer: B

Rationale: The correct answer is B: Vibrio cholerae. Vibrio cholerae is a comma-shaped rod bacterium that causes high volume watery diarrhea by producing cholera toxin. This toxin leads to the secretion of large amounts of fluid into the intestines. Campylobacter jejuni (A) typically causes bloody diarrhea. Pseudomonas aeruginosa (C) and Proteus mirabilis (D) are not associated with high volume watery diarrhea.

Correct Answer: B

Rationale: The correct answer is B because Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis are the most common causative agents of bacterial meningitis. Haemophilus influenzae is often seen in children, Streptococcus pneumoniae is the most common in adults, and Neisseria meningitidis is common in adolescents and young adults. Choice A is incorrect because although Streptococcus group B and Listeria monocytogenes can cause meningitis, E. Coli K1 is not a common causative agent. Choice C is incorrect because Staphylococcus aureus and Pseudomonas aeruginosa are not typically associated with bacterial meningitis. Choice D is incorrect as there are known causative agents for bacterial meningitis.

Correct Answer: C

Rationale: The correct answer is C: cell wall composition. Gram staining differentiates bacteria based on the structure of their cell walls. It classifies bacteria into Gram-positive (thick peptidoglycan layer) and Gram-negative (thin peptidoglycan layer). This differentiation is crucial for identifying bacterial species and guiding treatment choices. Size and shape (choice A) are not specific to Gram staining. Presence of flagella (choice B) is related to bacterial motility, not Gram staining. Genetic material (choice D) is not directly assessed by Gram staining. Overall, the unique composition of the cell wall is the key factor in distinguishing bacteria through Gram staining.

Correct Answer: A

Rationale: The correct answer is A: Shigella dysenteriae. This bacterium produces Shiga toxin, which inhibits protein synthesis by inactivating the ribosomes. Shigella dysenteriae is known to cause severe gastrointestinal infections. Choice B: Escherichia coli typically does not produce toxins that inhibit protein synthesis. E. coli strains may produce toxins that cause diarrhea. Choice C: Clostridium tetani produces tetanospasmin toxin, which affects the nervous system but does not inhibit protein synthesis. Choice D: Staphylococcus aureus produces toxins like enterotoxins and exotoxins but these toxins do not directly inhibit protein synthesis.

Correct Answer: C

Rationale: The correct answer is C: Identification. Bacteria are studied by identification to determine their specific characteristics and differentiate between different species. Taxonomy (A) is the science of classification, not specific to bacteria. Classification (B) is the process of grouping organisms based on shared characteristics, not specific to bacteria. Nomenclature (D) is the naming system for organisms, not the primary method for studying bacteria. Therefore, identification (C) is the correct choice for studying bacteria.

Correct Answer: A

Rationale: Step 1: Gram-negative rod with safety pin appearance indicates bipolar staining. Step 2: Yersinia pestis is a Gram-negative rod causing bubonic plague. Step 3: Y. pestis has bipolar staining due to its unique F1 capsule. Step 4: The swollen lymph node and bacteremia are consistent with bubonic plague. Step 5: Therefore, the correct answer is A: Yersinia pestis. Summary: - B: Clostridium tetani causes tetanus, not characterized by a safety pin appearance. - C: Brucella melitensis causes brucellosis, not characterized by a safety pin appearance. - D: Pasteurella multocida causes animal bites infections, not characterized by a safety pin appearance.