Correct Answer: B

Rationale: The correct answer is B: Bacillus subtilis. Bacillus subtilis is known for its ability to resist heat and radiation due to its formation of endospores, which are highly resistant structures that protect the bacterium from harsh environmental conditions. This resilience allows Bacillus subtilis to survive in extreme environments where other bacteria cannot.

Explanation of other choices:
A: Escherichia coli is not known for its exceptional resistance to heat and radiation.
C: Pseudomonas aeruginosa is not particularly resistant to heat and radiation compared to Bacillus subtilis.
D: Clostridium perfringens is not as well-known for its heat and radiation resistance as Bacillus subtilis.

Correct Answer: C

Rationale: The correct answer is C:
To perform serodiagnostics of tuberculosis.

Rationale: The negative reaction to the Mantoux test indicates absence of TB infection. Performing serodiagnostics will further confirm the absence of active infection. This is important to rule out TB before considering vaccination or isolation measures.
Summary:
A: BCG vaccination is not necessary as the boy shows a negative reaction to the Mantoux test.
B: Repeating the test in a month is unnecessary as the initial test already showed a negative reaction.
D: Isolating the boy is not warranted as there is no evidence of active TB infection.

Correct Answer: D

Rationale: The correct answer is D because Mycobacterium tuberculosis is a straight or slightly curved rod with occasional polymorphism. This bacterium does not conform to the characteristics of gram-negative coccus (
A), gram-positive coccus (
B), or gram-negative rod (
C). Mycobacterium tuberculosis is characterized by its unique cell wall composition, which includes high lipid content and mycolic acids, contributing to its acid-fast staining property. The other choices are incorrect because they do not accurately describe the morphology of Mycobacterium tuberculosis.

Correct Answer: A

Rationale: The correct answer is A: Pseudomonas aeruginosa. Pseudomonas aeruginosa is a gram-negative bacilli that produce pyocyanin, a blue-green pigment. The presence of greenish fluorescent colonies of gram-negative nonsporeforming bacilli that release blue-green pigment matches the characteristics of Pseudomonas aeruginosa.

Now, let's analyze the other choices:
B: Enterobacteriaceae - While some Enterobacteriaceae can be gram-negative bacilli, they do not typically produce pyocyanin or exhibit the specific characteristics described in the question.
C: Staphylococcus aureus - Staphylococcus aureus is a gram-positive cocci, not a gram-negative bacilli. It does not match the given description.
D: Staphylococcus epidermidis - Staphylococcus epidermidis is also a gram-positive cocci, not a gram-negative bacilli. It does

Correct Answer: A

Rationale: The correct answer is A: Corynebacterium diphtheriae. This bacterium causes diphtheria, characterized by a grayish pseudomembrane in the throat. The dark blue-staining rods with polar granules seen in microscopic examination are known as metachromatic granules, which are specific to Corynebacterium diphtheriae. Streptococcus pyogenes (choice
B) causes strep throat but does not produce pseudomembranes. Haemophilus influenzae (choice
C) can cause respiratory infections but does not typically present with a pseudomembrane. Neisseria gonorrhoeae (choice
D) is a sexually transmitted bacterium and is not associated with the symptoms described.