A 37-year-old male was admitted to a hospital complaining of abdominal pain, difficulty in swallowing and breathing, constipation, and nausea. He developed respiratory failure and required endotracheal intubation and ventilation. Two days before, the patient consumed dried salted fish bought from an artisanal producer. Laboratory investigation for infectious pathogen was performed using Kitt-Tarozzi's method. Observation under a bright field microscopy revealed the presence of typical microorganisms with tennis racket appearance. Which of the following is the most likely diagnosis?

Correct Answer: A

Rationale: The correct answer is A: Botulism. Botulism is caused by the toxin produced by Clostridium botulinum bacteria found in improperly preserved or canned foods. The symptoms described align with botulism, such as difficulty swallowing and breathing due to muscle paralysis. The tennis racket appearance seen under microscopy corresponds to the characteristic appearance of Clostridium botulinum spores. The other choices can be ruled out based on the clinical presentation and microscopy findings. Cholera typically presents with severe watery diarrhea, Nontyphoidal Salmonella infection with fever and gastrointestinal symptoms, and Typhoid fever with high fever and abdominal pain. Therefore, the most likely diagnosis in this case is botulism.

Correct Answer: A

Rationale: The correct answer is A: Sabouraud's peptone agar. This agar is specifically designed for the isolation of yeast and molds due to its low pH and high sugar content, creating an environment conducive for their growth. Yeast-like fungi thrive in this selective medium, while inhibiting the growth of bacteria and other contaminants. Summary: - Sabouraud's peptone agar is ideal for cultivating yeast-like fungi. - Endo agar is used for isolation of gram-negative bacteria, not fungi. - Milk-salt agar is used for lactobacilli and streptococci, not fungi. - Meat infusion agar is a general-purpose medium for cultivation of a wide range of microorganisms, not specifically for yeast-like fungi.

Correct Answer: A

Rationale: The correct answer is A. Benzylpenicillin sodium salt, also known as penicillin G, works by blocking the synthesis of peptidoglycan in the microbial cell wall. Peptidoglycan is crucial for the structural integrity of bacterial cell walls. By inhibiting its synthesis, penicillin disrupts the cell wall formation, leading to cell lysis and bacterial death. Choices B, C, and D are incorrect because penicillin does not target cytoplasm proteins, thiol enzymes, or RNA synthesis. Penicillin's primary mode of action is specifically related to interfering with bacterial cell wall synthesis.

Correct Answer: B

Rationale: The correct answer is B: cell wall. Lysozyme is an enzyme that targets the cell wall of bacteria by breaking down the peptidoglycan layer, leading to bacterial cell lysis. This action disrupts the structural integrity of the bacteria, ultimately causing their death. Choices A, C, and D are incorrect because lysozyme does not target the cytoplasm, nucleus, or capsule of bacteria. The primary function of lysozyme is to act on the cell wall, making option B the correct answer in this context.

Correct Answer: A

Rationale: The correct answer is A: Giardia lamblia. Giardia lamblia is a protozoan parasite that causes foul-smelling diarrhea. The trophozoites of Giardia lamblia have two nuclei and flagella, which are characteristic features seen on stool microscopy. The presence of these specific features helps differentiate Giardia lamblia from the other options. Entamoeba histolytica (B) typically presents with one nucleus and lacks flagella. Trichomonas vaginalis (C) is a sexually transmitted parasite with a different morphology. Balantidium coli (D) is a ciliated parasite, not flagellated like Giardia lamblia.

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: C

Rationale: The primary target of beta-lactam antibiotics is cell wall synthesis. These antibiotics inhibit enzymes called penicillin-binding proteins, which are essential for building the bacterial cell wall. By disrupting cell wall synthesis, beta-lactam antibiotics weaken the cell wall, leading to bacterial cell lysis and death. Protein synthesis (Choice A), DNA replication (Choice B), and folic acid synthesis (Choice D) are not directly targeted by beta-lactam antibiotics, making them incorrect choices.

Correct Answer: A

Rationale: Rationale for correct answer (A: Escherichia coli): 1. Endo agar selects for Gram-negative bacteria. 2. Red colonies on Endo agar indicate lactose fermentation, characteristic of E. coli. 3. E. coli is a common cause of pneumonia, especially in immunocompromised patients. Summary of why other choices are incorrect: - B: Klebsiella pneumoniae: Typically forms mucoid colonies on agar. - C: Pseudomonas aeruginosa: Produces characteristic greenish-blue colonies on agar. - D: Proteus mirabilis: Does not typically ferment lactose, so would not produce red colonies on Endo agar.

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.