A patient with a sore throat and fever had a throat culture revealing Gram-positive cocci in pairs with a capsule. What is the most likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is a Gram-positive cocci that often appear in pairs and can have a capsule. It is a common cause of sore throat and fever, known as streptococcal pharyngitis. Staphylococcus aureus (B) is a Gram-positive cocci but does not typically form pairs. Neisseria meningitidis (C) is a Gram-negative diplococcus and is more associated with meningitis. Klebsiella pneumoniae (D) is a Gram-negative rod and not typically associated with sore throat and fever.

Correct Answer: C

Rationale: The correct answer is C: Reaction type GRUBER. Agglutination reaction in GRUBER involves the clumping of particles due to specific antibodies binding to antigens on the surface. This reaction is commonly used in blood typing and serology tests. A: Western blot is a technique used to detect specific proteins in a sample, not related to agglutination. B: ELISA is an enzyme-linked immunosorbent assay used to detect antibodies or antigens, not based on agglutination. D: Ascoli ring test is a method to detect the presence of DNA in a sample, not related to agglutination.

Correct Answer: C

Rationale: The correct answer is C: E + S = P. This notation represents the interaction between an enzyme (E) and a substrate (S) resulting in a product (P). Enzymes facilitate chemical reactions by binding to substrates and converting them into products. Choice A is incorrect because it does not include the enzyme in the reaction. Choice B is incorrect as it involves two substrates binding to the enzyme, not a substrate converting to a product. Choice D is incorrect as it shows two substrates reacting to form a product without involvement of an enzyme. Thus, choice C accurately represents the process of enzymatic reactions involving enzymes, substrates, and products.

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.

Correct Answer: B

Rationale: The correct answer is B because in immune reactions, a large lattice is formed when antigens and antibodies are in optimal proportion. This optimal ratio allows for the formation of a strong antigen-antibody complex, leading to the aggregation of immune complexes into large lattice structures. When antibodies are in excess (choice A), there may not be enough antigens to form a stable lattice. Similarly, when antigens are in excess (choice C), there may be insufficient antibodies to form a strong lattice. Choice D is incorrect because the optimal proportion of antigens and antibodies is crucial for the formation of large lattices in immune reactions.

Correct Answer: A

Rationale: The correct answer is A: Commensalism. In this relationship, the skin microflora benefits from the host without causing harm or benefitting it. This is evident in the mutualistic interaction where the microflora receive nutrients and a place to live, while the host remains unaffected. Choice B, Infection, is incorrect because it implies harm to the host. Choice C, Parasitism, is also incorrect as it involves one organism benefiting at the expense of the other. Choice D, No correct answer, is not applicable here as Commensalism accurately describes the relationship between the macroorganism and skin microflora.

Correct Answer: A

Rationale: The correct answer is A: Burri-Gins. This staining method specifically targets the detection of capsules in bacteria. It involves staining the capsules with crystal violet and the background with safranin. This staining technique helps visualize the capsules as a distinct halo around the bacteria. Summary: - Choice B (Ziehl-Neelsen) is used for acid-fast staining to detect Mycobacterium species. - Choice C (Neisser) is used for staining Neisseria species. - Choice D (Gram) is a common staining method used to differentiate bacteria based on cell wall composition (Gram-positive and Gram-negative), but it does not specifically target capsules.

Correct Answer: A

Rationale: Rationale: Shigella dysenteriae produces Shiga toxin, which inhibits protein synthesis by inactivating the 60S ribosomal subunit. This disrupts the translation process, leading to cell death. Escherichia coli (choice B) does not produce a toxin that inhibits protein synthesis. Clostridium tetani (choice C) produces tetanospasmin, which affects the nervous system. Staphylococcus aureus (choice D) produces toxins that cause food poisoning but do not inhibit protein synthesis.

Correct Answer: A

Rationale: The correct answer is A: Tetanus. Tetanus is caused by the bacterium Clostridium tetani, commonly found in soil, dust, and animal feces. The patient's history of a stab wound increases the risk of tetanus infection as the bacterium can enter the body through the wound. Tetanus infection can lead to symptoms such as lockjaw or trismus, which are characterized by muscle stiffness and difficulty opening the mouth. This is due to the neurotoxin produced by Clostridium tetani affecting the muscles. Summary of incorrect choices: B: Brucellosis is a bacterial infection transmitted from animals to humans through consumption of unpasteurized dairy products. It does not typically manifest with symptoms of lockjaw. C: Whooping cough (Pertussis) is a respiratory infection caused by Bordetella pertussis bacteria. It presents with severe coughing fits but does not cause lockjaw. D: Anaerobic wound infection