Correct Answer: A

Rationale: The correct answer is A: 4 and 250. Coli index is calculated by dividing the number of red colonies by the volume of water analyzed, which gives 2 red colonies / 500 ml = 4. Coli titer is the reciprocal of the coli index, so it is 1 / 4 = 250. This indicates the concentration of coliform bacteria in the water sample. Choices B, C, and D are incorrect as they do not follow the correct calculation steps for determining the coli index and coli titer. B has the correct coli index but incorrect coli titer. C and D have the values reversed, leading to incorrect results.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus aureus. Staphylococcus aureus is a Gram-positive cocci that is catalase-positive and coagulase-positive, making it the most likely causative agent for the wound infection. Catalase-positive bacteria produce the enzyme catalase, which helps break down hydrogen peroxide. Coagulase-positive bacteria produce the enzyme coagulase, which causes the plasma proteins to clot. Staphylococcus epidermidis is catalase-positive but coagulase-negative, making it less likely to cause a wound infection. Streptococcus pyogenes is catalase-negative, and Enterococcus faecalis is catalase-negative and coagulase-negative, so they are less likely to be the causative agent.

Correct Answer: C

Rationale: The correct answer is C: Gram-negative bacterial outer membrane. Lipopolysaccharides (LPS) are major components of the outer membrane of Gram-negative bacteria. LPS consist of lipid A, core oligosaccharide, and O-antigen. They play a crucial role in the structural integrity and protection of Gram-negative bacteria. Choice A (Gram-positive bacteria) is incorrect because LPS are not present in Gram-positive bacteria. Choice B (Fungal cell walls) is incorrect as LPS are specific to bacterial outer membranes. Choice D (Viral capsids) is incorrect as LPS are not associated with viral structures.

Correct Answer: D

Rationale: The correct answer is D: Loefler. This staining method is used for identifying Corynebacterium diphtheriae, the causative agent of diphtheria. It involves using methylene blue and basic fuchsin to stain the bacteria. The yellow bacilli with blue grains at their ends indicate the characteristic appearance of C. diphtheriae when stained using the Loefler method. Choice A: Ziehl-Nielsen is used for acid-fast bacteria like Mycobacterium tuberculosis. Choice B: Kozlovsky is not a standard staining method in microbiology. Choice C: Romanovsky is used for blood smears to identify malaria parasites.

Correct Answer: D

Rationale: The correct answer is D. Sepsis is a systemic response to infection resulting in organ dysfunction. A: Sepsis can be caused by bacterial infection, but it is not solely defined by the presence of bacteria in the blood. B: Bacteremia is the presence of bacteria in the blood, which can be a component of sepsis, but sepsis involves a broader systemic response beyond just bacteremia. C: Sepsis can lead to the release of toxins and organ failure, but sepsis itself is not defined solely by the massive proliferation of toxins. Therefore, the correct answer is D, as sepsis can involve the presence of bacteria, bacteremia, systemic manifestations, and organ failure.