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: Pseudomonas. Pseudomonas bacteria are known to produce yellow-green pigment and a characteristic odor, specifically in meat-peptone agar. This is due to the production of pyoverdin pigment by Pseudomonas. Other choices like Escherichia, Proteus, Klebsiella, and Azotobacter do not typically produce yellow-green pigment or have a characteristic odor in meat-peptone agar.
Therefore, based on the specific characteristics mentioned in the question, Pseudomonas is the most appropriate choice.

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: D

Rationale: The correct answer is D: PCR. PCR (Polymerase Chain Reaction) is the most suitable method for detecting genitourinary chlamydiosis due to its high sensitivity and specificity in detecting the genetic material of Chlamydia trachomatis. PCR can detect even low levels of the pathogen, providing accurate results.
A: Cultural diagnostic is not as sensitive as PCR and may take longer to produce results.
B: ELISA detects antibodies, which may not be present in early stages of infection, leading to false-negative results.
C: CFT (Complement Fixation Test) is an older method with lower sensitivity compared to PCR for detecting chlamydiosis.

Correct Answer: C

Rationale:
Step 1: Chlorhexidine belongs to the group of biguanides, which are commonly used for disinfecting hands, skin, and mucous membranes.

Step 2: It is known to have broad-spectrum antimicrobial activity against various pathogens.

Step 3: The usage of chlorhexidine in healthcare settings for preoperative skin preparation and surgical hand scrub is well-established.

Step 4: The effectiveness and safety profile of chlorhexidine make it a preferred choice for disinfection purposes.
Summary:
- Option A is incorrect as chlorhexidine is not characterized by strong human toxicity.
- Option B is incorrect as chlorhexidine is not classified as an alcohol and is primarily used for disinfecting hands, skin, and mucous membranes.
- Option D is incorrect as chlorhexidine has a wide range of applications in disinfection, especially in healthcare settings.