Correct Answer: A

Rationale: The correct answer is A: Staphylococcus aureus. This bacterium is characterized by Gram-positive cocci in clusters, catalase-positive, and coagulase-positive. Staphylococcus aureus is a common pathogen causing wound infections due to its ability to produce toxins and enzymes. Staphylococcus epidermidis (B) is catalase-positive but coagulase-negative, making it less likely to cause infections. Streptococcus pyogenes (C) is catalase-negative and typically causes streptococcal infections, not wound infections. Enterococcus faecalis (D) is catalase-negative and typically associated with urinary tract infections. Thus, Staphylococcus aureus is the most likely causative agent based on the given characteristics.

Correct Answer: D

Rationale: The correct answer is D: Cell cultures. Rotavirus diagnosis involves detecting viral antigens in stool samples using cell cultures. Cell cultures allow for the replication of the virus, facilitating its identification. A: Egg inoculation and B: Sensitive laboratory animals are not commonly used for Rotavirus diagnosis due to ethical concerns and practical limitations. C: Ascoli test is used for detecting specific proteins in serum, not for Rotavirus detection in stool samples. In summary, cell cultures are the most appropriate method for laboratory diagnosis of Rotavirus infection due to their ability to support viral replication and antigen detection.

Correct Answer: A

Rationale: Rationale for Correct Answer A (Lamblia): 1. Pyriform protozoa with twin nuclei, four pairs of flagella, and a suctorial disc match the characteristics of Giardia lamblia. 2. The presence of two supporting filaments between the nuclei is a unique feature of Giardia lamblia. 3. Giardia lamblia is known to infect the duodenum and cause symptoms such as diarrhea and abdominal pain. Summary of Incorrect Choices: B: Toxoplasma - Toxoplasma gondii is not characterized by four pairs of flagella or supporting filaments in the nuclei. C: Leishmania - Leishmania species do not typically have the described morphology or location in the duodenum. D: Intestinal trichomonad - Intestinal trichomonads do not exhibit the specific features mentioned in the question, such as twin nuclei and supporting filaments.

Correct Answer: B

Rationale: The correct answer is B: phase-contrast microscope. This type of microscope is ideal for observing living microorganisms because it enhances the contrast of transparent specimens without the need for staining or fixing, allowing for clear visualization of internal structures and movements. Bright-field microscopes (A) are suitable for observing fixed and stained specimens, not living organisms. Fluorescence microscopes (C) are used to detect specific cellular components tagged with fluorescent markers, not ideal for observing overall morphology. Electron microscopes (D) use electron beams and are best for viewing detailed structures at high magnification, but are not suitable for observing living organisms due to the need for vacuum conditions.

Correct Answer: A

Rationale: The most likely diagnosis is Reiter's syndrome. This is suggested by the presence of joint pain, fever, elevated ESR and CRP levels, and chlamydia infection. Reiter's syndrome is a reactive arthritis triggered by an infection elsewhere in the body, such as chlamydia. The patient's symptoms of joint pain and swelling, along with the positive chlamydia test, support this diagnosis. Rheumatic arthritis (Choice B) is not associated with chlamydia infection, making it less likely. Gout (Choice C) typically presents with elevated uric acid levels, which are normal in this case. Bechterew's disease (Choice D) primarily affects the spine and sacroiliac joints, not the sternoclavicular and knee joints as seen in this patient.