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A clinical microbiology laboratory is investigating a cluster of Clostridium difficile infections in a hospital. Which of the following methods is MOST appropriate for determining if the isolates from different patients are related?

A clinical trial is evaluating the efficacy of a new antifungal agent against invasive aspergillosis. Serum galactomannan levels are being used as a biomarker to monitor the infection. A decrease in galactomannan levels during treatment would indicate: 

A clinical microbiology laboratory is using flow cytometry to analyze lymphocyte subsets in a patient with suspected immunodeficiency. Which of the following cell surface markers is typically used to identify helper T cells?

During the investigation of a foodborne illness outbreak linked to raw sprouts, several bacterial isolates are obtained from patient stool samples and the implicated food source. Which of the following molecular methods would be MOST useful for establishing a definitive link between the clinical isolates and the food isolate?

A patient develops a severe diarrheal illness after consuming raw seafood. Stool culture yields a Gramnegative, comma-shaped bacterium that is oxidase-positive and grows on thiosulfate-citrate-bile salts-sucrose (TCBS) agar, producing blue-green colonies. The MOST significant virulence factor contributing to the severe, cholera-like diarrhea caused by this organism is: