100% Free American Society for Microbiology ABMM Practice Test Questions and Answers 2026

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:

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?

A research laboratory is investigating the mechanisms of viral latency in herpes simplex virus type 1 (HSV1). During latency in sensory neurons, the viral genome exists as a circular episome. Whichof the following viral gene products is thought to play a crucial role in maintaining this latent state and preventing viral gene expression?

A clinical laboratory performs a cefoxitin disk diffusion test on a Staphylococcus aureus isolate from a wound culture. The zone of inhibition measures 18 mm. According to current CLSI M100 guidelines, how should this result be interpreted regarding oxacillin/methicillin susceptibility?

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: