A patient develops a severe diarrheal illness after consuming raw seafood. Stool culture yields a Gram-negative, 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:
What is considered the "gold standard" for routine monitoring of the lethality of steam sterilization (autoclave) cycles in healthcare facilities?
A clinical microbiology laboratory is performing antimicrobial susceptibility testing on a Klebsiella pneumoniae isolate. The isolate is resistant to multiple beta-lactam antibiotics, and further testing reveals the presence of a carbapenemase enzyme. The MOST clinically significant carbapenemase in Klebsiella pneumoniae is often:
A fungal isolate grown from a blood culture at 37°C shows budding yeast cells. When subcultured to cornmeal agar with Tween 80 and incubated at 25°C, it produces pseudohyphae and terminal chlamydospores. Growth on CHROMagar Candida yields green colonies. This organism is most likely:
A clinical microbiology laboratory is implementing a new multiplex nucleic acid amplification test (NAAT) for the detection of respiratory viral pathogens. To ensure the quantitative accuracy of the assay, it is essential to include:
An immunocompromised patient develops a disseminated fungal infection. Blood cultures are consistently negative. However, a serum beta-D-glucan assay is markedly elevated. Tissue biopsy reveals the presence of hyaline, septate hyphae with dichotomous branching. The MOST likely causative organism is:
A clinical microbiology laboratory is performing antimicrobial susceptibility testing using the broth microdilution method. The minimum bactericidal concentration (MBC) is determined by:
A patient develops a localized skin infection after being bitten by a tick. The infection is characterized by a slowly expanding erythematous rash with central clearing (erythema migrans). The MOST likely causative agent is:
A research laboratory is investigating the mechanisms of antigenic variation in Trypanosoma brucei, the causative agent of African trypanosomiasis. The parasite evades the host immune response by periodically changing its surface coat protein. This process primarily involves:
A Gram-positive rod is isolated from the blood culture of a neonate with sepsis. The organism exhibits weak beta-hemolysis on sheep blood agar, is catalase-positive, hydrolyzes esculin in the presence of bile, and demonstrates characteristic "tumbling" motility in a wet mount prepared from a broth culture incubated at 25°C. Which organism is most likely?
