A patient with a history of liver transplantation develops a bloodstream infection with a Gram-negative bacterium. The isolate is identified as Sphingomonas paucimobilis. This opportunistic pathogen is known for its ability to:

• A. Degrade a wide range of environmental pollutants.
• B. Exhibit intrinsic resistance to a broad spectrum of antibiotics.
• C. Produce potent exotoxins that directly damage host tissues.
• D. Form biofilms on indwelling catheters and prosthetic devices.

A patient presents with a pruritic rash consisting of raised, serpiginous tracks on their skin. The patient recently returned from a Caribbean vacation and reported walking barefoot on the beach. The MOST likely causative organism is:

• A. Sarcoptes scabiei
• B. Larvae of Ancylostoma braziliense
• C. Larvae of Strongyloides stercoralis
• D. Pediculus humanus

A clinical microbiology laboratory is performing Gram staining on a sputum sample. After adding the crystal violet stain, a delay in the washing step with decolorizer (alcohol-acetone) would MOST likely result in:

• A. Poor adherence of the stain to Gram-positive bacteria.
• B. Gram-positive bacteria appearing pink.
• C. Increased background staining.
• D. Gram-negative bacteria appearing purple.

An outbreak of gastroenteritis occurs among attendees of a company picnic. Epidemiological investigation points towards contaminated potato salad. Stool cultures from affected individuals grow non-lactose fermenting, Gram-negative rods that are H2S positive on TSI agar. Which pathogen is most likely responsible?

• A. Shigella sonnei
• B. Salmonella Enteritidis
• C. Vibrio cholerae
• D. Enterotoxigenic E. coli (ETEC)