A 32-year-old patient presents after a hiking trip with a circular rash, low-grade fever; blood culture is flagged and Gram stain shows very thin, faint corkscrew-shaped spirochetes. ELISA and Western blot have been performed. Which organism is suspected?

Prepare for the CAMLPR Microbiology Test. Utilize flashcards and engaging multiple-choice questions, each equipped with descriptions and explanations. Ready yourself for an excellent performance!

Recognize Lyme disease by the combination of a thin, corkscrew-shaped spirochete and the classic circular rash after a tick exposure. Borrelia burgdorferi is a spirochete transmitted by Ixodes ticks, and erythema migrans—the round, expanding rash—is a hallmark of early Lyme disease. The observed very thin, faint corkscrew-like organisms fit Borrelia, whose slender morphology makes them hard to see on a routine Gram stain, so special impressions or dark-field/stain techniques are often needed, while serology is used for confirmation.

ELISA screening followed by a Western blot is the standard testing sequence for Lyme disease, because early serology may be negative and become positive as antibodies develop. Among the other organisms listed, each aligns with different diseases or exposure patterns that don’t match this presentation: Leptospira relates to leptospirosis from contaminated water with different clinical features; Treponema pallidum causes syphilis with distinct staging and rash patterns; Bartonella henselae is known for cat-scratch disease with lymphadenopathy rather than a circular tick-associated rash. The combination here most strongly supports Borrelia burgdorferi.