Which organism is an intracellular parasite of red blood cells and can be cultured from blood in the acute stage?

• A. Burkholderia mallei
• B. Haemophilus aegyptius
• C. Bartonella bacilliformis
• D. Yersinia pestis

Answer: (C)

Bartonella bacilliformis is known for invading and multiplying inside red blood cells, a situation that leads to acute bacteremia during Oroya fever. Because the organism can be present within erythrocytes in the blood during the acute stage, it can be recovered from blood cultures, though it grows slowly and often requires specialized, enriched media and extended incubation. This intracellular red blood cell parasitism distinguishes it from the other options: Burkholderia mallei tends to infect tissues and macrophages rather than RBCs; Haemophilus aegyptius is a conjunctival pathogen that needs specific growth factors and does not inhabit red blood cells; Yersinia pestis is associated with plague and does not characteristically reside inside red blood cells. Thus, Bartonella bacilliformis best fits the description.