Blastocystis in a Liver Abscess: An Unusual Extraintestinal Location.

Blastocystis is a common anaerobic protist of uncertain pathogenicity that inhabits the human intestine. Rare cases reported in the literature suggest possible extraintestinal dissemination by unclear mechanisms. We followed a 43-year-old Peruvian woman presenting with low-grade fever and gastrointestinal symptoms who was diagnosed with a liver abscess by ultrasound and CT imaging. Identification of the causative agents was achieved through a combination of mass spectrometry, molecular methods (PCR and Sanger sequencing) and culture-based methods in blood, tissue and faecal samples. We detected gut-associated aerobic and anaerobic bacteria, including Escherichia coli, Eikenella corrodens and Bacteroides fragilis. Active forms of Blastocystis subtype ST1 were identified in the liver abscess fluid and successfully cultured in vitro. These findings suggest translocation of gut microbiota into the portal circulation as the underlying route of infection. Blastocystis can act as an opportunistic invasive microorganism in locations other than the intestinal tract.