S5569 Beyond Probiotics: Lactobacillus paracasei Infection in a Ruptured Hepatic Cyst Mimicking Malignancy

Introduction: Lactobacilli are gram-positive bacilli that are part of the normal gut microbiota. Although generally considered non-pathogenic and commonly consumed as probiotics, certain strains have been associated with life-threatening infections including bacteremia, intra-abdominal abscesses, infected pancreatic necrosis, and infective endocarditis. Here-in, we present an unusual case of a hepatic cyst complicated by lactobacillus infection. Case Description/Methods: A 61-year-old woman presented with a week of abdominal pain, distension, and shortness of breath. Labs showed leukocytosis (20,900/mm3) and elevated alkaline phosphatase (1032 IU/L). Computed tomography revealed a large cystic liver lesion (17.7 × 17 × 14.7 cm) with adjacent cysts and intrahepatic biliary dilation and MRI suggested a malignant mucinous cystic neoplasm with possible local metastasis. Paracentesis revealed reactive mesothelial cells and inflammation but no malignancy. Due to size, location, and vascular involvement, she was not a surgical candidate and was started on ceftriaxone and metronidazole. Her course was complicated by acute abdomen due to cyst rupture for which she underwent emergent laparotomy and washout, revealing murky peritoneal fluid and a perihepatic hematoma. Cultures grew Lactobacillus paracasei. Following drainage and stabilization, she was discharged on oral amoxicillin-clavulanate to rehabilitation. Discussion: This case highlights an unusual but serious complication of probiotic-associated Lactobacillus paracasei infection leading to hepatic cyst abscess, rupture, and septic shock. Although imaging initially mimicked malignancy, percutaneous biopsy confirmed a benign cyst. The presence of Lactobacillus in peritoneal fluid following cyst rupture suggests possible translocation from the gut or hematogenous seeding of the cyst. While hepatic cysts can become secondarily infected, involvement by Lactobacillus is exceedingly rare. This case underscores the need to consider atypical pathogens in intra-abdominal infections, especially given the increasing use of probiotics and similar supplements and illustrates the potential pathogenicity of organisms traditionally regarded as non-threatening, adding to the limited literature on probiotic-related Lactobacillus infections.