Case Presentation: A 61-year-old male with a past medical history of pancreatic and renal transplants on chronic immunosuppression presented with a six-day history of watery diarrhea. He also reported fever, abdominal pain, and noted a family member also developed a similar diarrhea after a pork dinner. His vital signs were remarkable for fever (101.8 F) and tachypnea (22 bpm). On admission, physical exam was remarkable for abdominal distension and tenderness, without rebound tenderness or guarding. Stool studies were negative for occult blood, Clostridioides toxin, shiga toxin producing Escherichia coli, Salmonella, Shigella, Campylobacter, Aeromonas, and Pleisiomonas. A computed tomography (CT) abdomen demonstrated delayed bowel transit without small bowel obstruction or graft abnormalities. Due to patient’s immunosuppressed state, broad-spectrum antibiotic therapy was initiated with ceftriaxone and doxycycline. On the next day, workup noted positive blood cultures growing Bacillus pumillus. The patient remained febrile (100.8 F), with persistent diarrhea. He was continued on antibiotics with fluid supplementation with symptomatic improvement. Repeat serum cultures were negative three days later, and the patient was discharged on a four day course of levofloxacin.
Discussion: Several species of Bacillus such as B. cereus and B. anthracis are well-known pathogens for gastrointestinal disease. However, little is known about the pathogenicity of Bacillus pumilus. Due to its ubiquitous nature, B. pumilus is a gram-variable rod that is a widely regarded contaminant in clinical microbial studies. However, there have been rare instances of B. pumilus causing active infections, causing symptoms of postprandial epigastric pain and diarrhea, with dizziness, headaches, back pain, and chills that can persist for several days. B. pumilus has also been associated with a case of septic arthritis, cutaneous infections similar to anthrax lesions, central venous catheter infections, and sepsis in newborns and immunocompromised individuals. Non-B. cereus strains, such as B. pumilus, have shown sensitivities to imipenem, vancomycin, and ciprofloxacin. For cutaneous infections, amoxicillin-clavulanate and ciprofloxacin have also shown efficacy. Our patient was originally treated with ceftriaxone and doxycycline with good clinical improvement and was transitioned to levofloxacin at discharge.
Conclusions: Though a common laboratory contaminant, B. pumilus is associated with a variety of infections. Hence, it is essential for hospitalists to use the clinical context of an acute illness in a vulnerable host to detect and treat this infection.