Bacillus clausii-associated bacteremia following probiotic use: A report of two cases and a review of the literature

Bacillus clausii bacteremia is a rare but clinically significant complication associated with probiotic use in hospitalized patients. We report two cases in which a clear temporal relationship was observed between probiotic administration and subsequent isolation of B. clausii from blood cultures. In both patients, identification was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), identifying B. clausii, consistent with the microorganism contained in the administered probiotic. Comprehensive clinical evaluation did not identify an alternative source specifically accounting for the isolation of B. clausii. Although B. clausii bacteremia was microbiologically documented in both cases, its contribution to clinical deterioration and death in the second patient could not be established because of severe concomitant infections and other competing conditions. Both patients had significant comorbidities, recent exposure to broad-spectrum antibiotics, and clinical conditions potentially associated with impaired gastrointestinal barrier integrity, factors that may facilitate bacterial translocation and support the biological plausibility of probiotic-associated bacteremia. Although strain-specific evidence suggests that some probiotics, including B. clausii, may reduce antibiotic-associated diarrhea, these potential benefits should be weighed against the risk of invasive infection in vulnerable patients. These cases highlight the importance of individualized risk-benefit assessment when prescribing probiotics in vulnerable hospitalized patients.