Bacteremia Following Alkalihalobacillus clausii (Formerly Bacillus clausii) Administration in Immunosuppressed Adults: A Case Series

(1) Background: Given the widespread use of Alkalihalobacillus clausii (A. clausii) as a probiotic in recent decades and the detection of bacteremia cases in a group of patients, we sought to analyze cases of A. clausii bacteremia following oral probiotic use (2) Methods: A retrospective observational study was conducted at a private hospital in San Jose, Costa Rica. Cases of bacteremia caused by A. clausii confirmed by the microbiology laboratory were analyzed in patients who received oral treatment with this probiotic between January 2020 and January 2022. In addition, an isolate (HCB-AC2) was compared through whole genome sequencing to demonstrate the correlation of bacteremia and A. clausii. Possible vulnerability factors related to the development of this condition were determined. (3) Results: Four cases were identified in this hospital over 2 years. Genomic analysis of isolate HCB-AC2, using two different methods, showed identical results. This indicates that HCB-AC2 is genomically identical to ENTpro and the Enterogermina® reference genome. The median age was 71 years, and all patients had some degree of immunosuppression. All patients met at least three sepsis criteria at the time of bacterial identification. Most patients were treated with vancomycin and levofloxacin. Three of the identified patients died. (4) Conclusion: A. clausii can be used as a probiotic, but caution is advised when used in immunosuppressed and elderly patients. These findings align with those reported in similar case studies.