The trouble in tracing opportunistic pathogens: cholangitis due to Bacillus in a French Hospital caused by a strain related to an Italian probiotic?

Two published unrelated case reports, one in France and one in Italy, describe infections due to Bacillus subtilis strains resistant to erythromycin and penicillin. While the Italian isolate was correlated to a national probiotic, the French strain differed from the probiotic available in France. 16S rRNA sequencing of the two clinical isolates and the respective probiotics revealed 100% identity of both clinical isolates to the Italian probiotic and classified the strains as Bacillus clausii, while the French probiotic was found to be Bacillus thuringiensis. The present report raises the difficulty of confirming strain identities and thus causal links between probiotic or alimentary microorganisms and strains isolated from immuno-suppressed hosts.