On the fate of ingested Bacillus spores

Spores of various Bacillus species, including B. subtilis, B. cereus and B. clausii, are used as probiotics, although they are generally absent from t he normal microflora of man. We used two nonpathogenic Bacillus species, B. subtilis and B. clausii, to follow the fate of spores inoculated intragast rically in mice. We did not find detectable amounts of vegetative cells in intestinal samples, probably because of high toxicity of the conjugated bil e salt taurodeoxycholic acid against Bacillus species. Both spores and cell s were detected in the lymph nodes and spleen of one mouse. Our results ind icate that Bacillus is present in the intestinal tract solely as spores and that nonpathogenic Bacillus spores may germinate in lymphoid organs, a fin ding reminiscent of B. anthracis germination in macrophages. These results indicate that any claimed probiotic effect of B. subtilis should be due to spores or, alternatively, to vegetative growth outside the intestine. (C) 2 000 Editions scientifiques et medicales Elsevier SAS.