The influence of the probiotic bacterial strain, Bacillus cereus var. toyoi, on the development of total anaerobic growth, enterobacteria, lactic acid bacteria, and Enterococcus spp. associated with intestinal mucosal tissues of piglets before and shortly after weaning was evaluated. Bacterial growth capacities were determined in microtiter plates by incubating mucosal tissue extracts in selective liquid media for enterobacteria, lactic acid bacteria (LAB), Enterococcus spp. or total anaerobic growth. Growth of mucosa-associated enterobacteria was reduced (P<0.05) in samples from the trial group before weaning. Furthermore, growth was similar in all samples, while growth of enterobacteria from the control group increased the closer the samples were taken from the large intestine. Total anaerobic bacteria showed similar development as enterobacteria. Decreased growth was recorded in samples from the small intestine of piglets from the control group at the time of weaning at 28 d of age. Growth of Enterococcus spp. and LAB decreased from d 13 of age and displayed a sharp increase after weaning, independent of probiotic supplementation. It is concluded that B. cereus var. toyoi depressed growth of enterobacteria in the intestinal tract. There are strong indications that the early uptake of already modified microbial populations from faeces of the sow aids in the establishment of similar microbial populations in the piglet.