In vitro and in vivo activity of new strains of Bacillus subtilis against ESBL-producing Escherichia coli: an experimental study

Aims The gastro-intestinal tract is a major reservoir of extended-spectrum beta-lactamase (ESBL) producing Escherichia coli. Bacillus spores may be used as probiotics to decrease digestive colonization by ESBL-E. coli. Our aim was to assess the in vitro and in vivo activity of new Bacillus strains against ESBL-E. coli. Methods and Results We screened the in vitro activity of 50 Bacillus strains against clinical isolates of ESBL-E. coli and selected B. subtilis strains CH311 and S3B. Both strains decreased ESBL-E. coli titers by 4 log(10) CFU L-1 in an in vitro model of gut content, whereas the B. subtilis CU1 strain did not. In a murine model of intestinal colonization by ESBL-E. coli, CH311 and S3B did not decrease fecal titers of ESBL-E. coli. Ten sequences of putative antimicrobial peptides were identified in the genomes of CH311 and S3B, but not in CU1. Conclusions Two new B. subtilis strains showed strong in vitro activity against ESBL-E. coli. Significance and Impact of Study Despite strong in vitro activities of new B. subtilis strains against ESBL-E. coli, intestinal colonisation was not altered by curative Bacillus treatment even if their spores proved to germinate in the gut. Thus, this work underlines the importance of in vivo experiments to identify efficient probiotics. The use of potential antimicrobial compounds identified by genome sequencing remains an attractive alternative to explore.

Automated summary

The study found that two new B. subtilis strains showed strong in vitro activity against ESBL-E. coli, significantly reducing their titers in an in vitro model. However, these strains did not decrease the fecal titers of ESBL-E. coli in a murine intestinal colonization model, highlighting the importance of in vivo experiments to evaluate the efficacy of probiotics.