Preservation by lyophilization of a human intestinal microbiota: influence of the cultivation pH on the drying outcome and re-establishment ability.

Faecal microbiota transplantation is an emerging medical concept for the treatment of gastrointestinal diseases. This concept, however, has disadvantages as low storability of stool and intensive donor screening. A solution to overcome these problems would be the preservation of an in vitro microbiota through freeze-drying. However, the influence of the entire preservation process, including cultivation and lyophilization, has not been assessed so far. In this study, the influences of the process steps cultivation, drying and re-cultivation were determined with cell count, production of metabolites, microbial composition and diversity in the system as evaluation criteria. All pH conditions resulted in stable, culturable communities after re-cultivation. Cell count, richness, diversity and microbial composition were affected by freeze-drying, but these effects were reversible and vanished during re-cultivation. Hence, the re-cultivated system did not differ from the system before drying. The metabolism, measured by short-chain fatty acids as indicators, showed slight changes due to natural dynamics. Consequently, the cultivation prior to drying was identified to have more influence than the drying itself on the preservation process and therefore the biggest potential for optimization. Hence, the highest similarity with the initial stool sample was obtained with pH 6.0 - 6.5 during cultivation.