The present invention relates generally to medicine. More specifically the invention relates to the use of synergistic probiotic bacteria as intervention for health. In particular, the present invention provides a strain of Faecalibacterium prausnitzii and a bacterial strain which has one or more of the characteristics of: (i) being acetate producing, (ii) being lactate consuming and (iii) having the ability to be an electron acceptor, for use in the treatment or prevention of a disease associated with reduced butyrate levels or a disease associated with reduced or low numbers of Faecalibacterium prausnitzii bacteria.