We investigated the kinetics of growth, metabolism and antimicrobial activity of Bifidobacterium thermophilum RBL67 and Pediococcus acidilactici UVA1 previously isolated as a consortium from human baby faeces and producing antimicrobial proteinaceous compounds. Cell growth, antimicrobial activity, glucose consumption, organic acid production and pediocin-gene expression were monitored during pure and mixed strain batch cultures with controlled pH (6.0) at 37 degrees C. The balance of the two strains in mixed cultures was stable, yielding high cell count of 10(9) CFU ml(-1) after a very short incubation time of 4 h for UVA1 and 7 h for RBL67, and RBL67 was not affected by the high production of pediocin by UVA1 during co-culture (up to 12.8 mu g ml(-1)). Furthermore, a real-time PCR assay was developed and allowed gene-expression analysis of the pediocin-gene pedA. The co-culture of RBL67 and UVA1 showed high stability, cell yields and bacteriocin production during batch cultures and has potential for use as a probiotic mixture with antibacterial properties. In addition, a gene-expression real-time PCR assay was successfully developed, used for the relative quantification of the pediocin transcript pedA and demonstrated to be a valuable complementary tool to activity assay. This is the first study reporting of a stable mixed culture of two bacteriocin-producing strains of human origin.