The lactic acid bacteria are an inhomogeneous group which includes among others the genera Pediococcus, Enterococcus, Lactococcus, Lactobacillus and Streptococcus. Among the Pediococcus group, P. acidilactici and P. pentosaceus are widely used for fermentation of food products like vegetable and meat products. By production of organic acids, resulting in pH decrease, they contribute to control the microbial succession during fermentation. They also act as protective cultures preventing the growth of food-borne pathogens such as Listeria monocytogenes or Staphylococcus aureus [1] and by doing this, they extend storage life and enhance safety of food products [2,3]. Beside production of classical antimicrobial compounds such as organic acids or hydrogen peroxide, the protective effect also results from the production of bacteriocins [4]. Bacteriocins are ribosomally synthesized, small, heat-stable antimicrobial peptides produced by bacteria. Pediocin AcH/PA-1 is the most studied class IIa bacteriocin (non modified, nonlantibiotic peptides) and has potential for use as food preservative, due to its strong antilisterial activity [5]. Since amino-acid sequence determination of the pediocin AcH/PA-1 in 1992 [6,7], several pediocin-producing P. acidilactici and P. pentosaceus strains have been screened from a large variety of plants and fruits [8], but also from the gastrointestinal tract of poultry, ducks and other animals [9-11]. Millette et al. [12] recently isolated a strain of Pediococcus acidilactici from human faeces which produces an unidentified antimicrobial proteinaceous compound. To our knowledge, no pediocin-producing Pediococcus has been isolated so far from human faeces and it is therefore unknown to which extent these strains are widespread in the human intestinal microbiota and contribute to the microbial balance of the complex gut ecosystem.
Real-time PCR is a very sensitive and rapid molecular method for the detection of specific genes in complex samples. It is particularly suitable for measuring non cultivable bacteria, because detection is independent of growth conditions of the target organism [13]. It has for example recently been used successfully on faecal samples to assess the survival of Lactococcus lactis subsp. cremoris FC after transit through the gastrointestinal tract [14] or to detect the presence of noroviruses in clinical stool samples [15].
In this work, we report the identification of a new bacteriocin-producing strain of Pediococcus acidilactici (UVA1), which was co-isolated from baby faeces with the bacteriocinogenic strain Bifidobacterium thermophilum RBL67 [16]. The biochemical and genetic characterization of the antimicrobial compound was performed. The distribution of pedA-containing strains in human faeces was also investigated using a newly designed real-time PCR assay targeting the pediocin structural gene.
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