Lactic acid bacteria isolated from boza, a cereal-fermented beverage from Belogratchik, Bulgaria, were screened for the production of bacteriocins. Thirteen of the 52 strains isolated inhibited the growth of Pediococcus spp., Listeria innocua and Lactobacillus plantarum. One of the strains, identified as Pediococcus pentosaceus ST18, produced pediocin ST18 at 3200 arbitrary units (AU) ml(-1) in MRS broth at the end of logarithmic growth (i.e. after 24h). Concentration by ammonium sulfate precipitation, followed by separation in a Sep-Pack C-18 column and reverse-phase HPLC on a C18 Nucleosil column yielded two active antimicrobial peptides, which suggests that pediocin ST18 may be a two-peptide bacteriocin. The peptide had bacteriostatic action towards L. innocua, with no cell lyses. Pediocin ST18 remained active after 30 min at 121degreesC and after 2 h of incubation at pH 2-12. No loss in activity was recorded after treatment with alpha-amylase, SDS, Tween 20, Tween 80, urea, Triton X-100, N-laurylsarcosin, EDTA and PMSF. Pediocin ST18 does not adhere to the cell surface of the producer strain. (C) 2004 Elsevier Ltd. All rights reserved.