Plaa-som is a Thai fermented fish prepared from freshwater fish and various ingredients. In this study, two strains of lactic acid bacteria (LAB) isolated from natural plaa-som fermentation were used as starter cultures: Lactobacillus plantarum IFRPD P15 and Lactobacillus reuteri IFRPD P17. These strains were used as a mixed starter culture for plaa-som using an air-drying method (laminar airflow) with sterilized rice grains as the filler. This method produced a suitable starter culture, which was maintained at 4 degrees C for more than 20 weeks. LAB were the dominant bacteria in the starter culture and produced high acidity from 24 h until the end of fermentation. This resulted in decreased pH in plaa-som. L plantarum IFRPD P15 was dominant as an acidity producer, whereas L rented IFRPD P17 showed an ability to suppress and eliminate pathogenic bacteria such as Escherichia coil within 24 h. The use of a single starter culture for plaa-som resulted in incomplete suppression of pathogenic bacteria and elimination of E. coil. Thus, L plantarum IFRPD P15 and L reuteri IFRPD P17 have great potential for use as a mixed starter culture in plaa-som fermentation and may possibly help to reduce fermentation time. (C) 2010, The Society for Biotechnology, Japan. All rights reserved.