Use of PCR primers and probes based on the 23S rRNA and internal transcription spacer (ITS) gene sequence for the detection and enumerization of Lactobacillus acidophilus and Lactobacillus plantarum in feed supplements.

Novel polymerase chain reaction (PCR) primers designed from the 16S-23S internal transcription spacer (ITS) rRNA and 23S rRNA genes, respectively, were used for the specific detection of Lactobacillus acidophilus and Lactobacillus plantarum. Molecular weights of the PCR products were 221 and 599 bp, respectively. Strains of L. acidophilus and L. plantarum obtained from the culture center, dairy products, infant stool and other samples, could be identified with these PCR primers. DNAs from other lactic acid bacteria (LAB) species including strains of Lactobacillus pentosus which was closely related to L. plantarum, and bacteria species other than LAB, would not generate the false positive results. When this PCR primer set was used for the detection of L. acidophilus and L. plantarum in feed supplement or feed starter samples, reliable results were obtained. Furthermore, when these L. acidophilus or L. plantarum specific primers were used as DNA probes for the colony hybridization of L. acidophilus and L. plantarum, the viable cells of these LAB species in culture and feed supplements or starter products could be identified and enumerized. The method described here thus offers a rapid and economic way to inspect and assure the quality of the feed supplements or fermentation starters.