We investigated the effects of lactic acid bacterial (LAB) cells in rats using fluorescence in situ hybridization (FISH) targeting 16S rRNA to identify the cecal microbial community. We designed a novel species-specific 16S rDNA probe to detect Lactobacillus rhamnosus (Lrham454). Subtractive technique using the LAC722 probe (Sakai et al. 2004 Journal of Bioscience and Bioengineering 98, 48) under different hybridization stringency (LAC722(L-H)) was applied to identify Lactococcus lactis. We also applied Lplan447 and LAC722(L) to detect Lactobacillus plantarum and a wide range of LAB (total LAB), respectively. We optimized the hybridization and washing conditions and then quantified L. rhamnosus, L. plantarum, and L. lactis cells in rat cecal contents. We monitored increases in individual bacterial populations and in total LAB caused by the administration of the corresponding LAB cells. Growth, food efficiency and internal disorders did not significantly differ among the rats administered with LABs. Rats administered with polydextrose (POL) developed diarrhea, which decreased the total numbers of cecal bacteria, whereas the simultaneous administration of POL and L. rhamnosus KY-3 eased this symptom, and recovered the numbers of total LAB and of L. rhamnosus.
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