DESIGN AND EVALUATION OF A LACTOBACILLUS GROUP-SPECIFIC RIBOSOMAL-RNA-TARGETED HYBRIDIZATION PROBE AND ITS APPLICATION TO THE STUDY OF INTESTINAL MICROECOLOGY IN PIGS

The potential importance of anaerobic bacteria belonging to the Lactob acillus group has been well documented. Appropriate methods to rapidly evaluate species diversity and fluctuations in their population level s within the Lactobacillus group are being developed. Molecular tools such as hybridization probes based on rRNA sequences are well suited t o these studies. The work reported here was undertaken to test the spe cificity of an hybridization probe to specifically recognize microorga nisms of the Lactobacillus group and assess its usefulness as a quanti tative tool to study fluctuations of the Lactobacillus population rela tive to the total bacterial population in gastrointestinal contents of pigs. We have designed a 25-mer oligonucleotide that targets a region common to and specific for the Lactobacillus group 16S rRNA sequences within the available database. The optimal wash temperature of the pr obe was experimentally determined to be 54 degrees C. The results obta ined using the Lactobacillus group-specific probe (LGP) shows thar Lac tobacillus populations vary along the different segments of the gastro intestinal tract (GIT). In weaning piglets, the relative Lactobacillus signal intensity obtained constituted 100% of the relative RNA index in the stomach contents as determined by a bacterial domain probe (BDP ), and between 90 to 100% in the duodenum. The signal of the Lactobaci llus population decreased and reached its minimum in the distal part o f the GIT The same trend was observed in adult pigs, but in the stomac h they constituted no more than 30% as determined by the BDP: and were present at lower levels in the other parts of the GIT. These studies document the quantitative importance of the lactobacilli in the stomac h and small intestine of pigs. Further studies to investigate the role of lactobacilli in promoting the ecological balance of gut bacteria f or probiotic therapy are being undertaken.