Monitoring and survival of Lactobacillus paracasei LTH 2579 in food and the human intestinal tract

A PCR-based detection system specific for Lactobacillus paracasei LTH 2579 was developed and applied to follow the fate of the strain in complex ecosystems. This strain was isolated from fruit mash and was characterised as being highly resistant to low pH and bile at concentrations as they occur in the human digestive tract. The application of the subtraction hybridisation technique permitted to identify a 235 bp chromosomal DNA fragment of strain LTH 2579. Based on this target sequence a specific PCR system was developed and combined with the species-specific PCR system for L. paracasei. This combination of PCR based detection systems was successfully applied to monitor L. paracasei LTH 2579 in fermented sausages which were inoculated with this strain (2.0 x 10(7) CFU/g) together with the strongly competitive L. sakei LTH 681 (1.0 x 10(6) CFU/g). At the time of consumption of the sausages the respective counts were 1.8 x 10(7) and 1.4 x 10(8) CFU/g. After consumption of the sausages by three volunteers L. paracasei LTH 2579 was recovered from fecal samples. The counts determined for the strain ranged between 1.2 x 10(7) and 1.5 x 10(8) CFU/g of feces. The fortuitous lactobacilli constituted a share of 5-12% of the lactobacilli in the fecal flora.