Utilisation of doubly stable isotope labelled lactobacillus Johnsonii in humans

Doubly labelled [¹³C,¹⁵N] Lactobacillus johnsonii (dlLa1) was prepared for oral administration in humans.

The aim of the study was to investigate the digestion of dlLa1, the ¹³CO₂-exhalation, the urinary and faecal ¹³C-and ¹⁵N-excretion rates in correlation to orocaecal transit time (OCTT) and the enrichment of blood plasma fractions.

Procedure methods: Ten healthy adults aged 23–36 y received 87mg/kg wet vital dlLa1 cells and 10g raffinose together with a continental breakfast. Expired air samples were taken over 14h, whereas urine and faeces were collected over 2 days. A blood sample was taken 2h after dlLa1 administration. ¹³C- and ¹⁵N-enrichments were measured by isotope ratio mass spectrometry (SerCon, Crewe, UK), H₂-concentations were measured by using an electrochemical detector (Stimotron, Wendelstein, Germany).

Results: Mean OCTT deriving from raffinose ingestion was reached after 3.7h. After dlLa1 administration, 8.6% of ¹³C was exhaled as ¹³CO₂. The resulting mean urinary excretion of ¹³C and ¹⁵N was 1.3 and 12.4%, respectively, whereas the faecal excretion was 39.9 and 37.6%, respectively. Two h after dlLa1 administration, ¹³C- and ¹⁵N-enrichment of fibrinogen amounted to 0.007 and 0.009 at%exc, respectively.

Conclusions: In comparison to OCTT of 3.7h, both stable isotopes appear after 30min in breath and urine, clearly indicating that dlLa1 is rapidly digested in the small bowel before reaching the caecum. This is confirmed by ¹³C-and ¹⁵N-enrichments of blood plasma fractions. The ingestion of dlLa1 in healthy adults led to a total excretion of approximately 50% of both stable isotopes. However, as to what extent the remaining half of La1 is still viable enough to re-colonise the colon remains open.