Characterization of L. reuteri DSM 17938.

Two plasmids (= independent DNA fragments in bacteria) carrying the antibiotic resistance genes tet(W) for tetracycline and lnu(A) for lincosamide were removed from the Lactobacillus reuteri strain ATCC 55730 by methods that do not genetically modify the organism’s chromosome. The resulting daughter strain was designated L. reuteri DSM 17938. Direct comparison of the parent and daughter strains for a series of in vitro properties and in a human clinical trial were subsequently performed to assess the retention of probiotic properties in the daughter strain. The clinical trial aimed to study gastrointestinal passage and safety, and included 16 healthy adult subjects. They were randomly assigned to ingest a placebo (n=4), an ATCC 55730 dose of 8x10⁸ CFU/day (n=3), a DSM 17938 dose of 8x10⁸ CFU/day (n=4) or a DSM 17938 high dose of 6.5x10¹⁰ CFU/day (n=5), for 28 days. Faecal samples were collected at baseline, on days 7, 14 and 28 and on days 42 and 56. L. reuteri specific clones were picked and analyzed for genetic content to identify them as L. reuteri ATCC 55730-like or the L. reuteri DSM 17938 strain. Fasting blood samples were collected at baseline and after 28 days. They were analyzed for the levels of major blood components, liver, kidney and immune functions, and major metabolic parameters. On day 28 a general bacterial analysis of the blood was also done, to detect the possible transfer of any bacteria into the blood. General health examinations revealed no changes in weight, pulse, blood pressure or body temperature in any group during the supplementation period. Blood safety and metabolic parameters were also unchanged in all groups. Blood samples taken directly after supplementation on day 28 were negative for bacteraemia.

Conclusions: Removal of two plasmids from the L. reuteri ATCC 55730 strain resulted in a daughter strain designated L. reuteri DSM 17938. Strain comparisons by vitro tests and the clinical trial confirmed that DSM 17938 has retained the probiotic properties of ATCC 55730, is well tolerated and safe to ingest in doses up to 6.5 x 10¹⁰ CFU/day. L. reuteri DSM 17938 survives passage through the human GI tract to the same extent as ATCC 55730. After the 2-week washout period there was no detection of any L. reuteri strain in the supplemented individuals.

Reference

Removal of antibiotic resistance plasmids from Lactobacillus reuteri ATCC 55730 and characterization of the resulting daughter strain L. reuteri DSM 17938. Rosander A, Connolly E, Roos S. (2008) Appl Environ Microbiol. 74:6032-6040.