Development of a luciferase-based reporter system to monitor Bifidobacterium breve UCC2003 persistence in mice

Background: Probiotics such as bifidobacteria have been shown to maintain a healthy intestinal microbial balance and help protect against infections. However, despite these benefits, bifidobacteria still remain poorly understood at the biochemical, physiological and especially the genetic level. Herein we describe, for the first time, the development of a non-invasive luciferase-based reporter system for real-time tracking of Bifidobacterium species in vivo. Results: The reporter vector pLuxMC1 is based on the recently described theta-type plasmid pBC1 from B. catenatulatum [ 1] and the luxABCDE operon from pPL2lux [ 2]. Derivatives of pLuxMC1, harbouring a bifidobacterial promoter (pLuxMC2) as well as a synthetically derived promoter (pLuxMC3) [ 3] placed upstream of luxABCDE, were constructed and found to stably replicate in B. breve UCC2003. The subsequent analysis of these strains allowed us to assess the functionality of pLuxMC1 both in vitro and in vivo. Conclusion: Our results demonstrate the potential of pLuxMC1 as a real-time, non-invasive reporter system for Bifidobacterium. It has also allowed us, for the first time, to track the colonisation potential and persistence of this probiotic species in real time. An interesting and significant outcome of the study is the identification of the caecum as a niche environment for B. breve UCC2003 within the mouse gastrointestinal tract (GI) tract.