A toxicological screen to determine in vitro survival and competition of environmentally applied pseudomonads with mouse fecal microbiota

Abstract

Engineered bacterial strains have been developed for several environmental uses, including bioremediation and application as biopesticides. Previous in vivo work in this laboratory examined the colonization and competition potential of Pseudomonas spp., isolated from a commercial product for PCB degradation with the intestinal flora of CD‐1 mice. In the present study, the same pseudomonads and two additional Escherichia coli strains were evaluated by an in vitro tier testing approach developed to screen environmentally relevant microorganisms for their ability to colonize the mammalian intestinal tract and compete with the normal intestinal tract flora. In the initial tier, the competitor strains were tested for their ability to survive in anaerobic pure culture. Next, they were cultured anaerobically in the presence of mouse fecal microbiota. Finally, serial transfers were performed to monitor the survival and competition potential of each strain with the fecal microbiota. All of the tested strains survived for 48 h in pure culture, and all survived for 24 h in culture with the mouse fecal microbiota. Escherichia coli strains survived serial transfer through five cultures, although in declining numbers. Environmental Pseudomonas spp. survived transfer through three cultures but were not detected after four transfers. No effects of the competitor strains on the fecal microbiota were found. This in vitro system eventually will be used with human fecal microbiota. The potential consequences of human exposure to environmentally released microorganisms can then be extrapolated by comparison of human in vitro results with rodent in vitro and in vivo results in a parallelogram approach.