Bacterial Strains
The Lactobacillus strains used were originally isolated from
healthy human individuals, and kindly provided by Stefan Roos
and Hans Johansson of the Swedish Agricultural University of
Science. Lactobacillus rhamnosus (Kx 151 A1) originated from a
human gastric biopsy. Lactobacillus reuteri (FJ1) originated from
human saliva. Lactobacillus crispatus (MV24-1a) originated from a
human vagina. As described in a previously published study, these
strains adhere to ME-180 cells [11]. The lactobacilli were cultured
with no agitation in liquid MRS broth (Oxoid, Cambridge, UK) or
on Rogosa agar plates (Oxoid, Cambridge, UK) at 37uC. None of
the lactobacillus strains produced detectable levels of hydrogen
peroxide. Overnight cultures of lactobacilli in liquid MRS broth
were collected by centrifugation and washed once in DMEM prior
to the assays that were performed in this study. The optical density
at 600 nm of each bacterial sample was measured to calculate the
number of bacteria that were present per milliliter. For the assays,
the lactobacilli were added to cells in DMEM/10% FBS and
incubated at 37uC in 5% CO2.