Comparison of LPS content of mouse pelleted diets. The concentration of LPS was measured to determine the load of microbiota-derived components in mouse diets. The pellets were ground, sonicated in non-pyrogenic water and filtered. LPS concentration in the filtrate was analyzed using the Chromogenic Limulus Amebocyte Lysate (LAL) Test (Cambrex, USA) and is expressed as endotoxin units (EU) per 1 μg of a diet. Results represent the mean (± SE) of four measurements.