Evaluation of proteoglycan loss by comparing safranin O (SafO) scores in SPF and germ-free (GF) mice. The SafO staining scores are shown for the DMM operated and unoperated control (CTRL) joints and were reported as either MAX scores (A,B), SUM scores (E,F) for the joint or specifically for medial tibia (MT) (C,D). Panels A,C,E are showing results from mice of all ages and B,D,F from the younger mouse group. Dot plots of the mean ± S.E.M.