HTRA1 and infection: We have previously reported that mutants, in which the entire htrA gene or its serine protease active site had been inactivated, colonize the colon as well as WT bacteria.39,40 Whereas mice infected with WT or pepP complemented bacteria were suffering from severe symptoms including wasting and bloody diarrhea within 1 week post-infection, the induced disease was much less pronounced upon pepP gene deletion, as indicated by lower median clinical scores.