NOS2 and clostridium difficile infection: To determine whether host inducible nitric oxide synthase (iNOS) or arginase responds to CDI, we infected conventional mice with a standard antibiotic pretreatment (1 mg clindamycin per mouse by gavage) and subsequently infected with WT Cd. Compared to uninfected antibiotic-treated controls, mice infected with WT Cd suffered significantly higher tissue damage and inflammatory cell infiltrates quantified by blinded histopathological scoring (Fig. 4a).