ARPP21 and keratitis: To validate the Rcs system activation of these promoters, they were moved into a contact lens-associated keratitis wild-type (WT) isolate of S. marcescens, strain K904, and isogenic mutants with manipulated Rcs systems that confer high (∆gumB) or no (∆rcsB and ∆gumB ∆rcsB) Rcs activity.