CPB1 and keratitis: As described below, the serine protease Pseudomonas protease IV (PIV), exotoxins exoS, exoU and exoT, P. aeruginosa small protease (PASP), Elastases, and extracellular factors such as lipopolysaccharide (LPS) are bacterial determinants that have an established link to keratitis (Table 1).