Centrifugation, the pellets were washed three times, centrifuged, and resuspended in 200 l of buffer containing a 1 mM concentration of the substrate. After 60 min, the samples were centrifuged, and the absorbance of the supernatants was measured at 405 nm in an enzyme-linked immunosorbent assay (ELISA) reader. Control values (bacteria incubated in buffer) were used as a blank. No endogenous prote