Characterization of protease production by a type-III group-BStreptococcus

Abstract

A type-III group-B streptococcus (Streptococcus agalactiae) isolated from a case of late-onset sepsis was examined for protease production. In broth culture, extracellular proteolytic enzymes were not detected until the late exponential phase of growth with maximal protease production occurring during the stationary phase. Three distinct protease pools were isolated from the supernatant fluids of stationary-phase cultures, employing a combination of ion-exchange chromatography and gel-filtration chromatography. One population of proteases (containing two protease pools separable by gel filtration chromatography) eluted from a diethylaminoethyl cellulose column at a sodium chloride gradient concentration of 0.15M while a second population eluted from the same material at a sodium chloride concentration of 0.35M. These protease pools varied in molecular weights from approximately 25,000 daltons to 160,000 daltons as determined by gel filtration on Sephadex G-200. All three protease preparations had pH optima of 8.0–9.0, and all were active against gelatin, human serum albumin, and casein, but were not active against elastin or collagen. In addition, all three protease preparations completely inactivated purified type-III group-B streptococal neuraminidase. The role of these proteases in the disease process caused by the type-III group-B streptococci must remain speculative at this time.