Metallopeptidases produced by group B Streptococcus: Influence of proteolytic inhibitors on growth and on interaction with human cell lineages

Group B Streptococcus (GBS) is a major etiologic agent of neonatal bacterial infections and is the most common cause of sepsis and pneumonia in newborns. Surface and secreted molecules of GBS are often essential virulence factors which are involved in the adherence of the bacteria to host cells or are required to suppress the defense mechanisms of hosts. We analyzed the peptidase profiles of GBS by detection of proteolytic activities on SDS-PAGE containing copolymerized gelatin as substrate. Based on the inhibition by o-phenathroline and EGTA, three distinct peptidases of 220, 200 and 180 kDa were identified in the culture medium, besides one major cell-associated proteolytic activity, a 200-kDa metallopeptidase, suggesting that all were zinc-metallopeptidases. GBS culture supernatants, rich in metallotype peptidases, also cleaved fibronectin, laminin, type IV collagen, fibrinogen and albumin. Cleavage of the host extracellular matrix by GBS may be a relevant factor in the process of bacterial dissemination and/or invasion. Notably, metallopeptidase inhibitors strongly blocked GBS growth as well as its interaction with human cell lineages. Understanding the contribution of peptidases to the pathogenesis of GBS disease may broaden our perception of how this significant pathogen causes severe infections in newborn infants.