M-like proteins of Streptococcus dysgalactiae

Streptococcus dysgalactiae is one of the most important bacterial species i solated from bovine mastitis. To identify potential virulence factors of th is species we prepared chromosomal DNA from strain 8215 and constructed a p hage display library, By affinity selection of the library against fibrinog en (Fg), we isolated and characterized a gene, called demA, encoding a prot ein with the molecular mass of similar to 58 kDa, called DemA, displaying b oth plasma protein binding properties and sequence similarities with the M and M-like proteins of other streptococcal species, Purified recombinant De mA protein was found to completely inhibit Fg-binding to cells of S. dysgal actiae. A continued sequence analysis revealed that the demA gene was prece ded by an open reading frame (dmgA) coding for a putative protein, called D mgA, with high similarities to the Mga proteins of Streptococcus pyogenes, By additional cloning, the corresponding dmgA and demA genes from another s train, called Epi9, were isolated and analyzed. These genes, called dmgB an d demB, respectively, revealed a high degree of similarity to the correspon ding genes in strain 8215. Increased binding of Fg by cells of strain Epi9, grown in an atmosphere with 10% CO2, was correlated to an enhanced transcr iption of the demB gene as shown in a Northern blot. Strain 8215 did not re spond to CO2, which could be explained by a nonfunctional dmgA gene due to insertion of an insertion sequence element, Based on sequence similarities of the described proteins to Mga, M, and M-like proteins and the response t o elevated level of CO2, we suggest that the dmg and dem genes are members of a regulon similar to the described mga regulon in S. pyogenes, which enc odes several virulence factors in this species.