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Infection and Immunity, January 2000, p. 294-302, Vol. 68, No. 1
0019-9567/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

M-Like Proteins of Streptococcus dysgalactiae

József Vasi, Lars Frykberg, Lena E. Carlsson, Martin Lindberg, and Bengt Guss*

Department of Microbiology, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden

Received 9 July 1999/Returned for modification 27 August 1999/Accepted 14 October 1999

Streptococcus dysgalactiae is one of the most important bacterial species isolated from bovine mastitis. To identify potential virulence factors of this species we prepared chromosomal DNA from strain 8215 and constructed a phage display library. By affinity selection of the library against fibrinogen (Fg), we isolated and characterized a gene, called demA, encoding a protein with the molecular mass of ~58 kDa, called DemA, displaying both plasma protein binding properties and sequence similarities with the M and M-like proteins of other streptococcal species. Purified recombinant DemA protein was found to completely inhibit Fg-binding to cells of S. dysgalactiae. A continued sequence analysis revealed that the demA gene was preceded by an open reading frame (dmgA) coding for a putative protein, called DmgA, with high similarities to the Mga proteins of Streptococcus pyogenes. By additional cloning, the corresponding dmgA and demA genes from another strain, called Epi9, were isolated and analyzed. These genes, called dmgB and demB, respectively, revealed a high degree of similarity to the corresponding 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 transcription of the demB gene as shown in a Northern blot. Strain 8215 did not respond 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 to 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 encodes several virulence factors in this species.

* Corresponding author. Mailing address: Department of Microbiology, Swedish University of Agricultural Sciences, Box 7025, S-750 07 Uppsala, Sweden. Phone: 46 18 673205. Fax: 46 18 673392. E-mail: Bengt.Guss{at}mikrob.slu.se.

Infection and Immunity, January 2000, p. 294-302, Vol. 68, No. 1
0019-9567/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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