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Infection and Immunity, October 2000, p. 5610-5618, Vol. 68, No. 10
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Identification of Group B Streptococcal Sip Protein, Which Elicits Cross-Protective Immunity

Bernard R. Brodeur,* Martine Boyer, Isabelle Charlebois, Josée Hamel, France Couture, Clément R. Rioux,dagger and Denis Martin

Unité de Recherche en Vaccinologie, Centre Hospitalier Universitaire de Québec, et Université Laval, Ste-Foy, Canada G1V 4G2

Received 19 May 2000/Returned for modification 29 June 2000/Accepted 17 July 2000

A protein of group B streptococci (GBS), named Sip for surface immunogenic protein, which is distinct from previously described surface proteins, was identified after immunological screening of a genomic library. Immunoblots using a Sip-specific monoclonal antibody indicated that a protein band with an approximate molecular mass of 53 kDa which did not vary in size was present in every GBS strain tested. Representatives of all nine GBS serotypes were included in the panel of strains. Cloning and sequencing of the sip gene revealed an open reading frame of 1,305 nucleotides coding for a polypeptide of 434 amino acid residues, with a calculated pI of 6.84 and molecular mass of 45.5 kDa. Comparison of the nucleotide sequences from six different strains confirmed with 98% identity that the sip gene is highly conserved among GBS isolates. N-terminal amino acid sequencing also indicated the presence of a 25-amino-acid signal peptide which is cleaved in the mature protein. More importantly, immunization with the recombinant Sip protein efficiently protected CD-1 mice against deadly challenges with six GBS strains of serotypes Ia/c, Ib, II/R, III, V, and VI. The data presented in this study suggest that this highly conserved protein induces cross-protective immunity against GBS infections and emphasize its potential as a universal vaccine candidate.

* Corresponding author. Mailing address: Unité de Recherche en Vaccinologie, Centre Hospitalier Universitaire de Québec, Pavillon CHUL, Édifice T-367, 2705 Boul. Laurier, Ste-Foy, Québec, Canada G1V 4G2. Phone: (418) 656-4141-6266. Fax: (418) 654-2280. E-mail: Bernard.Brodeur{at}crchul.ulaval.ca.

dagger Present address: Intellivax International Inc., Ville St-Laurent, Quebec, Canada H4S 2A1.

Infection and Immunity, October 2000, p. 5610-5618, Vol. 68, No. 10
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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