Lateral transfer of alpha-like protein gene cassettes among streptococci: identification of a new family member in Streptococcus dysgalactiae subsp. equisimilis

Sir—The Alp (alpha‐like protein) family comprises the surface‐localized protein antigens of Streptococcus agalactiae (GBS) Alpha‐C, Alp1–4, Rib/R4 that have a mosaic structure and contain large internal tandem repeats (Bröker and Spelleberg 2004; Lindahl et al. 2005). The prototype of this family, the alpha‐C protein, has been demonstrated to be implicated in the adhesion and invasion of S. agalactiae to epithelial cells by interaction with host glycosaminoglycans (Bolduc et al. 2002; Baron et al. 2004) and in virulence in a mouse model of GBS sepsis (Li et al. 1997). Here we describe, for the first time, the identification of a new member of the Alp protein family (a mosaic between Rib and Alp2) in a different streptococcal species, Streptococcus dysgalactiae subsp. equisimilis. During an enhanced national surveillance for invasive diseases caused by beta‐haemolytic streptococci we received a strain, referred as S. agalactiae, isolated from an endovascular catheter infection. By using a multiplex PCR for the direct identification of the Alp protein genes (Creti et al. 2004), we obtained an amplified product indicative of the presence of a rib gene, whose identity was confirmed by amplicon sequencing. However, further protocols for species confirmation, like grouping agglutination test (Dryspot Strep Grouping Kit, Oxoid), did not support the identification of the strain as S. agalactiae but were suggestive of a group G Streptococcus. Subsequent analyses by using the API 32 Strep system (bioMerieux, Lyon, France) and sequencing of the 16S ribosomal DNA gene definitively identified the strain as S. dysgalactiae subsp. equisimilis.