The dynamic Alp landscape of Streptococcus dysgalactiae.

BACKGROUND

Streptococcus dysgalactiae is an important pathogen in both humans and animals. Alpha-like proteins (Alps) are surface-anchored adhesins and contribute to host tissue invasion. While Alps are nearly ubiquitous in Streptococcus agalactiae and are recognized as major virulence factors in Streptococcus pyogenes, their presence and diversity in S. dysgalactiae remain poorly characterized.

METHODS

We screened 1,243 S. dysgalactiae genomes of human and animal origin from Norway, Japan, Canada, and Australia for presence of alp genes. A subset of 32 strains from Norway was further sequenced using long-read technology (Nanopore) to resolve tandem repeat regions of alp genes.

RESULTS

By screening global strain collections, we found five novel alp genes, designated here as dysalp2-5 and alp1-3 hybrid. The alp genes exhibited extensive genetic heterogeneity, predominantly arising from mosaicism and tandem repeat variations. Overall, alp genes were detected in 18% of human and 10-15% of animal strains. There were geographic differences in prevalence and diversity of alp genes, yet the overall distribution did not follow a strictly clonal pattern. The alp genes in S. dysgalactiae resided on mobile genetic elements, and we detected similar elements also in other streptococcal species.

CONCLUSION

We reveal that Alpha-like proteins are common and widely distributed among S. dysgalactiae, and exhibit extensive genetic heterogeneity. Our findings expand our understanding of Alp diversity and shed light on the evolutionary mechanisms that drive cross-species exchange of alp genes.