Adhesion determinants of the Streptococcus species.
Bottom Line: Phylogenetic analyses based on 16S rRNA sequences of the streptococcal species reveal a clustering pattern, reflecting, with a few exceptions, their pathogenic potential and ecological preferences.Bacterial adhesins recognize and bind cell surface molecules and extracellular matrix components through specific domains that for certain adhesin families have been well defined and found conserved across the streptococcal species.In this review, we present the different streptococcal adhesin families categorized on the basis of their adhesive properties and structural characteristics, and, when available, we focus the attention on conserved functional domains.
Affiliation: Novartis Vaccines and Diagnostics, Via Fiorentina 1, Siena, Italy.Show MeSH
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Mentions: The nomenclature of Streptococcus species is rather complex as it is not only based on the species names but, for historical reasons, designations are used that are based on haemolysis type or serological grouping. In particular, Lancefield typing based on specific antisera against ‘group‐specific’ carbohydrate or lipoteichoic acid (Group D) antigens has been and is widely used to classify beta‐haemolytic streptococci. As an example it turned out, however, that S. pyogenes, for which often the terminus GAS (group A Streptococcus) is used as a synonym, is not the only Streptococcus that may possess the group A antigen because also S. anginosus or S. dysgalactiae ssp. equisimilis may carry the A antigen. On the other hand, a given streptococcal species may have several diverse types of Lancefield antigen e.g. Streptococcus dysgalactiae ssp. equisimilis may be a carrier of A, C, G or L antigens (Facklam, 2002). In the last decades phylogenetic typing based on 16S rRNA (Fig. 1) has helped the accurate identification of bacterial isolates and the discovery of novel bacteria in clinical microbiology laboratories to form a clearer picture of streptococcal species relationships. In Fig. 1 we identified in the genus Streptococcus five major clusters: S. mitis, S. mutans, S. salivarius (viridians streptococci), S. agalactiae and S. pyogenes (pyogenic group). This analysis reveals a clustering pattern reflecting the pathogenic potential and ecological preferences of the streptococcal species (Kawamura et al., 1995). One exception is the mitis group, which contains one of the leading pathogens, S. pneumoniae, along with other species that are prototype commensals of the upper respiratory tract (such as S. mitis, S. oralis or S. infantis). Recent works (Kilian et al., 2008; Bishop et al., 2009) propose the use of concatenated sequences of conserved housekeeping genes in addition to the analysis of presence/absence of virulence‐specific genes to better assign newly discovered atypical isolates, identify eventual new species, discriminate between species that are really close in terms of 16S rRNA sequences, and define in this way a standard taxonomic procedure for the genus Streptococcus.
Affiliation: Novartis Vaccines and Diagnostics, Via Fiorentina 1, Siena, Italy.