Contribution of Streptococcus anginosus to infections caused by groups C and G streptococci, southern India.

Vellore, a region in southern India, has a high incidence of severe human infections with Beta-hemolytic group C and G streptococci (GCGS). To determine the causative species in these infections, we conducted 16S rRNA gene sequencing: Streptococcus dysgalactiae subsp. equisimilis (81%) and S. anginosus (19%) were the causative organisms in the 2-year study period (2006-2007). We used PCR to detect the virulence-related emm gene; results showed that it was restricted to S. dysgalactieae subsp. equisimilis isolates of 99.2% tested positive. Due to a novel marker, S. anginosus and S. constellatus can be quickly and accurately distinguished from other members of the genus. The notable contribution of the anginosus group to human infections suggests that this group of obligate pathogens deserves more attention in healthcare and research.

Region specific and worldwide distribution of collagen-binding M proteins with PARF motifs among human pathogenic streptococcal isolates.

Some of the variety of Streptococcus pyogenes and Streptococcus dysgalactiae ssp. equisimilis (SDSE) M proteins act as collagen-binding adhesins that facilitate acute infection. Moreover, their potential to trigger collagen autoimmunity has been implicated in the pathogenesis of acute rheumatic fever and attributed to a collagen-binding motif called PARF (peptide associated with rheumatic fever). For the first time we determine the rate of clinical isolates with collagen-binding M proteins that use a PARF motif (A/T/E)XYLXX(L/F)N in a defined geographic region, Vellore in South India. In this region both, incidence of streptococcal infections and prevalence of acute rheumatic fever are high. M proteins with PARF motif conferred collagen-binding activity to 3.9% of 153 S. pyogenes and 10.6% of 255 SDSE clinical isolates from Vellore. The PARF motif occurred in three S. pyogenes and 22 SDSE M protein types. In one of the S. pyogenes and five of the SDSE M proteins that contained the motif, collagen-binding was impaired, due to influences of other parts of the M protein molecule. The accumulated data on the collagen binding activity of certain M protein types allowed a reanalysis of published worldwide emm-typing data with the aim to estimate the rates of isolates that bind collagen via PARF. The results indicate that M proteins, which bind collagen via a PARF motif, are epidemiologically relevant in human infections, not only in Vellore. It is imperative to include the most relevant collagen-binding M types in vaccines. But when designing M protein based vaccines it should be considered that collagen binding motifs within the vaccine antigen remain potential risk factors.

Group G streptococcal IgG binding molecules FOG and protein G have different impacts on opsonization by C1q.

Recent epidemiological data on diseases caused by beta-hemolytic streptococci belonging to Lancefield group C and G (GCS, GGS) underline that they are an emerging threat to human health. Among various virulence factors expressed by GCS and GGS isolates from human infections, M and M-like proteins are considered important because of their anti-phagocytic activity. In addition, protein G has been implicated in the accumulation of IgG on the bacterial surface through non-immune binding. The function of this interaction, however, is still unknown. Using isogenic mutants lacking protein G or the M-like protein FOG (group G streptococci), respectively, we could show that FOG contributes substantially to IgG binding. A detailed characterization of the interaction between IgG and FOG revealed its ability to bind the Fc region of human IgG and its binding to the subclasses IgG1, IgG2, and IgG4. FOG was also found to bind IgG of several animal species. Surface plasmon resonance measurements indicate a high affinity to human IgG with a dissociation constant of 2.4 pm. The binding site was localized in a central motif of FOG. It has long been speculated about anti-opsonic functions of streptococcal Fc-binding proteins. The presented data for the first time provide evidence and, furthermore, indicate functional differences between protein G and FOG. By obstructing the interaction between IgG and C1q, protein G prevented recognition by the classical pathway of the complement system. In contrast, IgG that was bound to FOG remained capable of binding C1q, an effect that may have important consequences in the pathogenesis of GGS infections.

Identification of a streptococcal octapeptide motif involved in acute rheumatic fever.

Acute rheumatic fever is a serious autoimmune sequela of pharyngitis caused by certain group A streptococci. One mechanism applied by streptococcal strains capable of causing acute rheumatic fever is formation of an autoantigenic complex with human collagen IV. In some geographic regions with a high incidence of acute rheumatic fever pharyngeal carriage of group C and group G streptococci prevails. Examination of such strains revealed the presence of M-like surface proteins that bind human collagen. Using a peptide array and recombinant proteins with targeted amino acid substitutions, we could demonstrate that formation of collagen complexes during streptococcal infections depends on an octapeptide motif, which is present in collagen binding M and M-like proteins of different beta-hemolytic streptococcal species. Mice immunized with streptococcal proteins that contain the collagen binding octapeptide motif developed high serum titers of anti-collagen antibodies. In sera of rheumatic fever patients such a collagen autoimmune response was accompanied by specific reactivity against the collagen-binding proteins, linking the observed effect to clinical cases. Taken together, the data demonstrate that the identified octapeptide motif through its action on collagen plays a crucial role in the pathogenesis of rheumatic fever. Eradication of streptococci that express proteins with the collagen binding motif appears advisable for controlling rheumatic fever.