drs (Distantly related sic) gene polymorphisms among emm12-type Streptococcus pyogenes isolates

Sequence diversity of sicG among group C and G Streptococcus dysgalactiae subspecies equisimilis isolates associated with human infections in western Norway

Streptococcal inhibitor of complement (SIC) and distantly related to SIC (DRS) are well-characterized extracellular virulence factors produced by only a few emm types among group A streptococci. The prevalence and sequence variations of the sic-like gene (sicG) in clinical samples of group C and G Streptococcus dysgalactiae subspecies equisimilis (SDSE), however, have not been widely investigated. We constructed primers targeting sicG and screened 129 geographically matched and previously emm-typed non-invasive (n = 64) and invasive (n = 65) SDSE isolates for the presence of this gene. sicG was detected in seven non-invasive and eight invasive isolates belonging to eight different emm types. Within five of these emm types, sicG-negative isolates were also detected. All three isolates of stG2078.0 possessed sicG and were associated with severe soft tissue infections. Altogether, six sicG alleles (sicG1-6) were identified, and sequence variations were mainly caused by single nucleotide polymorphisms and deletion/insertion mutations. sicG1-6 were predicted to encode SICG proteins of varying length, composition, and homology with SIC and DRS proteins of group A streptococci. Our findings indicate an unpredictable association between sicG and emm type, a limited distribution and substantial sequence diversity of sicG, and no obvious relation between its presence and disease severity.

Prevalence of a streptococcal inhibitor of a complement-mediated cell lysis-like gene (sicG) in Streptococcus dysgalactiae subsp. equisimilis

Streptococcus dysgalactiae subsp. equisimilis isolates (n = 110) were analyzed by PCR to determine whether the gene encoding SICG, a homolog of Streptococcus pyogenes SIC, was present. Nineteen strains (17%) had this gene of which 11 (55%) were isolated from patients with invasive disease. All 19 strains possessed group G carbohydrate. Molecular characterization of emm type revealed that the majority of emm sequences were stG643 and stG2078. Only the N-terminal sequence of SICG was similar to that of SIC in S. pyogenes. Although we found no significant relationship between pathogenic severity and sicG possession, further investigation into the mechanism of SICG may elucidate the virulence in S. dysgalactiae subsp. equisimilis infection.

Streptococcal DRS (distantly related to SIC) and SIC inhibit antimicrobial peptides, components of mucosal innate immunity: a comparison of their activities

"Streptococcal inhibitor of complement" (SIC) and "distantly related to SIC" (DRS) are related virulence factors secreted by M1 and M12 strains of GAS, respectively. The human mucosal innate immune system, important components of which are beta-defensins, secretory leukocyte proteinase inhibitor (SLPI) and lysozyme, provides the first line of defence against microorganisms. We report the interaction between DRS and these proteins; further investigations into the interaction of SIC with the beta-defensins; and compare the sensitivity of M12 and M1 GAS to SLPI. We show that SLPI, which kills M1 GAS and is inhibited by SIC, cannot kill M12 GAS. DRS cannot inhibit SLPI killing of M1 GAS, although ELISA shows binding of DRS to SLPI. We suggest that the target for SLPI on M1 GAS resembles SIC, and soluble SIC inhibits by acting as a decoy for SLPI. M12 GAS may not have this target and cannot interact with SLPI. DRS inhibits the antibacterial action of hBD-2 and hBD-3. Binding of both SIC and DRS to hBD-2, and DRS to hBD-3, shows small positive enthalpy, suggesting that binding is largely hydrophobic. The data for SIC and hBD-3 indicate that this is not a homogeneous bimolecular interaction. We conclude that DRS shares several of the properties of SIC, and therefore can be considered an important virulence factor of M12 GAS and an aid to colonization of the host mucosae.

DRS is far less divergent than streptococcal inhibitor of complement of group A streptococcus

When 100 group A streptococcus isolates were screened, drs, a variant of sic, was identified in emm12 and emm55 isolates. Molecular characterization showed that the drs gene sequence is highly conserved, unlike the sic gene sequence. However, the variation in gene size observed was due to the presence of extra internal repeat sequences.

Inhibition of antimicrobial peptides by group A streptococci: SIC and DRS

SIC (streptococcal inhibitor of complement) is a 31 kDa protein secreted by a few highly virulent strains of GAS (group A streptococci), predominantly by the M1 strain. Initially described as an inhibitor of the membrane attack complex of complement, it has turned out to be a polyfunctional inhibitor of the innate mucosal immune response. The SIC protein sequence contains three domains: an N-terminal SRR (short repeat region), followed by three longer tandem repeats [LRR (long repeat region)] and a C-terminal PRR (proline-rich region). SIC inhibits the antibacterial activity of a wide range of antimicrobial peptides and proteins: i.e. lysozyme, SLPI (secretory leucocyte proteinase inhibitor), LL-37, hNP-1 (human neutrophil peptide-1) and the human β-defensins 1, 2 and 3. Analysis of the functional properties of recombinant domains of SIC shows that binding and inhibition of lysozyme and human β-defensin-3 require the SRR+LRR, as does binding to SLPI. Complement inhibition is confined to the SRR. M12 GAS secrete a protein ‘distantly related to SIC’ (DRS). DRS contains a C-terminal PRR which is significantly similar to that of SIC, but it has no central LRR and the N-terminal SRR is very different. DRS inhibits human β-defensin-3, but has no effect on lysozyme, SLPI or complement.

Molecular heterogeneity among north Indian isolates of Group A Streptococcus

AIM

To monitor molecular heterogeneity among the clinical isolates of group A Streptococcus (GAS) from north India by Vir and emm typing.

METHODS AND RESULTS

GAS isolates, 31 from pharyngitis and nine from rheumatic fever (RF)/rheumatic heart disease (RHD) patients were differentiated into 16 Vir types (VT). These isolates were further discriminated into 23 emm types. Most of emm types were Vir type specific, except few (7.5%), which revealed different Vir types within same emm type. The most prevalent emm type found was emm 49 (15%) followed by 7.5% of emm 69, emm 71 and emm 75 which were different from emm type distribution reported from south India.

CONCLUSIONS

Analysis of data revealed 40% heterogeneity by Vir typing and 57.5% by emm typing among GAS isolates which is significant in view of small number of isolates studied. SIGNIFICANCE OF IMPACT OF THE STUDY: The molecular study for the first time demonstrates different emm types prevalent and circulating in northern region of India and such data may help in selection of types for vaccine development.