| Co-Investigator(Kenkyū-buntansha) |
KAWABATA Shigetada Osaka University, Graduate School of Dentistry, Associate Professor, 大学院・歯学研究科, 助教授 (50273694)
NAKAGAWA Ichiro Osaka University, Graduate School of Dentistry, Assistant Professor, 大学院・歯学研究科, 講師 (70294113)
岡本 成史 大阪大学, 大学院・歯学研究科, 助手 (50311759)
|
|---|
| Budget Amount *help |
¥50,180,000 (Direct Cost: ¥38,600,000、Indirect Cost: ¥11,580,000)
Fiscal Year 2004: ¥8,190,000 (Direct Cost: ¥6,300,000、Indirect Cost: ¥1,890,000)
Fiscal Year 2003: ¥17,810,000 (Direct Cost: ¥13,700,000、Indirect Cost: ¥4,110,000)
Fiscal Year 2002: ¥24,180,000 (Direct Cost: ¥18,600,000、Indirect Cost: ¥5,580,000)
|
|---|
| Research Abstract |
Group A streptococcus(GAS) is a gram-positive bacterial pathogen that causes various suppurative infections and nonsuppurative sequelae. Since the late 1980s, streptococcal toxic-shock like syndrome(STSS) and severe invasive GAS infections have been reported globally. Here we sequenced the genome of serotype M3 strain SSI-1, isolated from an STSS patient in Japan, and compared it with those of other GAS strains. The SSI-1 genome is composed of 1,884,275 bp, and 1.7 Mb of the sequence is highly conserved relative to strain SF370 (serotype M1) and MGAS8232 (serotype M18), and almost completely conserved relative to strain MGAS315 (serotype M3). However, a large genomic rearrangement has been shown to occur across the replication axis between the homologous rrn-comX1 regions and between two prophage-coding regions across the replication axis. This genomic rearrangement occurs in 65% of clinical isolates (64/94) collected after 1990, whereas it is found in only 25% of clinical isolates (7/
… More
28) collected before 1985. These observations indicate that streptococcal phages represent important plasticity regions in the GAS chromosome where recombination between homologous phage genes can occur and result not only in new phage derivatives, but also in large chromosomal rearrangements.
GAS expresses a wide variety of structural and enzyme proteins that are associated with the bacterial cell wall. It has been demonstrated that several surface proteins have binding abilities to human host proteins, such as fibronectin(Fn), laminin, plasmin, collagen, immunoglobulins, and C4b. Fn-binding proteins of GAS have also been reported to be adhesins and invasins, including protein F1/SfbI, protein F2, SfbII/SOF, PFBP, and Fba (renamed FbaA). By searching the whole genome sequence of an M3 strain from a TSLS patient, an open reading frame was found among the putative surface proteins. It possessed an LPXTG motif and Fn-binding repeat domains in the C-terminal region and was designated as FbaB (Fn-binding protein of group A streptococci type B). The fbaB gene was found in all M3 and M18 strains examined, although not in other M serotypes. Furthermore, FbaB protein was expressed on the cell surface of TSLS strains but not on non-TSLS ones. Enzyme-linked immunosorbent assay and ligand blotting revealed that recombinant FbaB exhibits a strong Fn-binding ability. An FbaB-deficient mutant strain showed 6-fold lower adhesion and invasion efficiencies to HEp-2 cells than the wild type. Moreover, mortality was decreased in mice infected with the mutant strain in comparison to the wild type. These data suggest that FbaB is etiologically involved in the development of invasive streptococcal diseases.
The apparent worldwide resurgence of invasive Streptococcus pyogenes infection in the last two decades remains unexplained. At present, animal models in which toxic shock-like syndrome or necrotizing fasciitis is induced after S.pyogenes infection are not well developed. We demonstrate here that infection with a nonlethal dose of influenza A virus 2 days before intranasal infection with a nonlethal dose of S.pyogenes strains led to a death rate of more than 90% in mice, 10% of which showed necrotizing fasciitis. Infection of lung alveolar epithelial cells by the influenza A virus resulted in viral hemagglutinin expression on the cell surface and promoted internalization of S.pyogenes. However, treatment with monoclonal antibodies to hemagglutinin markedly decreased this internalization. Our results indicate that prior infection with influenza A virus induces a lethal synergism, resulting in the induction of invasive S.pyogenes infection in mice.
We found that the autophagic machinery could effectively eliminate pathogenic group A Streptococcus(GAS) within nonphagocytic cells. After escaping from endosomes into the cytoplasm, GAS became enveloped by autophagosome-like compartments and were killed upon fusion of these compartments with lysosomes. In autophagy-deficient Atg5-/- cells, GAS survived, multiplied, and were released from the cells. Thus, the autophagic machinery can act as an innate defense system against invading pathogens. Less
|
