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Rise and persistence of global M1T1 clone of Streptococcus pyogenes.

Aziz RK, Kotb M - Emerging Infect. Dis. (2008)

Bottom Line: Among these strains is a highly virulent subclone of serotype M1T1 that has exhibited unusual epidemiologic features and virulence, unlike all other streptococcal strains.Because of its unusual prevalence, global spread, and increased virulence, we investigated the unique features that likely confer its unusual properties.In doing so, we found that the increased virulence of this clonal strain can be attributed to its diversification through phage mobilization and its ability to sense and adapt to different host environments; accordingly, the fittest members of this diverse bacterial community are selected to survive and invade host tissue.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiologyand Immunology, Cairo University, Cairo, Egypt. ramy.aziz@salmonella.org

ABSTRACT
The resurgence of severe invasive group A streptococcal infections in the 1980s is a typical example of the reemergence of an infectious disease. We found that this resurgence is a consequence of the diversification of particular strains of the bacteria. Among these strains is a highly virulent subclone of serotype M1T1 that has exhibited unusual epidemiologic features and virulence, unlike all other streptococcal strains. This clonal strain, commonly isolated from both noninvasive and invasive infection cases, is most frequently associated with severe invasive diseases. Because of its unusual prevalence, global spread, and increased virulence, we investigated the unique features that likely confer its unusual properties. In doing so, we found that the increased virulence of this clonal strain can be attributed to its diversification through phage mobilization and its ability to sense and adapt to different host environments; accordingly, the fittest members of this diverse bacterial community are selected to survive and invade host tissue.

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Similarities and differences between the 4 highly related prophages 5005.2, 370.3, MemPhiS, and 315.3. The figure, generated by the SEED comparison tools (22) (http://theseed.uchicago.edu), shows the physical maps of the 4 prophages near their attachment sites. Arrows with identical colors designate orthologous genes; those in gray designate alternative alleles of the genes. p, prx; mf, mitogenic factor; cadA, heavy metal/cadmium transporter ATPase; GAS, group A streptococci.
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Figure 2: Similarities and differences between the 4 highly related prophages 5005.2, 370.3, MemPhiS, and 315.3. The figure, generated by the SEED comparison tools (22) (http://theseed.uchicago.edu), shows the physical maps of the 4 prophages near their attachment sites. Arrows with identical colors designate orthologous genes; those in gray designate alternative alleles of the genes. p, prx; mf, mitogenic factor; cadA, heavy metal/cadmium transporter ATPase; GAS, group A streptococci.

Mentions: The M1T1 prophages exhibit considerable genetic mosaicism, and the sequence analysis of the 2 novel M1T1 phages demonstrates that these bacterial viruses continuously exchange functional modules by various genetic mechanisms, including different modes of recombination (19). We believe that exchange between the lysis and lysogenic conversion modules of GAS prophages has led to the swapping of virulence genes (toxins) among phages (19). We also believe that this process is facilitated by a highly conserved gene, paratox (prx), commonly found between the toxin gene and phage attachment site. Conserved prx sequences on 1 side of the toxin gene together with 1–3 highly conserved phage genes on the other side (lysin, holin, and/or hyaluronidase genes) are likely to facilitate recombination events leading to swapping of toxin genes among bacterial isolates (Figure 1) (19). This notion is supported by the fact that strains belonging to the same serotype may have different virulence components carried by the same or highly similar phages, whereas those belonging to different serotypes may, in fact, have identical phage-encoded toxins. For example, 4 highly similar phages (370.3, 5005.2, MemPhiS, 315.3) identified in M1 SF370, M1T1 5005, M1T1 6050, and M3 strains, respectively, have different DNases in their lysogenic conversion modules. Phages 370.3 and 5005.2 are >99% identical to each other and carry the mf3 gene, and each is 90% identical to MemPhiS and 315.3, which carry the mf4 gene instead (Figure 2).


Rise and persistence of global M1T1 clone of Streptococcus pyogenes.

Aziz RK, Kotb M - Emerging Infect. Dis. (2008)

Similarities and differences between the 4 highly related prophages 5005.2, 370.3, MemPhiS, and 315.3. The figure, generated by the SEED comparison tools (22) (http://theseed.uchicago.edu), shows the physical maps of the 4 prophages near their attachment sites. Arrows with identical colors designate orthologous genes; those in gray designate alternative alleles of the genes. p, prx; mf, mitogenic factor; cadA, heavy metal/cadmium transporter ATPase; GAS, group A streptococci.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2609857&req=5

Figure 2: Similarities and differences between the 4 highly related prophages 5005.2, 370.3, MemPhiS, and 315.3. The figure, generated by the SEED comparison tools (22) (http://theseed.uchicago.edu), shows the physical maps of the 4 prophages near their attachment sites. Arrows with identical colors designate orthologous genes; those in gray designate alternative alleles of the genes. p, prx; mf, mitogenic factor; cadA, heavy metal/cadmium transporter ATPase; GAS, group A streptococci.
Mentions: The M1T1 prophages exhibit considerable genetic mosaicism, and the sequence analysis of the 2 novel M1T1 phages demonstrates that these bacterial viruses continuously exchange functional modules by various genetic mechanisms, including different modes of recombination (19). We believe that exchange between the lysis and lysogenic conversion modules of GAS prophages has led to the swapping of virulence genes (toxins) among phages (19). We also believe that this process is facilitated by a highly conserved gene, paratox (prx), commonly found between the toxin gene and phage attachment site. Conserved prx sequences on 1 side of the toxin gene together with 1–3 highly conserved phage genes on the other side (lysin, holin, and/or hyaluronidase genes) are likely to facilitate recombination events leading to swapping of toxin genes among bacterial isolates (Figure 1) (19). This notion is supported by the fact that strains belonging to the same serotype may have different virulence components carried by the same or highly similar phages, whereas those belonging to different serotypes may, in fact, have identical phage-encoded toxins. For example, 4 highly similar phages (370.3, 5005.2, MemPhiS, 315.3) identified in M1 SF370, M1T1 5005, M1T1 6050, and M3 strains, respectively, have different DNases in their lysogenic conversion modules. Phages 370.3 and 5005.2 are >99% identical to each other and carry the mf3 gene, and each is 90% identical to MemPhiS and 315.3, which carry the mf4 gene instead (Figure 2).

Bottom Line: Among these strains is a highly virulent subclone of serotype M1T1 that has exhibited unusual epidemiologic features and virulence, unlike all other streptococcal strains.Because of its unusual prevalence, global spread, and increased virulence, we investigated the unique features that likely confer its unusual properties.In doing so, we found that the increased virulence of this clonal strain can be attributed to its diversification through phage mobilization and its ability to sense and adapt to different host environments; accordingly, the fittest members of this diverse bacterial community are selected to survive and invade host tissue.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiologyand Immunology, Cairo University, Cairo, Egypt. ramy.aziz@salmonella.org

ABSTRACT
The resurgence of severe invasive group A streptococcal infections in the 1980s is a typical example of the reemergence of an infectious disease. We found that this resurgence is a consequence of the diversification of particular strains of the bacteria. Among these strains is a highly virulent subclone of serotype M1T1 that has exhibited unusual epidemiologic features and virulence, unlike all other streptococcal strains. This clonal strain, commonly isolated from both noninvasive and invasive infection cases, is most frequently associated with severe invasive diseases. Because of its unusual prevalence, global spread, and increased virulence, we investigated the unique features that likely confer its unusual properties. In doing so, we found that the increased virulence of this clonal strain can be attributed to its diversification through phage mobilization and its ability to sense and adapt to different host environments; accordingly, the fittest members of this diverse bacterial community are selected to survive and invade host tissue.

Show MeSH
Related in: MedlinePlus