Rise and persistence of global M1T1 clone of Streptococcus pyogenes

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.

Figure 1

Suggested model for toxin mobilization between phages, reprinted from Aziz et al. (19). Recombination hot spots on both sides of the toxin genes are shown: one is prx (paratox), and the other may be lys (lysin), hol (holin), or hylP (phage hyaluronidase).

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.