Relationships between <it>emm </it>and multilocus sequence types within a global collection of <it>Streptococcus pyogenes</it>

• Main Authors: McGregor Karen F, Bessen Debra E, Whatmore Adrian M
• Format: Article
• Language: English
• Published: BMC 2008-04-01
• Series: BMC Microbiology
• Online Access: http://www.biomedcentral.com/1471-2180/8/59

<p>Abstract</p> <p>Background</p> <p>The M type-specific surface protein antigens encoded by the 5' end of <it>emm </it>genes are targets of protective host immunity and attractive vaccine candidates against infection by <it>Streptococcus pyogenes</it>, a global human pathogen. A history of genetic change in <it>emm </it>was evaluated for a worldwide collection of > 500 <it>S. pyogenes </it>isolates that were defined for genetic background by multilocus sequence typing of housekeeping genes.</p> <p>Results</p> <p>Organisms were categorized by genotypes that roughly correspond to throat specialists, skin specialists, and generalists often recovered from infections at either tissue site. Recovery of distant clones sharing the same <it>emm </it>type was ~4-fold higher for skin specialists and generalists, as compared to throat specialists. Importantly, <it>emm </it>type was often a poor marker for clone. Recovery of clones that underwent recombinational replacement with a new <it>emm </it>type was most evident for the throat and skin specialists. The average ratio of nonsynonymous substitutions per nonsynonymous site (Ka) and synonymous substitutions per synonymous site (Ks) was 4.9, 1.5 and 1.3 for <it>emm </it>types of the throat specialist, skin specialist and generalist groups, respectively.</p> <p>Conclusion</p> <p>Data indicate that the relationships between <it>emm </it>type and genetic background differ among the three host tissue-related groups, and that the selection pressures acting on <it>emm </it>appear to be strongest for the throat specialists. Since positive selection is likely due in part to a protective host immune response, the findings may have important implications for vaccine design and vaccination strategies.</p>