Regulation of protein H expression in M1 serotype isolates ofStreptococcus pyogenes

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Abstract
Protein H is an immunoglobulin-binding protein expressed by certain M1 serotypes of Streptococcus pyogenes. In a recent study of invasive group A isolates, it was found that none of the 16 M1 serotype isolates analyzed expressed protein H on their surface despite the presence of the protein H gene (sph) in approximately one-third of the isolates. Selection of stable protein H-expressing variants could be achieved by infection of prtH+ non-expressing strains into a mouse skin and recovering bacteria from the spleen. This effect was independent of the transcription regulator Mga, since a similar effect was noted in an mga− mutant. Thus, host passage of S. pyogenes can lead to stable high level expression of Protein H.