Role of CsrR, Hyaluronic Acid, and SpeB in the Internalization ofStreptococcus pyogenesM Type 3 Strain by Epithelial Cells

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Abstract
Internalization of group A streptococcus by human epithelial cells has been extensively studied during the past 6 years. It is now clear that multiple mechanisms are involved in this process. We have previously demonstrated that the CsrR global regulator controls the internalization of an invasive M type 3 strain through regulation of thehas(hyaluronic acid synthesis) operon, as well as another, unknown gene(s). Recently, it was reported that the CsrR-regulated cysteine protease (SpeB) is also involved in bacterial uptake. In this study we have examined the roles of CsrR, hyaluronic acid capsule, and SpeB in streptococcal internalization. We have constructed isogenic mutants of the M3 serotype deficient in thecsrR,hasA, andspeBgenes and tested their ability to be internalized by HEp-2 epithelial cells. Inactivation ofcsrRabolished internalization, while inactivation of eitherhasAorspeBincreased the internalization efficiency. Mutation incsrRderepressedhasAtranscription and lowered the activity of SpeB, while no effect onspeBtranscription was observed. ThespeBmutant expressed smaller amounts of capsule, while thehasAmutant transcribed morecsrRandspeBmRNAs. Thus, it seems that complex interactions between CsrR, SpeB, and capsule are involved in modulation of group A streptococcus internalization.