Natural Variation in the Promoter of the Gene Encoding the Mga Regulator Alters Host-Pathogen Interactions in Group A Streptococcus Carrier Strains

Abstract

cHumans commonly carry pathogenic bacteria asymptomatically, but the molecular factors underlying microbial asymptomatic carriage are poorly understood. We previously reported that two epidemiologically unassociated serotype M3 group A Streptococcus (GAS) carrier strains had an identical 12-bp deletion in the promoter of the gene encoding Mga, a global positive gene regulator. Herein, we report on studies designed to test the hypothesis that the identified 12-bp deletion in the mga promoter alters GAS virulence, thereby potentially contributing to the asymptomatic carrier phenotype. Using allelic exchange, we introduced the variant promoter into a serotype M3 invasive strain and the wild-type promoter into an asymptomatic carrier strain. Compared to strains with the wild-type mga promoter, we discovered that strains containing the promoter with the 12-bp deletion produced significantly fewer mga and Mga-regulated gene transcripts. Consistent with decreased mga transcripts, strains containing the variant mga promoter were also significantly less virulent in in vivo and ex vivo models of GAS disease. Further, we provide evidence that the pleiotropic regulator protein CodY binds to the mga promoter and that the 12-bp deletion in the mga promoter reduces CodY-mediated mga transcription. We conclude that the naturally occurring 12-bp deletion in the mga promoter significantly alters the pathogen-host interaction of these asymptomatic carrier strains. Our findings provide new insight into the molecular basis of the carrier state of an important human pathogen.

Natural Variant of Collagen-Like Protein A in Serotype M3 Group A Streptococcus Increases Adherence and Decreases Invasive Potential

“…We previously showed that peak sclA transcript coincides with peak mga transcript levels in serotype M3 GAS (15). Thus, we hypothesized that sclA transcript would be produced in a strain with either sclA Invasive or sclA Carrier .…”

“…The transcript levels of sclA were assayed as previously described (15). Briefly, RNA was isolated and purified by using an RNeasy kit according to the manufacturer's instructions (Qiagen).…”

“…Plasmids and primers used in the present study are listed in Tables S1 and S2 in the supplemental material. The procedure used in generating the isoallelic mutant MGAS10870 (sclA Carrier ) was as described previously (15). Briefly, the sclA Carrier allele was amplified using the primers 2902F and 2487R from the carrier strain MGAS23440 and subsequently ligated into the temperature sensitive E. coli-Gram-positive shuttle vector pJL1055 using BamHI and XhoI (16) to generate pJSF41.…”

“…The resulting plasmids (see Table S1 in the supplemental material) were electroporated into MGAS10870⌬sclA to generate the individually transcomplemented strains. Isolation of bacterial proteins and Western immunoblot analysis were carried out as described previously (15).…”

NEPHRITOGENIC ACTIVITY OF STREPTOCOCCUS PYOGENES emm1 AND emm12 GENOTYPES ISOLATED FROM PATIENTS AND ASYMPTOMATIC CARRIERS

“…Если Fc-рецепторные белки для нативного IgG были описаны ранее [14,15], то на сегодня наука не располагает сведениями о белках, связыва-ющих IC. Недавно было показано [6], что штаммы СГА, выделяемые от асимптомных носителей инфекции, нередко несут делецию в промо-торной области гена Mga-регулятора. Есте-ственно, что такие штаммы-мутанты долж-ны быть дефектными по М-белкам, и в силу этого лишены способности связывать IC.…”