The Streptococcus Anginosus Group (SAG) is a group of Gram-positive cocci
which require carbon dioxide to grow. They are commensal members of the
healthy upper respiratory, gastrointestinal and female urogenital tract; however,
they are most commonly known as major pathogens in brain and liver abscesses,
forming both mono- and polymicrobial infections. The Streptococcus invasion
locus (sil), first identified as a virulence factor in Group A Streptococcus (GAS),
has recently been identified in the SAG. The sil locus in GAS is a two component
quorum-sensing system composed of three operons: silAB, coding for a two
component system; silE/D/CR, coding for an ABC transporter and a signal
peptide, and silC, which overlaps silCR on the opposite strand. The presence of
exogenous SilCR activates SilA, which in turn upregulates the transcription of the
silE/D/CR operon. In the SAG, however, silCR and silED have distinct promoters,
and the SAG sil system lacks the silC gene. In this study, I examined the
transcriptional dynamics of the sil system in S. intermedius B196. I determined
that SilA is the major regulator of the genes in the sil system, being one of the
first genes of the system to be expressed, and likely upregulates its own
transcription. I also found evidence suggesting that, despite having its own
promoter, silCR transcription may still be driven by the silED promoter. I also
found evidence that suggests silED may be responsible for the export and/or
processing of bacteriocins targeting closely related species or strains. / Thesis / Master of Science (MSc) / The Streptococcus are a group of bacteria known for causing diseases
ranging from strep throat to flesh-eating disease; however, many species of
Streptococcus are usually non-pathogenic, and live in our bodies without causing
harm. One group of these bacteria, the Streptococcus Anginosus Group (SAG), is
commonly found in our mouths and gut and usually cause no harm; however, in
some cases it can cause infections. How these organisms switch from being nonpathogenic
to pathogenic is unknown, but recently a gene network that appears
to play a role in infection, the Streptococcus invasion locus (sil), was identified in
the SAG. This gene network senses the signals released by other bacteria with
the network, and only turns on when enough signal is present. The goal of this
study is to examine how the system works in the SAG in order to determine how
these bacteria coordinate sil gene expression.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/23741 |
| Date | January 2018 |
| Creators | Wu, Bryan |
| Contributors | Surette, Michael, Biochemistry and Biomedical Sciences |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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