Scholar: Josette Medicielo
Major: Molecular Microbiology & Immunology
Faculty Mentors: Dr. Paul Sumby
Research Topic: Investigating the Association of Serotype M28 group A Streptococcus with Puerperal Sepsis
Abstract: Streptococcus pyogenes, also known as group A Streptococcus (GAS), is a Gram-positive bacterium known to cause numerous human diseases such as pharyngitis, impetigo, and puerperal sepsis (aka maternal childbed fever). All GAS express virulence factor protein M, the sequence of which is highly variable among isolates. This variability categorizes GAS isolates into different serotypes (e.g. M1, M2... M89 etc.). M28 GAS is non-randomly associated with puerperal sepsis infection. Its genome harbors "Region of Difference 2" (RD2), a 36.3 kb region specific to M28 that appears to have been acquired via horizontal gene transfer (HGT) from group B Streptococcus - a vaginal microflora component responsible for maternal postpartum invasive infections. To test the hypothesis that RD2 contributes to the association of M28 isolates with causing puerperal sepsis, we compared a parental M28 isolate with an RD2 deletion mutant derivative (strain M28ΔRD2). Using a cell-culture based adherence assay with human vaginal epithelial cells, the mutant's relative adherence was significantly lower than the parental strain. When complemented, the strain returned to levels commensurate with parental strain. Therefore, RD2 appears to enhance M28 GAS adhesion. The results of whole genome sequencing (WGS), performed to assay whether M28ΔRD2 contains unwanted mutations in addition to the RD2 deletion, indicated 28 putative single nucleotide polymorphisms (SNPs) between strains. To determine whether these SNPs are real, and subsequently whether they or the RD2 deletion are responsible for the observed phenotype, the putative SNPs must be amplified and sequenced in both strains. If SNPs are verified, these mutations will be fixed via allelic replacement. My work in the Sumby lab will include amplifying and sequencing these regions of DNA from GAS and performing bioinformatic comparisons of the sequences. Future research into M28 GAS and RD2 function include gain-of-function experiments to introduce RD2 to GAS serotypes that normally lack this region.
New Scholar: 2017 cohort