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2021 OMIG Abstract
Genome Analysis of Viridans Group Streptococcus Strains from Endophthalmitis
Mary E. Marquart1, Kurtis C. Showmaker2, K. Taylor Hellmann1, Mary A. Carr1, K. Michael Lovell1,
Brigitte E. Martin3, D. Ashley Robinson1
Departments of 1Microbiology and Immunology, 2Data Science, and 3Pharmacology and Toxicology, University of Mississippi Medical Center, Jackson, Mississippi
Purpose: Poor visual outcomes often result from endophthalmitis caused by Viridans streptococci, yet little is known regarding the virulence mechanisms of these bacteria. The purpose of this study was to determine core genes shared by this group that can be selected for future research on potential common modes of pathogenesis.
Methods: Whole genome paired end sequencing was conducted on the Illumina NextSeq500 platform for 21 endophthalmitis isolates. Raw reads were trimmed with Trimmomatic and assembled with SPAdes. Pan-genomic analysis including the identification of the core genome was conducted with the Roary pipeline (https://sanger-pathogens.github.io/Roary/). Gene prediction and annotation was conducted with the NCBI Prokaryotic Genome Annotation Pipeline (PGAP).
Results: The 21 genomes matched to reference genomes of 8 different species: S. constellatus, S. gordonii, S. mitis, S. mutans, S. oralis, S. parasanguinis, S. salivarius, and S. vestibularis. Genome assemblies had sizes in the range of 1.8 – 2.3 Mbp. Each genome was predicted to encode approximately 2,000 genes with a total of 12,667 genes identified across all 21 strains. Most of the common genes were those involved in transcription, translation, and cellular metabolism and/or transport. The S. mitis and S. oralis strains (15 of the 21 strains; 71%), which cluster more closely together in the Mitis clade, shared 1,139 genes from a total of 6,051. Additional transcriptional regulator and cellular metabolism/transport genes, as well as genes encoding pilus assembly subunits, hemolysins, penicillin-binding proteins, fibronectin-binding proteins, and proteases, were identified in the S. mitis/S. oralis group.
Conclusions: The endophthalmitis strains of Viridans streptococci are genetically diverse, sharing a core genome of less than 15% of the total number of genes for each strain. Restricting the analysis to the dominant species S. mitis and S. oralis, which led to a core genome of over 50%, revealed genes encoding putative virulence factors. Whether streptococcal endophthalmitis severity is due to bacterial overgrowth and inflammatory bystander damage alone, or also involves putative bacterial virulence factors that enhance pathogenesis, is yet to be determined.
Disclosure: S
Support: NIH grant R21EY028325
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