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INVESTIGATOR: Richards, V.

PERFORMING INSTITUTION:
CLEMSON UNIVERSITY
CLEMSON, SOUTH CAROLINA 29634

POPULATION GENOMICS OF STREPTOCOCCUS AGALACTIAE FROM INFECTED BOVINE AND FISH SOURCES

NON-TECHNICAL SUMMARY: Streptococccus agalactiae (group B Streptococcus - GBS) is a member of the commensal microbiota of the intestinal and genitourinary tracts of humans, but is also a leading cause of morbidity and mortality in newborn babies, pregnant women, and the elderly [1]. The other major reservoir for the bacterium is bovine, where it has long been recognized as a common cause of mastitis, a major production limiting disease in developed and developing countries around the world. S. agalactiae has also been identified as an aetiological agent of septicaemia and meningo-encephalitis in saltwater and freshwater fish species, and is now considered an important threat to the aquaculture industry [2-4]. Although there is considerable evidence for host- adaptation among strains of S. agalactiae, there is potential for foodborne and human-to-animal or animal-to-human transmission of the pathogen [5-7]. In addition to anthroponotic or zoonotic transmission, the possibility of emergence of human- pathogenic clones from an animal reservoir has been raised [8], as well as the suggestion that re-emergence of the pathogen in animal populations may be due to spill-over or adaptation of strains from humans [9]. There is therefore, a clear need for a better understanding of the evolution and transmission dynamics of S. agalactiae both within and across host species, including humans, agricultural, and aquaculture species.We take advantage of the rapidly decreasing cost of next-generation genome sequencing technology to examine for the first time the population genetic structure and dynamics of S. agalactiae on a global scale involving different hosts and disease states. This study will provide valuable insight on the population structure and diversity of S. agalactiae, uncover emergent clones, and identify associations between specific lineages and isolation source. Comparative genomics of multiple isolates derived from diseased bovine and fish sources, compared to human sourced isolates, should (i) identify genes that are key to host adaptation and possibly linked to the cause of disease, and (ii) allow estimation of the direction and rate of bacteria migration among populations and therefore provide insight into transmission dynamics among hosts.This project is directly related to the Foundational Program's priority area of "Animal Health and Production" and the challenge area of "Keeping American agriculture competitive" by identifying genes linked to bovine mastitis and fish septicaemia, caused by S. agalactiae. It will also provide data on transmission dynamics between these sources of infection and is therefore also linked to the challenge area of "Improving food safety." Collectively, the information arising from this project could ultimately lead to more effective preventative and treatment programs. Findings will be disseminated via scientific conferences and peer reviewed publications.

OBJECTIVES: 1. Describe the Streptococcus agalactiae population structure, genetic diversity, migration patterns, and demographic history using genome wide single nucleotide polymorphism (SNP) data in a global strain collection from humans, bovines, and fish, identifying associations between phylogenetic lineages and isolation source.2. Determination of the core genome, unique core genes, and dispensable genome components of distinct S. agalactiae lineages, as determined by genome wide SNP genotyping, characteristic of different host species and disease states.