Graduation Year

2024

Document Type

Thesis

Degree

M.S.P.H.

Degree Name

MS in Public Health (M.S.P.H.)

Degree Granting Department

Public Health

Major Professor

John Adams, Ph.D.

Committee Member

Lindsey Shaw, Ph.D.

Committee Member

Sophie Darch, Ph.D.

Keywords

MRSA, S. aureus, biofilm, cytotoxicity, protease, hemolysin

Abstract

Staphylococcus aureus is a human pathogen of serious concern because of its ability to cause serious and wide-ranging disease. Of particular concern is the ability of S. aureus to cause bacteremia (SAB), allowing the bacteria to disseminate and spread to various organs. This study addressed this issue through the phenotypic characterization of two methicillin-resistant S. aureus (MRSA) clinical isolates taken from patients with sustained complicated bacteremia at Tampa General Hospital, referred to as SA1097 and SA1098. A battery of phenotypic tests was conducted on these strains, including a growth curve, hemolysis and proteolysis screenings, cytotoxicity assays using human neutrophils, blood survival assays in human blood, and biofilm formation assays. These isolates both exhibited unique phenotypes that differed from a control USA300 strain, Lac. Both isolates exhibited diminished hemolysis and proteolysis compared to Lac. Despite these phenotypes, both SA1097 and SA1098 showed levels of cytotoxicity consistent with Lac. Interestingly, despite the high levels of cytotoxicity observed, the isolates survived poorly in blood compared to Lac, with SA1098’s slight advantage over SA1097 likely attributable to its increased proteolytic activity. The proteolytic phenotypes observed also influenced the clinical isolates in their strong proclivity for biofilm formation. The observations in this study provide valuable insight into the varying and shared phenotypes among clinical MRSA isolates isolated from bacteremia patients. This information may contribute to knowledge on the contribution of virulence factors to phenotypes in MRSA strains, as well as inform prevention and treatment efforts for S. aureus strains circulating in the community.

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