Graduation Date

Spring 5-6-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Immunology, Pathology & Infectious Disease

First Advisor

Tammy Kielian

Abstract

Staphylococcus aureus (S. aureus) is a versatile pathogen that can occupy a wide range of niches within the human body, including implanted medical devices such as in prosthetic joint infection (PJI). S. aureus adheres to these medical devices and forms a biofilm, which is a community of bacteria contained within an extracellular matrix that leads to gradients in nutrient and oxygen availability. During PJI, the biofilm is recalcitrant to antibiotics and immune-mediated clearance, leading to treatment failure, mortality, and a high healthcare burden. This is partially due to skewing of the host immune system to an anti-inflammatory state, highlighted by the abundance of granulocytic myeloid-derived suppressor cells (G-MDSCs) and production of IL-10 at the site of infection, which inhibit the bactericidal activity of other immune cells. In these studies, we demonstrate that S. aureus biofilms lacking functional ATP synthase (∆atpA) or the ability to generate the fermentative metabolite formate (∆pflB) had altered biofilm structure. These metabolic alterations to S. aureus also led to a heightened pro-inflammatory immune response and enhanced bacterial clearance in vivo in a mouse PJI model. Recent evidence has also demonstrated that S. aureus can survive and replicate within macrophages. We showed that S. aureus survival within human monocyte-derived macrophages (HMDMs) led to macrophage lysis, serving as a nucleation point for biofilm development. This study also revealed donor-dependent variability in HMDM metabolism, which may affect S. aureus survival. Finally, we explored the fate of G-MDSCs during PJI where a small population of these cells acquire F4/80 and MHC class II, while retaining immunosuppressive properties. We then used cellular indexing of transcriptomes by sequencing (CITE-seq) to analyze the transcriptional profile of the F4/80+MHC class II+ MDSC population, which revealed increased production of tumor necrosis factor and transcriptional attributes of MDSCs, macrophages, and neutrophils. F4/80+MHCII+ MDSCs also exhibited increased mitochondrial gene expression compared to G-MDSCs and neutrophils, suggesting they may be more closely related to M-MDSCs. Collectively, these studies demonstrate the deep connection between metabolism and function of both leukocytes and S. aureus during PJI.

Comments

2023 Copyright, the authors

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