Browsing by Author "Lockhart, Joey Scott"

Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Biofilm-derived Small Molecules Released from Mixed-species Cultures of Fusobacterium necrophorum and Porphyromonas levii Inhibit Bovine Neutrophil Functional Responses
    (2022-05-06) Lockhart, Joey Scott; Morck, Douglas Walter; Buret, Andre G; Harrison, Joe Jonathan; Hirota, Simon; De Buck, Jeroen Marc Daniel; James, Garth Alan
    Bacterial biofilms are surface adhered communities of microorganisms encased in a protective polysaccharide layer. These resilient structures present significant challenges for effective host immune cell clearance or clinical interventions, frequently resulting in recurrent infections in cattle, humans, and other animals. Fusobacterium necrophorum and Porphyromonas levii are two species of anaerobic, Gram-negative, opportunistic pathogens that have been described as etiological agents in a variety of necrotic, recalcitrant infections. With antimicrobial resistance on the rise, it is important to elucidate the reasons why biofilm-associated infections are so difficult to eradicate. Neutrophils are critical first responder cells that are recruited to a site of bacterial colonization to initiate the inflammatory response. In this dissertation research, an in vitro system for the growth of mixed-species anaerobic biofilms was employed to investigate bovine neutrophil responses to biofilm bacteria compared to planktonic cultures of the same two species. Neutrophils exposed to biofilm soluble factors generated reduced oxidative and chemotactic responses compared to neutrophils exposed to planktonic bacteria-generated products. Ultra-filtration revealed that a <3kDa molecule is differentially expressed in the bacterial supernatants and allows biofilm-bacteria to inhibit neutrophil responses. Intensive heat, protease, lipase, or nuclease treatment of the <3kDa fractions prior to exposure to bovine neutrophils did not alter the differential oxidative responses. This led to an investigation of small, heat stable compounds and our results suggest that the accumulation of protoporphyrin IX in the biofilm mode of growth attenuates neutrophil chemotaxis and reactive oxygen species production. This work provides evidence for a mechanism by which these biofilm bacteria evade host immune cells and understanding such mechanisms is important to reduce the persistent inflammation and negative clinical outcomes associated with chronic biofilm-mediated disease.
  • Thumbnail Image
    ItemOpen Access
    Neutrophil Responses to Mixed-Species Anaerobic Biofilms
    (2015-01-28) Lockhart, Joey Scott; Morck, Douglas
    Biofilms composed of anaerobic bacteria often result in persistent infections and chronic inflammation. Host immune cells have difficulties in clearing biofilm-related infections and this can result in unnecessary tissue damage due to the overproduction of proinflammatory mediators. The objective of this project was to generate mixed-species anaerobic biofilms composed of two opportunistic pathogens, Fusobacterium necrophorum and Porphyromonas levii and measure neutrophil responses. Neutrophils are a vital component of the innate immune system and the results show that neutrophils exposed to mixed-species planktonic bacteria exhibit a more extensive oxidative response than neutrophils exposed to biofilms composed of the same bacteria. The limited neutrophil response to biofilm bacteria may explain the reduced ability of the innate immune system to eradicate biofilm-associated infections. The results demonstrate that bacterial lipopolysaccharide plays a significant role in the stimulation of neutrophils, however the evidence points to the presence of other stimulatory molecules in the bacterial media.