Staphylococcus aureus is a ubiquitous human pathogen capable of causing diverse diseases in part due to its ability to form a biofilm. The literature regarding regulators of S. aureus biofilm formation is inconsistent, employing varying strains and experimental conditions making results un-comparable. Therefore, we examined the relative impact of 23 mutations on biofilm formation in the USA300, methicillin-resistant strain LAC under consistent experimental conditions. Mutation of sarA, atl, codY, rsbU, and sigB limited, while mutation of fur and mgrA increased biofilm formation. Mutation of sarA, mgrA, and sigB had the same effects in the USA200 methicillin-sensitive strain UAMS-1, but mutation of codY increased rather than decreased biofilm formation. Examination of four additional clinical isolates suggests the differential impact of codY on biofilm formation may be a conserved characteristic of methicillin-resistant versus methicillin-sensitive strains. In vitro and in vivo antibiotic susceptibility assays were performed in both strains with daptomycin and ceftaroline. Mutation of sarA or sigB was comparable to each other and greater than any other mutation with significantly increased susceptibility to both antibiotics in both strains.
Finally, we demonstrate that mutation of xerC, which encodes a homologue of an Escherichia coli recombinase, limits biofilm formation and was correlated with increased antibiotic susceptibility in the context of an established biofilm in vivo in LAC and UAMS-1. Virulence in a murine bacteremia model was attenuated and correlated with decreased accumulation of alpha toxin and increased accumulation of protein A. xerC mutants also had reduced accumulation of RNAIII and AgrA implying decreased virulence in bacteremia, but not biofilm formation, may be mediated at least in part by agr. These results demonstrate that xerC contributes to biofilm-associated infections and acute bacteremia and this is likely due to agr-independent and dependent pathways, respectively.
The results reported in this dissertation demonstrate that mutation of sarA, sigB, and xerC are clinically relevant making these loci potential therapeutic targets. While more work is necessary to determine possible limitations and development of therapeutic inhibitors, this dissertation has laid a strong foundation in determining which regulatory loci previously implicated in biofilm formation would make the most efficacious targets.
|Advisor:||Smeltzer, Mark S.|
|Commitee:||Blevins, Jon S., Harik, Nada S., Lee, Chia Y., Tackett, Alan J.|
|School:||University of Arkansas for Medical Sciences|
|Department:||Interdisciplinary Biomedical Sciences|
|School Location:||United States -- Arkansas|
|Source:||DAI-B 78/12(E), Dissertation Abstracts International|
|Keywords:||Biofilm formation, Virulence regulation, sarA, xerC|
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