Basal levels of (p)ppGpp differentially affect the pathogenesis of infective endocarditis in Enterococcus faecalis

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• The alarmone guanosine tetraphosphate (ppGpp) is key to bacterial virulence and the stringent response.
• Previous work showed varying cellular ppGpp levels impact Enterococcus faecalis abscess persistence.
• The role of ppGpp in infective endocarditis (IE), a heart valve biofilm infection, was unexplored.

Purpose of the Study:

• To investigate the contribution of ppGpp to Enterococcus faecalis infective endocarditis (IE) pathogenesis.
• To determine if the stringent response is activated in IE and how basal ppGpp levels affect IE-associated processes.

Main Methods:

• Generated Enterococcus faecalis mutants with altered ppGpp levels (Δrel, ΔrelΔrelQ).
• Assessed valve colonization in a rabbit IE model.
• Evaluated bacterial surface binding to various matrices and ex vivo heart valves.
• Measured extracellular gelatinase activity and endothelial cell invasion.

Main Results:

• The stringent response was not activated in heart valve E. faecalis.
• Deletion of the Rel gene (Δrel) significantly impaired valve colonization, indicating ppGpp regulation is critical.
• The Δrel mutant showed no defect in surface or valve attachment but had impaired invasion of endothelial cells.
• Extracellular gelatinase activity was unaffected by ppGpp levels.

Conclusions:

• ppGpp itself is dispensable for E. faecalis IE, but regulating its levels is vital for valve colonization.
• Basal ppGpp levels, rather than the stringent response, differentially impact IE pathogenesis, particularly bacterial invasion.
• This study highlights the distinct roles of ppGpp regulation versus stringent response activation in bacterial virulence.