Abstract
Enterococcus faecalis is a significant threat in the nosocomial setting due to the emergence of isolates that are multi-antibiotic resistant, refractory to the available therapies and equipped with a variety of pathogenicity determinants. This bacterium uses quorum-sensing systems to regulate its physiological processes, including the expression of virulence traits, to adapt and proliferate within a host. Here, we describe the construction and application of two bioluminescence-based reporter systems for the direct detection of the quorum-sensing regulated expression of (i) the gelatinase biosynthesis-activating pheromone (GBAP) and (ii) the cytolysin small subunit (CylLS) in natural samples. The two E. faecalis reporters conditionally expressed bioluminescence in the presence of GBAP and CylLS both in the supernatants of liquid cultures and in an agar-overlay assay in as little as three hours, with a high level of sensitivity. Biosensors employed to investigate the interaction between the fsr and cyl systems revealed that fsr impeded CylLS activity by 75%. Furthermore, we identified a clinical E. faecalis isolate that acted as a biological cheater, producing cytolysin only upon sensing CylLS-producers in its environment. This isolate enhanced its virulence during polymicrobial systemic infection of Galleria mellonella.
Highlights
Bioluminescence based biosensors for quantitative detection of enterococcal peptide–pheromone activity reveal inter-strain telesensing in vivo during polymicrobial systemic infection
We identified a clinical E. faecalis isolate that acted as a biological cheater, producing cytolysin only upon sensing cytolysin small subunit (CylLS)-producers in its environment
Three prominent peptide pheromone systems associated with highly virulent strains of E. faecalis are involved in environmentally regulated telesensing systems, including a conjugative system mediated by pheromone-responsive plasmids, the Fsr regulatory system, and cytolysin signalling[13–15]
Summary
Bioluminescence based biosensors for quantitative detection of enterococcal peptide–pheromone activity reveal inter-strain telesensing in vivo during polymicrobial systemic infection. Enterococcus faecalis is a significant threat in the nosocomial setting due to the emergence of isolates that are multi-antibiotic resistant, refractory to the available therapies and equipped with a variety of pathogenicity determinants This bacterium uses quorum-sensing systems to regulate its physiological processes, including the expression of virulence traits, to adapt and proliferate within a host. Concentration or physiochemical changes in those ‘probes’ are perceived as discharging environmental signals, allowing the bacteria to trigger an appropriate response in the host Responses, such as enhancing their fitness for the colonisation of an environmental niche via subversion of the host’s immune responses, releasing virulence factors as a defensive mechanism against competitive microorganisms or eukaryotic cells, differentiating into certain morphological forms in hostile environments and regulating genetic exchange, are coordinated through the telesensing systems[1,2]. E. faecalis can finely tune the expression of cyl genes according to the presence of target cells
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