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Non-clinical isolates bring new findings on enterococcal virulence
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Enterococci are Gram-positive lactic acid bacteria, widespread in
the environment, present in water, soil, plants and animals, including
humans. They typically colonize the skin and mucous membranes, namely
the gastrointestinal tract. However, enterococci, and most notably
Enterococcus faecalis and Enterococcus faecium, have become
problematic causative agents of several nosocomial infections, including
urinary tract infections, bacteraemia, surgical sight infections, and
endocarditis. Besides being opportunistic pathogens, the resilient bacteria
of the genus Enterococcus are key factors contributing to the ripening,
flavour, and the organoleptic properties of fermented food products.
The ubiquitous nature of enterococci derives from a number of
features, which can be intrinsic to the genus or specific to some species or
even strains. These traits allow probing the environment in order to adapt,
enabling a survival and fitness advantage. They are encoded in numerous
genes that can be easily transferable due to the high genomic promiscuity
of enterococci. These genes have been ascribed a role in virulence as they
are relevant to different stages of the bacterial infection process, including adhesion, colonization, invasion, evasion of the immune system and spread
through the hostʼs tissues. Enterococcal virulence factors can be either
secreted (cytolysin, proteases, hyaluronidase, superoxide), surface
associated (enterococcal surface protein, aggregation substance,
extracellular polymeric substances, pilin gene clusters, enterococcal
microbial surface component recognizing adhesive matrix molecules), or
intracellular. At the time this thesis work began, researchers were starting
to realize that virulence factors in enterococcal clinical isolates were also
present in isolates from other environments, in particular, where
enterococci play beneficial roles, namely food. Since dissemination of
virulence factors among food isolates was no longer crucial, other issues
started to become relevant in the still debated enterococcal virulence.(...)
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Dissertation presented to obtain the PhD degree in Biology
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Universidade Nova de Lisboa. Instituto de Tecnologia Química e Biológica