2.2.5. Enterococcus

Cross-kingdom pathogenesis is not limited to Gram-negative bacteria. Enterococci are part of the normal intestinal flora of humans and animals, but are also important pathogens responsible for serious infections, especially in immunocompromised patients. With increasing antibiotic resistance, enterococci are recognized as nosocomial pathogens that can be challenging to treat. The genus Enterococcus includes more than 17 species, but only a few can cause local or systemic clinical infections, including urinary tract and abdominal infections, wound infections, bacteremia, and endocarditis. Clinical isolates of E. faecalis have been found to produce hemolysin—a virulence factor that leads to the lysis of red blood cells. Hemolytic strains exhibit multiple drug resistance more frequently than non-hemolytic strains, whereas strains isolated from fecal specimens of healthy individuals display a low (17%) incidence of hemolysin production. E. faecalis is not only capable of infecting mammalian and nematode hosts, but also the plant Arabidopsis thaliana, causing plant death seven days after inoculation under laboratory conditions. The manifestation of disease initially begins once the bacterium has successfully attached itself to the leaf surface, where upon entry into the leaf tissue through the stomata or wounds, E. faecalis multiplies and colonizes the intercellular spaces of the plant host and causes rotting and disruption of the plant cell wall and membrane structures. The phytopathogenicity of E. faecalis appears to involve some of the same genetic determinants involved in animal pathogenesis, including the quorum-sensing system gene and a serine protease. E. faecalis clearly uses a general disease strategy that allows it to use the same virulence factors for exploiting two different hosts.