Enterococcal Pathogenesis

Enterococcusfaecalis is a gram-positive coccus, has a low G+C content (37.5%), and is a facultative anaerobe that grows optimally at 35 °C (with a growth range of 1045 °C). E.faecalis forms part of the normal host microflora of both the human and animal intestinal tracts and can also be isolated from insects such as cockroaches, flies, and beetles [1]. In humans typical concentrations of enterococci in stool are up to 108 CFU per gram [2], and because of this they are also abundant in waste-water, sewage, on vegetation, and in other environment areas where contamination has occurred. Although E.faecalis is a normal member of the human gastrointestinal tract, problems occur when this organism gains access to sites it does not normally colonize.

Since 1986, enterococci have consistently ranked among the most common pathogens isolated from nosocomial infections [3]. Enterococci are associated with a variety of clinical infections, the most common being urinary tract infections.

Urinary tract infections caused by enterococci are generally acquired in a long-term health care facility, and because of the bacteria's increased exposure to antimicrobial agents in such environments, are also more likely to be resistant to some antimicrobial agents. In the 2000 SENTRY surveillance program enterococci were the second ranked cause of nosocomial urinary tract infections, accounting for 12.6% of all infections [4]. The second most frequent infections caused by enterococci are intra-abdominal abscesses and postsurgical wound infections, and these are followed in frequency by bloodstream infections (bacteremia) and bacterial endocarditis. According to National Nosocomial Infections Surveillance (NNIS) data from January 1992 to July 1998, enterococci ranked first as the causative agent in surgical site infection and third in bloodstream infections among patients in intensive care units [5]. At a much lower frequency, enterococci can be involved in central nervous system and neonatal infections, and very rarely can be involved in osteomyelitis, respiratory tract infections, and cellulitis. E.faecalis is the most prevalent enterococcal species associated with human infections. Data from the SENTRY surveillance program (1997-1999) showed that during this time period, E.faecalis accounted for 57.2-76.8% of enterococcal nosocomial infections, while Enterococcus faecium made up 4.6% to 20% [6].

To cause disease, bacterial pathogens need to be able to adapt to the physiological conditions found within the host. A potential reason for the emergence of E. faecalis as a causative agent of nosocomial infection is the robust nature of this organism. E. faecalis has an intrinsic ability to grow in hypotonic, hypertonic, acidic, or alkaline conditions and to withstand detergents, oxidative stress, and desiccation. To discover more about the mechanisms this bacteria uses both to survive and to cause infection in the clinical setting, the genome of the first reported clinical vancomycin-resistant E.faecalis isolate in the United States, E.faecalis V583 [7], was sequenced [8].

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