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By Richard Guilford

Enterococcus, or more appropriately enterococci, are a family of bacteria in the division firmicutes (meaning strong skin and referring to the cell wall) and the class bacilli (which refers to its rod like shape). They look just like streptococcus bacteria from physical characteristics alone. In fact, members of the genus Enterococcus were classified as Group D Streptococcus until 1984 when genomic DNA analysis showed that a separate genus classification would be appropriate. Enterococci are part of the normal intestinal flora (good bacteria) of humans and animals but are also important pathogens responsible for serious infections. They are considered gram-positive, meaning they stain dark blue or violet. They also mostly occur in pairs or short chains. Enterococci are facultative anaerobic organisms, meaning they can thrive in both oxygen rich and oxygen poor environments. They do not form spores as many bacteria do, meaning they do not have a reproductive structure that is adapted for dispersal and survival for extended periods of time in unfavorable conditions. Nevertheless, they are tolerant of a wide range of environmental conditions: such as extreme temperature (10-45°C), pH (4.5-10.0) and high sodium chloride concentration. In bodies of water, the acceptable level of contamination is very low, for example in the state of Hawaii, with among the strictest tolerances in the United States, the limit for water off its beaches is 7 colony-forming units per 100 ml of water. Anything above that, the state may post warnings to stay out of the ocean. In 2004, Enterococcus spp. took the place of fecal coliform as the new federal standard for water quality at public beaches. It is believed to provide a higher correlation than fecal coliform with many of the human pathogens often found in city sewage (eww right?). There are many strains of enterococcus. Important clinical infections caused by Enterococcus include urinary tract infections, bacteremia, bacterial endocarditis, diverticulitis, and meningitis. Sensitive strains of these bacteria can be treated with ampicillin and vancomycin, two well known and often used antibiotics. An important feature of enterococcus is the high level of intrinsic antibiotic resistance, meaning its inherent ability to withstand some of the more common antibiotics. Some enterococci are intrinsically resistant to beta-lactam-based antibiotics (those include some penicillins and virtually all cephalosporins) as well as many aminoglycosides (an amino-sugar that can sometimes function as an antibiotic). In the last two decades, particularly virulent strains of enterococcus that are resistant to vancomycin (vancomycin-resistant Enterococcus, or VRE) have emerged in nosocomial (infections caught in hospitals while care is being given) infections of hospitalized patients especially in the US. Other developed countries such as the UK have been spared this epidemic, and, in 2005, Singapore managed to halt an epidemic of VRE. VRE may be treated with quinupristin/dalfopristin (a special antibiotic developed to fight VRE) or Synercid with response rates of approximately 70%. Enterococcus avium is a species that is most commonly found in birds. Rarely, it is also a cause of infection in humans, and in such cases, may be vancomycin-reistant. It is referred to as VREA. VREA cases in humans have been successfully treated with linezolid (a synthetic antibiotic). Enterococcus durans and enterococcus faecalis are very similar. They are often mistaken for one another in determining infections. They inhabit the gastrointestinal tracts of humans and other mammals. It is among the main parts of some probiotic food supplements. Like other species in the genus enterococcus, E. faecalis can cause life-threatening infections in humans, especially in the nosocomial environment. The naturally high levels of antibiotic resistance found in E. faecalis contribute to its ability...
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