Enterococcus
Enterococcus By Richard Guilford Enterococcus 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 ithstand 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 to infect.
E. faecalis has been frequently found in root canal-treated teeth in prevalence values ranging from 30% to 90% of the cases. Root canal-treated teeth are about nine times more likely to have E. faecalis than cases of primary infections. Enterococcus faecium is an alpha hemolitic or nonhemolitic, bacterium. It is used as a probiotic in animals. It can be commensal (a harmlessly coexisting organism) in the human intestine, but it may also be pathogenic, causing diseases such as neonatal meningitis.
Enterococcal meningitis is also a rare complication of neurosurgery. It often requires treatment with IV or intrathecal (something introduced into or occurring in the space under the arachnoid membrane of the brain or spinal cord) vancomycin, yet it is uncertain whether its use has any impact on outcome. The removal of any neurological devices is an important part of the management of these infections. Enterococcus solitarius and Enterococcus gallinarum are two more species of enterococcus.
The genus Enterococcus includes more than 17 species, but only a few cause clinical infections in humans. Infection control programs were created three decades ago to control antibiotic-resistant nosocomial infections, but there has been little evidence of control in most facilities. After long, steady increases of MRSA and VRE infections in hospitals, the Society for Healthcare Epidemiology of America (SHEA) Board of Directors made reducing antibiotic-resistant infections a strategic SHEA goal in January 2000.
After 2 more years without improvement, a SHEA task force was appointed to draft an evidence-based guideline on preventing nosocomial transmission of pathogens, focusing on the two considered most out of control: MRSA and VRE. Medline searches were conducted pning 1966 to 2002. Many interpretations of unpublished studies providing sufficient data were included. Frequent antibiotics in healthcare settings provided a small advantage for resistant strands, but patients with MRSA or VRE usually acquire it through spread. The CDC has long-recommended contact precautions for patients colonized or infected with these pathogens.
Most facilities have required this as policy, but have not actively identified infected patients with surveillance cultures (lab tests performed to determine possible abnormalities or infection) and tests, leaving most infected patients undetected and not isolated. Many studies have shown control of endemic (exclusively native to a place) and/or epidemic (everywhere) MRSA and VRE infections using surveillance cultures and contact precautions. Active surveillance cultures are essential to identify the infected to prevent spread of MRSA and VRE infections and make control possible using the CDC’s long-recommended contact precautions.
Testing for enterococci can be tricky. Enterococci have been recognized to be of fecal origin since the beginning of this century. The usual ecological home for the Enterococcus species is the intestines of humans and other animals. However, enterococci are ubiquitous (present everywhere) and can be found free-living in soil, on plants, or in dairy products. Enterococcus comprises gram-positive cocci that are catalase (a common enzyme found in nearly all living organisms that are exposed to oxygen, where it functions to catalyze the decomposition of hydrogen peroxide to water and oxygen) negative, usually facultative anaerobic acteria. There is clear evidence of the genotypic (concerning the genetic makeup) identity of Enterococcus, based on molecular studies. Enterococci have also been related to human diseases, becoming established as major nosocomial pathogens. The isolation of strains resistant to many antibiotics has become important in public health concerns. In addition, Enterococcus and Streptococcus have been proposed as indicators of fecal contamination in water because of their high abundance in feces and their long survival in the environment.
Although the ratio of fecal coliforms to fecal streptococci has been ruled out as an indicator, the identi? cation of species associated with a given environment or host might provide additional information about the origin and the source of fecal contamination. The ability of enterococci to grow under particular conditions is widely used in their selective identification. This characteristic allows the detection and enumeration of enterococci with a selective medium (template used to grow bacteria) M-enterococcus agar or KF streptococcus agar, and by using bile-esculin-azide agar (another medium) as a further test for con? mation. Although this approach can distinguish Enterococci from other bacterial species, some may be identi? ed wrongly. The use of these media can hurt either selectivity (choices of bacteria found) or productivity (ability for bacteria to grow). Even though this approach was to identify enterococci species, it is unsuitable for the detection of certain enterococci species because they do not grow on these media. In addition, other bacterial species such as Streptococcus are able to grow on the media, presenting results similar to those of Enterococci.
Enterococci are diverse and enigmatic. There are many strains and many complications that can arise from them. They are both harmless and deadly, useful and destructive. They can be used to aid digestion, or feared in a hospital setting. They are indeed a medical paradox. With continued study, we hope to learn from and understand these bacteria if not to aid us in our expansion of knowledge, then to rid us of a potentially critical threat in our hospital settings. Gilmore MS, (2002). The Enterococci: Pathogenesis, Molecular Biology, and Antibiotic Resistance.
Fisher K, Phillips C (June 2009). “The ecology, epidemiology and virulence of Enterococcus”. Jin G, Jeng HW, Bradford H, Englande AJ (2004). “Comparison of E. coli, enterococci, and fecal coliform as indicators for brackish water quality assessment”. Carlene A. Muto, MD, MS; John A. Jernigan, MD, MS; Belinda E. Ostrowsky, MD, MPH; Herve M. Richet, MD; William R. Jarvis, MD; John M. Boyce, MD; Barry M. Farr, MD, MSc (May 2003). “SHEA Guideline for Preventing Nosocomial Transmission of Multidrug-Resistant Strains of Staphylococcus aureus and Enterococcus”
