Enterococcus is a large genus of lactic acid bacteria of the phylum Bacillota. Enterococci are gram-positive cocci that often occur in pairs (diplococci) or short chains, and are difficult to distinguish from streptococci on physical characteristics alone. [2] Two species are common commensal organisms in the intestines of humans: E. faecalis (90–95%) and E. faecium (5–10%). Rare clusters of infections occur with other species, including E. casseliflavus, E. gallinarum , and E. raffinosus. [2]
Enterococci are facultative anaerobic organisms, i.e., they are capable of cellular respiration in both oxygen-rich and oxygen-poor environments. [3] Though they are not capable of forming spores, enterococci are tolerant of a wide range of environmental conditions: extreme temperature (10–45 °C), pH (4.6–9.9), and high sodium chloride concentrations. [4]
Enterococci exhibit variable hemolysis on blood agar. Differences occur between species, and between strains of species. More virulent organisms are more likely to exhibit alpha (partial) or beta (complete) hemolysis than less virulent specimens of Enterococcus, which frequently exhibit gamma (absent) hemolysis. [5]
Members of the genus Enterococcus (from Greek έντερο, éntero 'intestine' and κοκκος, coccos 'granule') were classified as group D Streptococcus until 1984, when genomic DNA analysis indicated a separate genus classification would be appropriate. [6]
This genus appears to have evolved 425 million years ago to 500 million years ago. [7]
Important clinical infections caused by Enterococcus include urinary tract infections (see Enterococcus faecalis ), bacteremia, bacterial endocarditis, diverticulitis, meningitis, and spontaneous bacterial peritonitis. [4] [8] [9] Sensitive strains of these bacteria can be treated with ampicillin, penicillin and vancomycin. [10] Urinary tract infections can be treated specifically with nitrofurantoin, even in cases of vancomycin resistance. [11]
Enterococcal meningitis is a rare complication of neurosurgery. It often requires treatment with intravenous or intrathecal vancomycin, yet it is debatable as to whether its use has any impact on outcome: the removal of any neurological devices is a crucial part of the management of these infections. [12] New epidemiological evidence has shown that enterococci are major infectious agent in chronic bacterial prostatitis. [13] Enterococci are able to form biofilm in the prostate gland, making their eradication difficult.[ citation needed ] Cases of enterococcal meningitis, in the absence of trauma or surgery, should raise suspicion of an underlying intestinal pathology (e.g., strongyloidiasis). [14]
From a medical standpoint, an important feature of this genus is the high level of intrinsic antibiotic resistance. Some enterococci are intrinsically resistant to β-lactam-based antibiotics (penicillins, cephalosporins, carbapenems), as well as many aminoglycosides. [8] 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 of hospitalized patients, especially in the US. [4] Other developed countries, such as the UK, have been spared this epidemic, and, in 2005, Singapore managed to halt an epidemic of VRE. [15] Although quinupristin/dalfopristin (Synercid) was previously indicated for treatment of VRE in the USA, the FDA approval for this indication has since been retracted. [16] The rationale for the retraction of Synercid's indication for VRE was based upon poor efficacy in E. faecalis, which is implicated in the vast majority of VRE cases. [17] [18] Tigecycline has also been shown to have antienterococcal activity, as has rifampicin. [19]
Bacillus haynesii CD223 and Advenella mimigardefordensis SM421 can inhibit the growth of Enterococcus spp. [20]
In bodies of water, the acceptable level of contamination is very low; for example in the state of Hawaii, and most of the United States, the limit for water off its beaches is a five-week geometric mean of 35 colony-forming units per 100 ml of water, above which the state may post warnings to stay out of the ocean. [21] In 2004, measurement of enterococci took the place of fecal coliforms as the new American federal standard for water quality at public saltwater beaches and alongside Escherichia coli at freshwater beaches. [22] It is believed to provide a higher correlation than fecal coliform with many of the human pathogens often found in city sewage. [23]
Streptococcus is a genus of gram-positive coccus or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales, in the phylum Bacillota. Cell division in streptococci occurs along a single axis, so as they grow, they tend to form pairs or chains that may appear bent or twisted. This differs from staphylococci, which divide along multiple axes, thereby generating irregular, grape-like clusters of cells. Most streptococci are oxidase-negative and catalase-negative, and many are facultative anaerobes.
Vancomycin is a glycopeptide antibiotic medication used to treat a number of bacterial infections. It is used intravenously as a treatment for complicated skin infections, bloodstream infections, endocarditis, bone and joint infections, and meningitis caused by methicillin-resistant Staphylococcus aureus. Blood levels may be measured to determine the correct dose. Vancomycin is also taken orally as a treatment for severe Clostridium difficile colitis. When taken orally it is poorly absorbed.
Bloodstream infections (BSIs) are infections of blood caused by blood-borne pathogens. Blood is normally a sterile environment, so the detection of microbes in the blood is always abnormal. A bloodstream infection is different from sepsis, which is characterized by severe inflammatory or immune responses of the host organism to pathogens.
Linezolid is an antibiotic used for the treatment of infections caused by Gram-positive bacteria that are resistant to other antibiotics. Linezolid is active against most Gram-positive bacteria that cause disease, including streptococci, vancomycin-resistant enterococci (VRE), and methicillin-resistant Staphylococcus aureus (MRSA). The main uses are infections of the skin and pneumonia although it may be used for a variety of other infections including drug-resistant tuberculosis. It is used either by injection into a vein or by mouth.
Vancomycin-resistant Staphylococcus aureus (VRSA) are strains of Staphylococcus aureus that have acquired resistance to the glycopeptide antibiotic vancomycin. Bacteria can acquire resistant genes either by random mutation or through the transfer of DNA from one bacterium to another. Resistance genes interfere with the normal antibiotic function and allow a bacteria to grow in the presence of the antibiotic. Resistance in VRSA is conferred by the plasmid-mediated vanA gene and operon. Although VRSA infections are uncommon, VRSA is often resistant to other types of antibiotics and a potential threat to public health because treatment options are limited. VRSA is resistant to many of the standard drugs used to treat S. aureus infections. Furthermore, resistance can be transferred from one bacterium to another.
Multiple drug resistance (MDR), multidrug resistance or multiresistance is antimicrobial resistance shown by a species of microorganism to at least one antimicrobial drug in three or more antimicrobial categories. Antimicrobial categories are classifications of antimicrobial agents based on their mode of action and specific to target organisms. The MDR types most threatening to public health are MDR bacteria that resist multiple antibiotics; other types include MDR viruses, parasites.
Quinupristin/dalfopristin, or quinupristin-dalfopristin, is a combination of two antibiotics used to treat infections by staphylococci and by vancomycin-resistant Enterococcus faecium.
Tigecycline, sold under the brand name Tygacil, is a tetracycline antibiotic medication for a number of bacterial infections. It is a glycylcycline administered intravenously. It was developed in response to the growing rate of antibiotic resistant bacteria such as Staphylococcus aureus, Acinetobacter baumannii, and E. coli. As a tetracycline derivative antibiotic, its structural modifications has expanded its therapeutic activity to include Gram-positive and Gram-negative organisms, including those of multi-drug resistance.
Vancomycin-resistant Enterococcus, or vancomycin-resistant enterococci (VRE), are bacterial strains of the genus Enterococcus that are resistant to the antibiotic vancomycin.
Enterococcus faecalis – formerly classified as part of the group D Streptococcus system – is a Gram-positive, commensal bacterium inhabiting the gastrointestinal tracts of humans. Like other species in the genus Enterococcus, E. faecalis is found in healthy humans and can be used as a probiotic. The probiotic strains such as Symbioflor1 and EF-2001 are characterized by the lack of specific genes related to drug resistance and pathogenesis. As an opportunistic pathogen, E. faecalis can cause life-threatening infections, especially in the nosocomial (hospital) environment, where the naturally high levels of antibiotic resistance found in E. faecalis contribute to its pathogenicity. E. faecalis has been frequently found in reinfected, root canal-treated teeth in prevalence values ranging from 30% to 90% of the cases. Re-infected root canal-treated teeth are about nine times more likely to harbor E. faecalis than cases of primary infections.
Antibiotic sensitivity testing or antibiotic susceptibility testing is the measurement of the susceptibility of bacteria to antibiotics. It is used because bacteria may have resistance to some antibiotics. Sensitivity testing results can allow a clinician to change the choice of antibiotics from empiric therapy, which is when an antibiotic is selected based on clinical suspicion about the site of an infection and common causative bacteria, to directed therapy, in which the choice of antibiotic is based on knowledge of the organism and its sensitivities.
Dalfopristin is a semi-synthetic streptogramin antibiotic analogue of ostreogyrcin A. The combination quinupristin/dalfopristin was brought to the market by Rhone-Poulenc Rorer Pharmaceuticals in 1999. Synercid is used to treat infections by staphylococci and by vancomycin-resistant Enterococcus faecium.
Oritavancin, sold under the brand name Orbactiv among others, is a semisynthetic glycopeptide antibiotic medication for the treatment of serious Gram-positive bacterial infections. Its chemical structure as a lipoglycopeptide is similar to vancomycin.
Enterococcus faecium is a Gram-positive, gamma-hemolytic or non-hemolytic bacterium in the genus Enterococcus. It can be commensal in the gastrointestinal tract of humans and animals, but it may also be pathogenic, causing diseases such as neonatal meningitis or endocarditis.
Ceftobiprole (Zevtera/Mabelio) is a fifth-generation cephalosporin for the treatment of hospital-acquired pneumonia and community-acquired pneumonia. It is marketed by Basilea Pharmaceutica in the United Kingdom, Germany, Switzerland and Austria under the trade name Zevtera, in France and Italy under the trade name Mabelio. Like other cephalosporins, ceftobiprole exerts its antibacterial activity by binding to important penicillin-binding proteins and inhibiting their transpeptidase activity which is essential for the synthesis of bacterial cell walls. Ceftobiprole has high affinity for penicillin-binding protein 2a of methicillin-resistant Staphylococcus aureus strains and retains its activity against strains that express divergent mecA gene homologues. Ceftobiprole also binds to penicillin-binding protein 2b in Streptococcus pneumoniae (penicillin-intermediate), to penicillin-binding protein 2x in Streptococcus pneumoniae (penicillin-resistant), and to penicillin-binding protein 5 in Enterococcus faecalis.
Enterococcus gallinarum is a species of Enterococcus. E. gallinarum demonstrates an inherent, low-level resistance to vancomycin. Resistance is due to a chromosomal gene, vanC, which encodes for a terminal D-alanine-D-serine instead of the usual D-alanine-D-alanine in cell wall peptidoglycan precursor proteins. That is a separate mechanism than the vancomycin resistance seen in VRE isolates of E. faecium and E. faecalis which is mediated by vanA or vanB. This species is known to cause clusters of infection, although it considered very rare. It is the only other known enterococcal species besides E. faecium and E. faecalis known to cause outbreaks and spread in hospitals.
Lancefield grouping is a system of classification that classifies catalase-negative Gram-positive cocci based on the carbohydrate composition of bacterial antigens found on their cell walls. The system, created by Rebecca Lancefield, was historically used to organize the various members of the family Streptococcaceae, which includes the genera Lactococcus and Streptococcus, but now is largely superfluous due to explosive growth in the number of streptococcal species identified since the 1970s. However, it has retained some clinical usefulness even after the taxonomic changes, and as of 2018, Lancefield designations are still often used to communicate medical microbiological test results.
Enterococcus malodoratus is a species of the genus Enterococcus and a gram positive bacteria capable of opportunistic pathogenic response. These microbes have a thick polypeptide layer. Enterococcus can be found in the gastrointestinal tracts of humans and other mammals. In a study on the enterococcal flora of swine, E. malodoratus was found in the intestines and feces. It was not identified within the tonsils of swine, nor within cats, calves, dogs, horse, or poultry. The name "malodoratus" translates to "ill smelling".
ESKAPE is an acronym comprising the scientific names of six highly virulent and antibiotic resistant bacterial pathogens including: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. The acronym is sometimes extended to ESKAPEE to include Escherichia coli. This group of Gram-positive and Gram-negative bacteria can evade or 'escape' commonly used antibiotics due to their increasing multi-drug resistance (MDR). As a result, throughout the world, they are the major cause of life-threatening nosocomial or hospital-acquired infections in immunocompromised and critically ill patients who are most at risk. P. aeruginosa and S. aureus are some of the most ubiquitous pathogens in biofilms found in healthcare. P. aeruginosa is a Gram-negative, rod-shaped bacterium, commonly found in the gut flora, soil, and water that can be spread directly or indirectly to patients in healthcare settings. The pathogen can also be spread in other locations through contamination, including surfaces, equipment, and hands. The opportunistic pathogen can cause hospitalized patients to have infections in the lungs, blood, urinary tract, and in other body regions after surgery. S. aureus is a Gram-positive, cocci-shaped bacterium, residing in the environment and on the skin and nose of many healthy individuals. The bacterium can cause skin and bone infections, pneumonia, and other types of potentially serious infections if it enters the body. S. aureus has also gained resistance to many antibiotic treatments, making healing difficult. Because of natural and unnatural selective pressures and factors, antibiotic resistance in bacteria usually emerges through genetic mutation or acquires antibiotic-resistant genes (ARGs) through horizontal gene transfer - a genetic exchange process by which antibiotic resistance can spread.
Kerry L. LaPlante is an American pharmacist, academic and researcher. She is the Dean at the University of Rhode Island College of Pharmacy. She is a Professor of Pharmacy and former department Chair of the Department of Pharmacy Practice at the University of Rhode Island, an Adjunct Professor of Medicine at Brown University, an Infectious Diseases Pharmacotherapy Specialist, and the Director of the Rhode Island Infectious Diseases Fellowship and Research Programs at the Veterans Affairs Medical Center in Providence, Rhode Island.
