What is Enterococcus Infections?
Enterococci are bacteria that don’t require oxygen to survive, and they often appear in short or medium chains. Scientists first identified them in the human gut in 1899. Over time, they were recognized as a unique type of bacteria, separate from streptococci, due to DNA testing and rRNA sequencing studies carried out in 1984.
These bacteria are part of the ESKAPE group, known for being highly resistant to antibiotics. This group includes Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. The World Health Organization highlights them as an increasing cause of hospital and antibiotic-resistant infections in recent decades, posing a serious threat to public health.
There are types of these bacteria that have developed resistance to the antibiotic vancomycin. These are known as Vancomycin-resistant Enterococci (VRE). This resistance was initially detected in animals in 1933, due to the use of a vancomycin-related substance, avoparcin, as an additive in animal feed. The first human cases of VRE were reported in England in 1988.
What Causes Enterococcus Infections?
Enterococci are a type of bacteria that can be found in different environments, such as water, soil, food, sewage, plants, as well as on our skin, in our mouth, and in our large intestine. They make up less than 1% of all the bacteria in our bodies.
There are around 58 known types of enterococci, with the most common ones being E. faecalis and E. faecium. Other types, such as E. avium, E. caccae, E. casseliflavus, E. dispar, E. durans, E. gallinarum, E. hirae, and E. raffinosus have recently been identified as causing bloodstream and endovascular (related to the blood vessels) infections in humans.
Enterococci are very tough bacteria that can survive harsh conditions like common cleaning products. This allows them to live on everyday items found in hospitals. They can also be easily passed around by healthcare workers through their hands.
One of the main ways enterococci can cause severe infections is by colonizing, or setting up camp, in the gastrointestinal tract. This area includes the stomach and intestines. They can be eaten and transported across the intestinal wall where they avoid being destroyed by the body’s protective cells designed to destroy harmful bacteria.
A person’s risk of getting colonized or infected by enterococci, particularly a drug-resistant type known as VRE, increases with previous exposure to antibiotics like vancomycin and cephalosporins, which can disrupt the normal balance of bacteria in the gut. Spending a long time in the hospital, staying in intensive care units, living in long-term care facilities, undergoing hemodialysis for kidney issues, having diabetes or cancer, receiving transplants, suppressing stomach acid, using medical devices like catheters, and exposure to contaminated surfaces or shared medical equipment can also increase the likelihood of getting enterococci/VRE infections.
Risk Factors and Frequency for Enterococcus Infections
Enterococci are a type of bacteria that are the second most common cause of hospital infections in the US, just behind staphylococci. These infections can often resist antibiotics and are commonly associated with certain diseases, blood infections related to medical tubing, and heart infections linked with hospitals. Around 60% of all enterococci infections happen in a healthcare setting, including intensive care units (ICUs).
Enterococci are the third most common cause of heart infections acquired outside of the hospital in North America, following after staphylococcus aureus and streptococcus viridans. This rate is higher than anywhere else in the world. Enterococci also cause 15% to 20% of hospital urinary tract infections. The type of enterococci that is resistant to the antibiotic vancomycin (VRE) is much less common in Europe than in the US where it accounts for around 30% of all enterococci infections.
- There has been a noticeable increase in a subtype of enterococci known as E. faecium. This particular type makes up 35% of enterococci found in hospital infections and 40% of bloodstream infections found in people who have received liver or stem cell transplants.
- The E. faecium type of enterococci is also resistant to more types of antibiotics than other forms of enterococci. It is resistant to vancomycin about 80% of the time and resistant to ampicillin 90% of the time. This contrasts with E. faecalis enterococci which are only resistant to vancomycin 10% of the time and are usually not resistant to ampicillin.
Signs and Symptoms of Enterococcus Infections
When diagnosing a patient, it’s crucial to gather a detailed medical history. This should include information about any fevers, antibiotics used and for how long, instances of infection by drug-resistant organisms, and stays in a hospital or care home. In addition, doctors need to know about the patient’s history of cancer screening, HIV screening, past surgeries, and any existing medical conditions like uncontrolled diabetes or recent heart surgeries. They should also ask about nonhealing wounds and any external devices like catheters. A full physical examination is also necessary, especially when the cause of a blood infection is unknown.
Enterococci often cause urinary tract infections (UTIs), particularly in patients already ill. These infections are common in a hospital environment, and may be associated with issues such as urinary obstruction or catheter use. UTIs can be complicated, and could lead to kidney infection, abscesses around the kidney, or chronic prostate infection, all of which can cause a bacterial infection in the blood. UTIs are more likely to be complicated in cases of diabetes, pregnancy, the use of urinary catheters, a weakened immune system, bladder issues, obstructions, or kidney stones. Blood infections can also arise from other sources, such as IV lines, intra-abdominal infections, wound infections, and bone infections.
Infection of the heart’s inner lining (endocarditis) by enterococci is becoming more common, and accounts for 8 to 32% of blood infections caused by enterococci. This is particularly witnessed in older patients who have had heart valve implants. Symptoms of heart infection may include a fever above 100.4 degrees Fahrenheit, skin nodules (Osler nodes), red skin spots (Janeway lesions, Roth spots), a new heart murmur, blood in urine or under the nails (splinter hemorrhages). Enterococci can also be associated with abdominal infections.
Meningitis, or inflammation of the brain and spinal cord membranes, is not common with enterococci but can occur, especially in relation to procedures or devices in the brain, leaks of brain fluid, trauma, defects in the central nervous system (CNS), or intense blood infections in patients with a weakened immune system. Symptoms can include changes in mental status, headache, neck stiffness, fever, lethargy, nausea, and vomiting. Enterococci can also cause surgical-site infections, ulcers in people with diabetes, infections in artificial joints, eye infections, and failure of root canals in the teeth. Cases of severe enterococcal infections in newborns have been reported in the United States.
Testing for Enterococcus Infections
Before starting antibiotic treatment, your doctor might need to take a sample of your body fluids or blood to carry out a culture test. Additionally, you might have to undergo a chest X-ray, an echocardiogram (a heart scan), a CT scan of your abdomen, or a colonoscopy (an examination of the colon) depending on the specific characteristics of the infection.
Enterococci, the bacteria that we are discussing, are usually seen as short chains, pairs, or single oval-shaped cells under the microscope. They can grow under various conditions, including environments with high salt concentration and a wide range of temperatures. Although they mostly do not cause the breakdown of red blood cells (hemolysis), some can.
These bacteria are identified in the lab by multiple properties, including being negative for catalase and urease, being positive for Lancefield group D antigen, being able to break down chemicals called esculin and PYR in the presence of bile salts, and more. The identification of the specific type of Enterococcus is based on how they break down carbohydrates and other substances, their ability to move, and their color.
More recently, genetic testing methods, have taken over traditional chemical tests. These include a range of technologies that can identify Enterococcus through specific genes and proteins, and even determine which antibiotics they are resistant to.
The sensitivity of Enterococcus to antibiotics like penicillin, vancomycin, and aminoglycoside should be regularly tested. If the bacteria are found to resist these antibiotics, more tests will be done to check whether they are sensitive to other antibiotics like daptomycin and linezolid. The DENOVA tool is used to predict if patients with Enterococcus in their blood have endocarditis, an infection of the heart’s inner lining. In some cases, doctors suggest undergoing an echocardiogram to detect conditions like this.
Also, doctors recommend colonoscopies for patients with Enterococcus in their blood or endocarditis from an unknown source. This is because there is a high occurrence of new cancerous cells in the colon in such patients, similar to conditions caused by other bacteria such as Streptococcus bovis and Clostridium septicum.
Treatment Options for Enterococcus Infections
When it comes to treating an infection caused by enterococci, the type of infection and how responsive the bacteria are to antibiotics play key roles. Enterococci are a type of bacteria that live in your intestines and urinary tract. Normally, they don’t cause problems, but they can cause infections in certain cases.
There are different types of enterococci, and some are more harmful than others. For instance, Enterococcus faecalis infections are usually more severe than Enterococcus faecium infections. Also, if you have a bloodstream infection caused by Enterococcus faecalis, there’s a higher chance you could also develop endocarditis, which is an infection of the heart valve.
Common antibiotics like penicillin and ampicillin can slow the growth of enterococci, but they usually can’t kill the bacteria entirely. The same goes for two other types of antibiotics, vancomycin and aminoglycosides. And because aminoglycosides don’t easily penetrate bacteria cells, they are often used together with another antibiotic that can.
Penicillin or ampicillin is often paired with an antibiotic from the aminoglycoside group. Using vancomycin with an aminoglycoside can potentially harm the kidneys, so this combination is generally reserved for instances when hypersensitivity (allergy) is a concern or there’s a high resistance to other antibiotics.
The best approach to treat an infection depends on the specific condition. For instance, a urinary tract infection (or UTI) might initially be treated with antibiotics such as Nitrofurantoin, Amoxicillin or Fosfomycin. If the UTI is complicated, doctors might use the antibiotics Ampicillin or Levofloxacin.
If you were to have an infection in your bloodstream or endocarditis, an infection of the heart valve, doctors would typically use the antibiotics Ampicillin, Penicillin or Ceftriaxone, and might add another drug like Gentamicin, Streptomycin or Vancomycin as well.
Your treatment may change if certain medications aren’t effective. It’s also worth noting that there it’s still uncertain what the best treatment is for infections caused by a particularly resistant type of Enterococcus, Enterococcus faecium.
There are also some promising new therapies in development. Researchers are looking into the potential of probiotics, compounds that can prevent or reverse gut colonization by certain bacteria, as well as methods to limit bacterial adherence and biofilm formation on medical devices.
Scientists are also studying other innovative approaches, such as using short-chain fatty acids (SCFA) and bacteriophages, viruses that specifically infect bacteria, in treating enterococcal infections. Gene editing techniques, like CRISPR, are also being proposed to limit the ability of bacteria to share resistance genes.
In summary, various treatments are available for enterococcal infections, and the best approach depends on the specifics of the infection and the patient’s overall health condition.
What else can Enterococcus Infections be?
When doctors initially examine bacteria cultures from urine, blood, spinal fluid, tissue, other body fluids or wounds, they often find a type of bacteria called “Gram-positive cocci in chains.” At this early stage, the exact type of bacteria causing the infection could be from a wide range, such as Group A, B, or C Streptococci, Streptococcus bovis, various types of enterococci, and others.
However, if the patient got sick while in a hospital, which is known as a nosocomial infection, and is very ill, doctors will typically start treating the patient for an Enterococcus infection even before the final, specific diagnosis is confirmed by the culture results.
Infections of the urinary tract, blood, heart, brain, abdomen, and wounds could be caused by a huge array of different bacteria that can all look like an Enterococcus infection. If the doctor has a reason to believe that the bacteria causing the infection may be resistant to regular antibiotics, they’ll start treating the patient with broad-spectrum antibiotics, which can kill a wide range of bacteria, while waiting for lab results to confirm the exact type of bacteria causing the infection and its resistance profile.
What to expect with Enterococcus Infections
Infections from VRE (Vancomycin-Resistant Enterococci, a type of bacteria resistant to many antibiotics) have been found to double health risks and increase costs when compared to infections from bacteria that are still responsive to the drug vancomycin. This remains the case even after treatments specific to VRE have been made available.
VRE infections also tend to extend the duration of hospital stays and increase the likelihood of discharges to long-term care facilities and re-admissions to the hospital. Enterococcal endocarditis (an infection of the heart’s inner lining), enterococcal bacteremia (a bloodstream infection), and enterococcal meningitis (an infection of the membranes surrounding the brain and spinal cord) have mortality rates of 11-35%, 25%, and 20% respectively.
Possible Complications When Diagnosed with Enterococcus Infections
Research hints at a link between gut bacteria called E. gallinarum making their way into other areas of the body and the production of autoantibodies, as found in conditions like inflammatory bowel disease.
Another type of bacteria, E. faecalis, can lead to genetic instability and inflammation in the lining of the colon, and can potentially cause colorectal cancer. This was backed up by the higher amount of E. faecalis found in the feces of colon cancer patients when compared to healthy individuals.
A compound released by Enterococcal bacteria called cytolysin can damage liver cells. This is common among patients with alcoholic hepatitis and is directly related to the severity of the disease and the death rate. As a result, specific treatments targeting cytolytic enterococci bacteria are suggested for these patients.
A high count of fecal enterococci bacteria is linked with a severe condition called graft versus host disease (GVHD), often noticed in patients who have undergone a bone marrow transplant. Interestingly, a higher amount of enterococcal bacteria compared to other normal gut bacteria was found in patients with GVHD who consumed a diet high in lactose. This suggests that a lactose-free diet or lactase-based treatment may benefit these patients to control the growth of enterococci bacteria.
Interestingly, strains of E. faecalis and E. faecium are used as probiotics in common treatments for diarrhea, irritable bowel syndrome, high blood cholesterol, and to enhance immunity. They’re also used in animals to promote growth and in food fermentation. While no safety issues or infections from these probiotics have been reported as of now, it’s important to monitor them closely to prevent any problematic strains from developing.
Preventing Enterococcus Infections
It’s crucial for patients to keep their hands clean and take good care of areas where catheters are inserted to prevent infections. Watching out for redness around these areas is also important, as it could indicate a problem. If patients start feeling unwell or experience a sudden spike in temperature, they should reach out to their doctors immediately. Additionally, patients should keep track of how long their catheters and artificial implants have been in place, and make sure their healthcare providers are also aware of this information.
