Enterococcus faecalis and Enterococcus faecium are close cousins that live harmlessly in almost everyone’s gut. They cause trouble mostly in people who are already sick or in hospital. On a lab report the two names matter, because they tend to cause different problems and respond differently to drugs. Faecalis is the better stick-er and the one more linked to heart-valve infections, while faecium is the harder one to kill with antibiotics.
Which One Is More Dangerous
A bloodstream infection, which your report may call bacteremia, is the most serious way either bacterium shows up. Within 90 days of one, about 45% of faecium patients had died versus 29% of faecalis patients.1Open Forum Infectious Diseases. Comparing Enterococcus faecalis and Enterococcus faecium Bloodstream Infections’ Severity and Mortality Survival was worse for faecium within the first 100 days after the infection.2Open Forum Infectious Diseases. Comparing Enterococcus faecalis and Enterococcus faecium Bloodstream Infections’ Severity and Mortality Even when both are vancomycin-resistant, faecium carries more than double the in-hospital death risk of faecalis.3PubMed Central. Comparison of the clinical characteristics and outcomes associated with vancomycin-resistant Enterococcus faecalis and vancomycin-resistant E. faecium bacteremia Much of that extra danger comes from having fewer drugs that still work, since faecalis usually still responds to penicillin-type drugs.4PubMed Central. Comparison of the clinical characteristics and outcomes associated with vancomycin-resistant Enterococcus faecalis and vancomycin-resistant E. faecium bacteremia
These figures describe groups of hospital patients, many already critically ill, and they cannot predict what will happen to one person. Age, kidney or liver disease, cancer, and a weakened immune system push the outlook in either direction regardless of species. Starting an antibiotic the bacteria are sensitive to early in the illness is one of the things that most improves the odds, and the care team can act on that.
Where the bacteria were found matters a great deal. Enterococci are common in urine samples, and a positive urine culture in someone with no fever, burning or pain may just reflect colonization or contamination, which often needs no antibiotics. A positive blood culture is treated as serious because blood is normally sterile, so any growth there generally means bacteria have entered the bloodstream and need prompt treatment. Occasionally a blood sample picks up skin bacteria during collection, which is one reason doctors repeat cultures before deciding. It is fair to ask the care team which body site the bacteria came from. When the lab names the species, useful questions include whether the strain is resistant to ampicillin or vancomycin, whether blood cultures were taken and repeated, and, if it was faecalis in the blood, whether a heart scan is planned.
Where They Live and Why They Infect
E. faecalis and E. faecium are the two most abundant enterococci in human stool.5PubMed Central. Enterococci and Their Interactions with the Intestinal Microbiome Finding them in a gut-related sample is therefore normal and not proof of infection.
To cause infection, a gut bacterium has to end up somewhere it shouldn’t be. Urinary catheters, IV lines and surgical wounds, especially after abdominal surgery, give gut bacteria a physical path into the bladder or bloodstream. Broad-spectrum antibiotics wipe out many other gut bacteria, and enterococci, which many of these drugs do not kill, can multiply to take their place. Older age, kidney disease, diabetes and weakened immunity make it easier for bacteria to take hold once they get in. Healthy people with no lines, surgery or hospital stay very rarely develop serious enterococcal infections.
Hospitals have shifted the balance toward faecium. In UK bloodstream infections, faecium rose from 31% of enterococcal cases in 2001–3 to 51% in 2017–19.6PubMed Central. Replacement of Enterococcus faecalis by Enterococcus faecium as the predominant enterococcus in UK bacteraemias In one European hospital, ampicillin-resistant faecium went from 2% of enterococcal infections in 1994 to 32% in 2005.7PubMed. Ecological replacement of Enterococcus faecalis by multiresistant clonal complex 17 Enterococcus faecium Hospital faecium strains since 2010 survive alcohol hand-rub chemicals about 10 times better than older strains.8PubMed Central / Science Translational Medicine. Increasing tolerance of hospital Enterococcus faecium to handwash alcohols Around a patient carrying faecium, soap-and-water washing and thorough cleaning matter.
Why Faecium Is Harder to Treat
Ampicillin, a penicillin-type antibiotic, is the standard first choice for enterococcal infections. Faecium carries several ampicillin-resistance genes that faecalis lacks,9PubMed Central. Genome-Wide Identification of Ampicillin Resistance Determinants in Enterococcus faecium so it is far more often strongly resistant. Changes in the drug’s target that cause resistance have been found in faecium but not reported in faecalis.10PubMed Central. Mechanisms of resistance to imipenem and ampicillin in Enterococcus faecalis
VRE means vancomycin-resistant enterococcus, a label you may see on a report or an isolation sign. In European bloodstream infections, vancomycin resistance is found mainly in faecium.11PubMed Central. The ongoing challenge of vancomycin-resistant Enterococcus faecium and Enterococcus faecalis in Europe: an epidemiological analysis of bloodstream infections The two species also tend to carry different vancomycin-resistance genes.12PubMed Central. Vancomycin-Resistant Enteroccus Faecium and Enterococcus Faecalis Isolated from Education Hospital of Iran
Resistance can spread. Both species pick up resistance genes from other bacteria through shared packages of DNA,13PubMed Central. Horizontal Gene Transfer and the Genomics of Enterococcal Antibiotic Resistance so resistance can pass between strains and even to other kinds of bacteria.14PubMed Central. Let Me Upgrade You: Impact of Mobile Genetic Elements on Enterococcal Adaptation and Evolution
On your report, the lab grows the bacteria with different antibiotics and lists which ones stop it, usually as sensitive or resistant. It is a guide to which drug to choose. Resistance to ampicillin usually means doctors move to a different intravenous drug, often one reserved for harder cases. If VRE appears, a hospital may place you in a single room or ask staff and visitors to wear gowns and gloves to limit spread. Resistance describes how many drugs work, not how aggressive the bacteria are.
It is a mistake to assume faecalis is always the easy one. Faecalis can also be vancomycin-resistant, so a VRE label alone does not tell you which species it is. Even then it often still responds to ampicillin, which keeps a good treatment option open.
Faecalis and Heart Valve Infections
Endocarditis is an infection of the heart’s valves or lining. About 1 in 5 people with faecalis in the blood developed it, versus about 1 in 40 with faecium.15European Heart Journal. Characteristics and outcomes in patients with infective endocarditis caused by Enterococcus faecium and Enterococcus faecalis About 4 in 10 faecalis endocarditis patients had had a faecalis bloodstream infection in the previous year,16European Heart Journal. Characteristics and outcomes in patients with infective endocarditis caused by Enterococcus faecium and Enterococcus faecalis so a repeat faecalis bloodstream infection is a warning sign worth raising with doctors.
Faecium heart-valve infection is rarer, but when it happens it led to clots or debris travelling to other organs in about 6 in 10 cases, versus 1 in 10 with faecalis.17European Heart Journal. Characteristics and outcomes in patients with infective endocarditis caused by Enterococcus faecium and Enterococcus faecalis Over about three years, more than half of people with either type had died.18European Heart Journal. Characteristics and outcomes in patients with infective endocarditis caused by Enterococcus faecium and Enterococcus faecalis
After faecalis in the blood, some symptoms are worth reporting. A fever that keeps returning or does not settle despite antibiotics should be mentioned, as should night sweats. A new heart murmur, which a doctor may hear with a stethoscope, can be an early sign that a valve is damaged. Unusual tiredness, breathlessness or unexplained weight loss can build slowly and are easy to dismiss. Small painful spots on the fingers or toes, or sudden weakness or speech trouble resembling a stroke, are urgent signs because infected material may have travelled.
Testing usually means repeated blood cultures to see whether the bacteria clear, plus an ultrasound of the heart, sometimes done through the throat for a closer view. Treatment of a heart infection typically lasts several weeks of IV antibiotics.
Catheters and Urinary Infections
Enterococci are a frequent cause of urinary infections linked to catheters.19mBio. Antibody-Based Therapy for Enterococcal Catheter-Associated Urinary Tract Infections Faecalis sticks to catheter materials in much higher numbers than faecium.20PubMed. In vitro adherence of Enterococcus faecalis and Enterococcus faecium to urinary catheters It uses hair-like surface fibres to grab a body protein that coats catheters.21mBio. Antibody-Based Therapy for Enterococcal Catheter-Associated Urinary Tract Infections A catheter also gives bacteria a continuous path from the skin and surroundings into the bladder, and the longer it stays in, the greater the chance they take hold.
A biofilm is a slimy protective film bacteria build on surfaces, shielding them from drugs. In one hospital, over 9 in 10 faecalis blood strains made biofilm versus 2 in 10 faecium strains.22PubMed Central. Molecular characterization and biofilm formation ability of Enterococcus faecium and Enterococcus faecalis bloodstream isolates from a Chinese tertiary hospital in Beijing Antibiotics reach the free-floating bacteria in urine but struggle against the film on the tube, so the infection can return after treatment. That is why infected catheters often need replacing, not just antibiotics. Doctors often change the catheter before or early in the antibiotic course so the new tube starts without the old film, and if the catheter is no longer needed, removing it is often the most effective step.
If you live with a catheter, bacteria in the urine are very common, and without symptoms they often do not need treatment. Antibiotics given needlessly can encourage resistance. Fever, new pain in the lower belly or back, chills, or sudden confusion, especially in older people, are reasons to call promptly. Ask the care team how often the catheter should be changed, since the schedule depends on the type. Washing hands before and after handling the bag or tube, and keeping the bag below bladder level, reduces the spread of bacteria.
How Each Is Treated
Most faecalis infections are treated with ampicillin or amoxicillin.23PubMed Central. Comparison of the clinical characteristics and outcomes associated with vancomycin-resistant Enterococcus faecalis and vancomycin-resistant E. faecium bacteremia For heart infections, a second drug is often added so the pair kills the bacteria better than either alone; gentamicin has been the traditional partner, and ceftriaxone is now often used instead. Gentamicin can harm the kidneys and hearing, so doctors weigh that against the benefit and check the strain’s sensitivity first. Strains with high-level gentamicin resistance cancel that boost,24PubMed Central. Relationship between the level of acquired resistance to gentamicin and synergism with amoxicillin in Enterococcus faecalis so the pairing is useless against them,25PubMed Central. High Level Resistance to Aminoglycosides in Enterococci from Riyadh and doctors need a different partner drug or approach.
Linezolid and daptomycin are the main drugs for VRE. In reported cases of brain or spinal-fluid VRE faecium infection, linezolid cured 15 of 19.26PubMed. Treatment Considerations for CNS Infections Caused by Vancomycin-Resistant Enterococcus faecium: A Focused Review of Linezolid and Daptomycin Lab tests show daptomycin plus fosfomycin or linezolid can work together against resistant strains, though this is not yet proven in patients.27PubMed. Assessment of the in vitro synergy of daptomycin plus linezolid against multidrug-resistant enterococci28PubMed Central. Fosfomycin synergy in vitro with amoxicillin, daptomycin, and linezolid against vancomycin-resistant Enterococcus faecium from renal transplant patients with infected urinary stents
Day to day, identifying the species and its drug sensitivities takes two to three days after the sample is taken. Early treatment is often chosen based on likely bacteria rather than confirmed results, and some seriously ill people get a broader combination first and narrow it later. Once the report arrives, doctors often switch to a better-matched drug, which is normal and not a sign the first choice was wrong.
Linezolid comes as tablets as well as by IV, so some people can finish treatment at home once stable. Longer courses involve blood tests to watch for effects such as a drop in blood cell counts. Daptomycin is given by IV, and doctors may check muscle enzymes in the blood during longer courses. Treatment length depends on the site: a bladder infection takes far less time than a heart-valve infection.
Are Enterococcus Probiotics Safe
Enterococci are sold in some probiotics and used in food production.29PubMed. Risks associated with enterococci as probiotics No enterococcal probiotic is approved by the US FDA to treat any disease,30PubMed. Risks associated with enterococci as probiotics which means there is no official confirmation that these products work. Europe’s food safety authority concluded enterococci don’t meet its standard for presumed safety.31PubMed. Risks associated with enterococci as probiotics The reason is their ability to swap resistance and virulence genes, which raises concern even for harmless strains.32PubMed Central. Evaluation of Enterococcal Probiotic Usage and Review of Potential Health Benefits, Safety, and Risk of Antibiotic-Resistant Strain Emergence Close cousins of the same species cause hospital infections, so a harmless label on one strain does not guarantee another is harmless.
Still, specific strains, such as two from kimchi, have been tested and found to carry no resistance or harmful genes.33PubMed Central. Evaluation of Safety and Probiotic Potential of Enterococcus faecalis MG5206 and Enterococcus faecium MG5232 Isolated from Kimchi, a Korean Fermented Cabbage Safety testing applies to a particular strain, so check whether the label names the exact strain, not just the species.
Avoid enterococcal probiotics if you are in hospital, have a weakened immune system, or have a heart valve problem or artificial valve. If you are having cancer treatment or similar therapy that lowers immunity, ask your doctor before taking any probiotic. If you have a catheter or lines and are taking an enterococcal probiotic, mention it to your care team so they can advise. Probiotics built on other species, such as certain lactobacilli, have longer safety records for most healthy people.