Enterococcus is a type of bacteria commonly found in various environments, including the human body. It is part of the natural flora within the gastrointestinal tract of humans and animals. While often coexisting harmlessly, Enterococcus can cause infections under certain conditions.
Understanding Enterococcus
Enterococcus belongs to a large group of bacteria known as lactic acid bacteria. These are Gram-positive cocci, meaning they appear spherical under a microscope and retain a purple stain in a common laboratory test. They often arrange themselves in pairs or short chains, making them visually similar to some Streptococcus species.
These bacteria are facultative anaerobes, capable of thriving in both oxygen-rich and oxygen-poor environments. This adaptability allows them to survive in diverse settings, including the human gut, soil, water, and even plants. Enterococcus species are also remarkably resilient, tolerating a wide range of conditions such as extreme temperatures and high salt concentrations.
Among the numerous species within the Enterococcus genus, Enterococcus faecalis and Enterococcus faecium are the most frequently encountered in human health. E. faecalis accounts for approximately 90-95% of Enterococcus found in human intestines, while E. faecium makes up about 5-10%. While generally harmless in their natural habitat, these species can become opportunistic pathogens, particularly in individuals with weakened immune systems or those undergoing medical procedures. Their ability to adhere to surfaces and form biofilms, a protective layer of bacteria, contributes to their capacity to cause infections.
Common Infections Caused by Enterococcus
Enterococcus species can cause a variety of infections. These bacteria are a frequent cause of healthcare-associated infections, particularly in healthcare settings, often affecting patients with underlying health conditions or those with indwelling medical devices. Infections typically arise when the bacteria, normally residing in the gut, spread to other parts of the body.
Urinary tract infections (UTIs) are among the most common infections caused by Enterococcus, especially in catheterized patients. Symptoms can include pain or burning during urination, increased urinary frequency, and cloudy or foul-smelling urine. Enterococcus can also lead to bloodstream infections, known as bacteremia. This often occurs secondary to intravenous catheters, UTIs, or abdominal infections, and can manifest with fever, chills, and a rapid pulse.
Infections of the heart valves, called endocarditis, are a serious concern. Enterococcus is a common cause of infective endocarditis, particularly following genitourinary tract infections or procedures. Wound infections, including those in surgical sites, burns, and ulcers, are also commonly attributed to Enterococcus. These can present with redness, swelling, tenderness, and pus leakage at the wound site.
Enterococcus can also cause intra-abdominal and pelvic infections, sometimes leading to abscesses. Though less common, Enterococcus can cause meningitis, an infection of the brain and spinal cord lining, which has been linked to neurosurgery or underlying intestinal issues.
Treating Enterococcus Infections and Antibiotic Resistance
Diagnosis of Enterococcus infections begins with collecting specimens from the suspected site of infection, such as blood, urine, or wound fluid. These samples are then cultured in a laboratory to grow and identify the bacteria. Microscopic examination and further biochemical tests confirm the specific Enterococcus species.
Antibiotic susceptibility testing is performed to determine which antibiotics will be effective against the isolated strain. This testing is important because Enterococcus species are known for their ability to resist many antibiotics. Treatment generally involves antibiotics, but the choice of medication depends on the susceptibility test results. For susceptible strains of E. faecalis, ampicillin or penicillin are often the preferred agents. However, E. faecium is more frequently resistant to commonly used antibiotics like ampicillin.
A challenge in treating Enterococcus infections is the rise of antibiotic resistance, particularly Vancomycin-Resistant Enterococci (VRE). VRE refers to Enterococcus strains that have developed resistance to vancomycin, an antibiotic often used as a last resort for severe infections. This resistance can be intrinsic to the bacteria or acquired through mobile genetic elements.
E. faecium is more resistant to vancomycin, with approximately 80% of E. faecium isolates showing resistance compared to about 10% of E. faecalis isolates. Treating VRE infections can be complex, often requiring alternative antibiotics like linezolid or daptomycin, although treatment options remain limited.
Preventing Enterococcus Infections
Preventing Enterococcus infections, especially resistant strains like VRE, relies on diligent infection control practices. Hand hygiene is a primary defense; healthcare workers should wash hands thoroughly with soap and water or use alcohol-based hand rubs before and after patient contact. This practice reduces the spread of these bacteria.
Proper wound care is also important, as Enterococcus can infect open wounds. Judicious use of antibiotics plays a role in prevention by limiting the development and spread of antibiotic resistance. Healthcare facilities implement infection control measures, including environmental cleaning and disinfection of surfaces and medical equipment, to reduce transmission risk. Isolation precautions, such as placing infected or colonized patients in private rooms, can also help contain the spread of VRE within hospitals.