Enterococcus is a genus of bacteria commonly found in the digestive systems of humans and other animals as a normal part of the gut flora. Structurally, they are Gram-positive cocci, which are spherical bacteria that often appear in pairs or short chains. While a natural inhabitant of the gut, Enterococcus is resilient enough to survive in various environments, including those with high salt concentrations or extreme temperatures.
The Dual Nature of Enterococcus
Enterococcus exemplifies the dual role bacteria can play in the human body. As commensal organisms, they live in the gastrointestinal tract without causing harm. However, the bacteria can become opportunistic pathogens when they move from the gut to other parts of the body. This is particularly true for individuals with compromised immune systems or a weakened state of health.
Two species are most frequently encountered in humans: Enterococcus faecalis and Enterococcus faecium. E. faecalis is the more abundant of the two in the gut, while E. faecium is more often linked to hospital-acquired infections that are challenging to treat.
Common Enterococcal Infections
When Enterococcus spreads outside the gut, it can cause a range of infections frequently seen in hospital environments. Urinary tract infections (UTIs) are a common manifestation, occurring when the bacteria ascend the urinary tract, and patients with urinary catheters are particularly susceptible.
Bloodstream infections, known as bacteremia, can occur when the bacteria enter the blood through a surgical wound or intravenous line. From the bloodstream, the bacteria can infect the heart’s inner lining, a condition called endocarditis. Enterococcus can also contaminate surgical sites and open wounds.
Antibiotic Resistance Challenges
A significant concern with Enterococcus is its resistance to antibiotics. The bacteria possess a high level of natural, or intrinsic, resistance to several classes of antibiotics, including some penicillins and cephalosporins, which complicates treatment. The challenge is magnified by strains that have acquired resistance to more powerful antibiotics.
Vancomycin-Resistant Enterococcus (VRE) is a primary example. Vancomycin is a potent antibiotic used for serious infections, and when enterococci become resistant to it, treatment options become severely limited. This earns them the label of a “superbug,” and the resistance can be transferred to other bacteria through mobile genetic elements.
Diagnosis and Treatment Approaches
Diagnosing an enterococcal infection begins with collecting a sample from the suspected site, such as urine, blood, or wound tissue. The sample is sent to a laboratory to be cultured, which encourages the bacteria to grow so they can be identified. Once identified, the bacteria undergo susceptibility testing to determine which antibiotics will be effective.
For infections caused by strains that are not highly resistant, an antibiotic like ampicillin may be used. For VRE infections, clinicians must turn to other powerful antibiotics, such as linezolid or daptomycin, while severe cases like endocarditis may require a combination of drugs.