Enterococcus faecalis is a widespread bacterium commonly found within the human gastrointestinal tract. This microorganism has a complex standing in the medical community, recognized both as a normal inhabitant of the body and as a potential cause of serious infections. Understanding its characteristics is important due to its frequent presence and increasing relevance in healthcare settings.
Microbiological Profile
Enterococcus faecalis is classified as a Gram-positive bacterium, meaning its cell wall retains a violet stain during a specific laboratory test, appearing blue or purple under a microscope. These bacteria are spherical or ovoid, typically measuring between 0.5 to 2 micrometers in diameter. They often arrange themselves in pairs or short chains.
The bacterium belongs to the Enterococcus genus, established in 1984 to reclassify certain species previously grouped with Streptococcus. Genetic differences, particularly in their ribosomal RNA, distinguish them as a separate genus. E. faecalis is also non-motile and does not form spores.
Natural Habitat and Survival Traits
The primary dwelling of Enterococcus faecalis is the intestinal tract of humans and other warm-blooded animals, where it normally resides without causing harm. It can also be found in other areas like the mouth and vagina. Beyond the body, E. faecalis is present in diverse natural environments, including soil, water, and food, often in areas contaminated by feces.
This bacterium is resilient, surviving in conditions challenging for many other microorganisms. It tolerates a wide range of temperatures, from approximately 10°C to 45°C, and can even survive at 60°C for about 30 minutes. E. faecalis also withstands high salt concentrations, up to 6.5% sodium chloride, and can grow in environments with a wide pH range, from 4.5 to 10. This hardiness allows it to persist on dry surfaces for extended periods, ranging from 5 days to 4 months.
The Dual Role in Human Health
Enterococcus faecalis exhibits a dual nature in human health, functioning both as a harmless commensal and as an opportunistic pathogen. As a commensal, it is a regular component of the gut microbiota, contributing to bodily functions such as food digestion. In healthy individuals, E. faecalis remains confined to its normal habitats and does not cause illness.
However, E. faecalis can become an opportunistic pathogen, particularly in individuals with compromised immune systems or those who are already ill. Infections frequently occur in hospital settings, often called nosocomial infections. Common infections include urinary tract infections (UTIs), especially those associated with catheterization. It can also lead to more severe conditions such as endocarditis, an infection of the heart lining, and bacteremia, a bloodstream infection.
Antibiotic Resistance and Treatment Challenges
A concern with Enterococcus faecalis is its ability to resist many antibiotics, making infections difficult to treat. The bacterium possesses intrinsic, or natural, resistance to certain classes of antibiotics, including most beta-lactams like cephalosporins. It also exhibits natural resistance to aminoglycosides, such as gentamicin, due to the drug’s inability to enter the bacterial cell.
Beyond its inherent resistance, E. faecalis can acquire additional resistance to other powerful drugs through genetic mutations or by exchanging genetic material with other bacteria. A notable example is Vancomycin-resistant Enterococcus (VRE), which refers to E. faecalis strains that have developed resistance to vancomycin, a last-resort antibiotic. VRE is a public health concern, leading to prolonged hospital stays and increased mortality rates in hospitalized patients. The bacterium’s capacity to form biofilms, protective layers of bacteria on surfaces like medical devices, further complicates treatment by shielding the bacteria from antibiotics and the body’s immune response.