Enterococcus faecalis is a common bacterium found in various environments, including the human body. This microorganism belongs to a larger group known as Enterococci, which encompasses at least 18 different species. While generally harmless in its usual habitats, E. faecalis can become a concern if it spreads to other areas or infects individuals with compromised immune systems. Understanding this bacterium often begins with examining its appearance under a microscope.
Visualizing Enterococcus faecalis Under the Microscope
When observed through a light microscope, Enterococcus faecalis displays visual characteristics for initial identification. These bacteria are spherical or ovoid-shaped cells, measuring between 0.6 and 1.0 micrometers in diameter. They are arranged in pairs, known as diplococci, or in short chains, resembling streptococci.
A Gram stain procedure further distinguishes E. faecalis. This bacterium is classified as Gram-positive, meaning its thick peptidoglycan cell wall retains the crystal violet stain, appearing purple or blue. This staining reaction, along with its characteristic shape and arrangement, provides preliminary information in a laboratory setting.
Where Enterococcus faecalis Resides
Enterococcus faecalis inhabits various environments. Its primary habitat is the gastrointestinal tract of humans and warm-blooded animals. Within the human body, it can also be found in the mouth and vaginal tract.
Beyond living hosts, E. faecalis is widespread in nature. It resides in soil and water, particularly in areas contaminated by fecal matter. The bacterium’s ability to tolerate harsh conditions, such as varying temperatures (10°C to 45°C), high salt concentrations (6.5% NaCl), and a wide pH range (up to 9.6), contributes to its prevalence in these diverse settings. In these environments, it often plays a neutral or even beneficial role as a commensal organism.
Clinical Significance of Enterococcus faecalis
Despite its common presence, Enterococcus faecalis is recognized as an opportunistic pathogen, meaning it can cause infections under certain circumstances. This occurs when the bacterium leaves its usual habitat or infects individuals with weakened immune systems. E. faecalis is a leading cause of healthcare-associated infections.
Common infections caused by E. faecalis include urinary tract infections (UTIs), wound infections, and bloodstream infections (bacteremia). It can also lead to more severe conditions like endocarditis, an inflammation of the heart’s inner lining, and in rare cases, meningitis. A challenge in treating E. faecalis infections is its increasing resistance to various antibiotics. Strains resistant to vancomycin, known as vancomycin-resistant Enterococcus (VRE), are problematic and require specific treatment approaches.
Identification Methods Beyond Microscopy
While microscopic examination offers initial insights into Enterococcus faecalis, definitive identification requires further laboratory tests. Biochemical tests are employed to differentiate E. faecalis from other bacterial species. These tests assess specific metabolic activities, such as its ability to ferment certain sugars or produce particular enzymes, like being catalase-negative and PYR-positive.
Another method involves observing its growth on selective media like bile esculin agar, where E. faecalis produces a characteristic black precipitate. For accurate identification and to detect antibiotic resistance genes, molecular methods like Polymerase Chain Reaction (PCR) are increasingly used. These advanced techniques confirm initial microscopic findings, aiding clinical diagnosis and treatment.