Enterococci were historically classified under Streptococcal Lancefield Group D but are now recognized as a distinct genus due to unique biochemical and genetic traits.
They are opportunistic pathogens, normally harmless in the gut but capable of causing serious healthcare-associated infections.

🔬 Characteristics

Gram-positive cocci 🦠, oval-shaped, typically arranged in pairs (diplococci) or short chains.
Facultative anaerobes, resilient and able to survive in harsh conditions (high salt, bile salts, and variable pH).
Capable of growing in bile salt-containing media, helping to distinguish them from other Gram-positive cocci.
Show variable haemolysis: alpha, beta, or gamma (none).

🧫 Main Species

Enterococcus faecalis – more common in human infections, often sensitive to ampicillin.
Enterococcus faecium – less common but highly resistant; associated with Vancomycin-Resistant Enterococci (VRE).

🌍 Source

Normal commensals of the gastrointestinal tract and female genital tract.
Cause disease when translocated to normally sterile sites (urinary tract, bloodstream, heart valves).
Healthcare-associated: frequently implicated in nosocomial infections.

🦠 Pathogenicity

Urinary Tract Infections (UTIs): Especially in catheterised or elderly inpatients.
Biliary sepsis: Often post-surgical or in obstructive jaundice.
Abdominal wound infections: Common after laparotomy or intra-abdominal sepsis.
Endocarditis: Subacute course, particularly in patients with prosthetic or damaged valves.
Can cause bacteraemia and line-associated sepsis in immunocompromised patients.

🧪 Investigations

Culture on bile salt-containing media (e.g. bile esculin agar). They hydrolyse esculin in the presence of bile.
Biochemical tests: PYR-positive, growth in 6.5% NaCl distinguishes them from other streptococci.
Blood culture is essential in suspected endocarditis or systemic infection.

⚠️ Resistance

E. faecium – commonly resistant to penicillin and aminoglycosides.
Both E. faecalis and E. faecium are intrinsically resistant to cephalosporins.
Vancomycin-Resistant Enterococci (VRE): Emerging nosocomial problem, especially in ICU/oncology units.

💊 Sensitivities

Ampicillin: Effective for many E. faecalis strains, less so for E. faecium.
Vancomycin: Historically first-line, but resistance is now common in E. faecium.
Other options (depending on sensitivities): Linezolid, Daptomycin, Tigecycline.

🛠️ Management

UTIs: Oral amoxicillin (if sensitive); nitrofurantoin sometimes used.
Endocarditis: Often requires prolonged IV therapy with a cell wall-active agent (ampicillin or vancomycin) plus an aminoglycoside (gentamicin) for synergy.
VRE infections: Require specialist input – agents include linezolid or daptomycin.
Strict infection control measures (isolation, hand hygiene) to prevent VRE spread.

📌 Key Exam Pearls

Enterococci are the second most common cause of nosocomial infections after staphylococci.
Intrinsically resistant to cephalosporins – classic exam trick.
VRE is a red-flag in UK hospital microbiology reports and requires specialist consultation.
Endocarditis due to enterococci often requires combination therapy and has a high relapse rate.

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Enterococci

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