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Gram-positiveCocciCatalase-negative

Enterococcus faecium

Gram-positive, catalase-negative coccus found in chains, notable for intrinsic vancomycin resistance (VRE) and as a leading cause of nosocomial urinary tract infections, bacteremia, and endocarditis.

Organism Card

DomainMust know
Identity
  • G+ve cocci in chains/pairs; facultative anaerobe
  • Formerly classified as Group D streptococci (Lancefield D) [1][2]
  • Now genus Enterococcus; E. faecium is the more resistant species vs E. faecalis
  • Commensal of GI and GU tract
Lab discriminator
  • Catalase −ve (vs staphylococci catalase +ve)
  • PYR +ve (shared with GAS; but enterococci are bile-esculin +ve, GAS is not)
  • Bile-esculin +ve + growth in 6.5% NaCl → distinguishes enterococci from other streptococci
  • E. faecium vs E. faecalis: faecium is ampicillin-resistant (MIC usually high); faecium more likely VRE
Reservoir / transmission
  • Normal flora of human GI tract and female genital tract [1][2]
  • Source: GI/GU tract; enters by pathologies/manipulations [2]
  • Nosocomial spread via contaminated hands, devices (Foley catheters, IV lines) [3]
  • Survives on environmental surfaces; resistant to drying and disinfectants
Key virulence
  • Intrinsic low-level resistance to multiple antibiotics → survival advantage in hospital
  • Biofilm formation on indwelling devices (catheters, prosthetic valves) [3]
  • Intrinsically resistant to cephalosporins and aminoglycosides (as monotherapy) [4][5]
  • Acquired vancomycin resistance (VanA, VanB operons) → defines VRE, major nosocomial threat
Clinical syndromes
  • UTI: 2nd most common cause in complicated/nosocomial UTI (Enterococcus spp 11%) [6][7]
  • Infective endocarditis: subacute; source GI/GU manipulation; native or prosthetic valve [1][2]
  • Nosocomial bacteraemia (esp catheter-related, post-abdominal surgery) [3]
  • Intra-abdominal/pelvic infections (often polymicrobial)
  • PD-related peritonitis (G+ve organism in CAPD patients) [8]
  • Neonatal sepsis (less common than GBS; E. faecalis more common than faecium in neonates)
Diagnosis
  • Blood culture (≥2 sets), urine C/ST, PD fluid culture as appropriate
  • Gram stain: G+ve cocci in chains (may mimic streptococci)
  • Species ID + susceptibility testing essential (ampicillin, vancomycin, high-level gentamicin)
  • High-level aminoglycoside resistance (HLAR) screen: if HLAR +ve → synergy with ampicillin lost
Treatment
  • Ampicillin (IV) or amoxicillin-clavulanate (PO, Augmentin) for susceptible Enterococcus [4][5]
  • E. faecium is usually ampicillin-resistant → use vancomycin [4][5]
  • 3rd-gen cephalosporins are NOT effective (intrinsic resistance) [4][5]
  • Aminoglycosides NOT effective as monotherapy (intrinsic low-level resistance); used for synergy with ampicillin/vancomycin in IE [1][2]
  • For VRE E. faecium: linezolid or daptomycin (last resort agents)
  • IE regimen: IV ampicillin + gentamicin for 4–6 wks (if susceptible); vancomycin if ampicillin-R [2]
Prevention
  • Contact precautions for VRE in hospital; hand hygiene paramount [3]
  • Antibiotic stewardship to limit selection pressure (restrict broad-spectrum cephalosporins/carbapenems)
  • No vaccine available
  • IE prophylaxis: amoxicillin before high-risk dental procedures in high-risk cardiac patients
Classic traps
  • Do NOT use cephalosporins for Enterococcus — a classic exam trap [4][5]
  • E. faecium ≠ E. faecalis: faecium is more drug-resistant (ampicillin-R, more VRE)
  • Neonatal meningitis G+ve cocci in chains → think GBS first, not E. faecalis [9][10]
  • S. bovis IE → think colonic neoplasm; Enterococcal IE → think GU/GI manipulation [2]
  • Nitrofurantoin can treat enterococcal lower UTI (but not upper tract — poor tissue levels) [4]

Exam Intelligence

  1. GC 102 [3]: Enterococcus listed as a key pathogen in Foley catheter–related UTI in immunocompromised hosts; device-related infections are difficult to eradicate without catheter removal due to biofilm.

  2. Multiple senior notes [4][5] emphasize the critical teaching point: "Enterococcus is intrinsically resistant to cephalosporins and aminoglycosides — therefore should use Augmentin or nitrofurantoin." This is the single most testable pharmacology fact for Enterococcus on HKUMed papers.

  3. IE lectures [1][2]: Enterococcus is classified under "Group D streptococci" for IE teaching; source is GI/GU tract; empirical subacute IE regimen = IV ampicillin + IV gentamicin. The aminoglycoside here is used for synergistic bactericidal activity, not as monotherapy.

  4. UTI teaching [6][7]: Enterococcus spp accounts for ~5% of uncomplicated UTI but ~11% of complicated UTI — frequency rises with catheterisation and hospitalisation.

  5. AOS Microbio [9]: Neonatal sepsis question explicitly uses E. faecalis as a distractor vs GBS — the teaching point is that day-2 neonatal meningitis with G+ve cocci in chains = GBS, not Enterococcus.

  6. PD peritonitis [8]: Enterococcus is among G+ve organisms causing CAPD peritonitis; empirical Rx = cefazolin + amikacin; adjust after culture.

  • E. faecium vs E. faecalis: faecium is the "more resistant" species — more likely ampicillin-R and VRE. If a vignette says "ampicillin-resistant Enterococcus," think E. faecium first.
  • Enterococcus vs Streptococcus on Gram stain: both are G+ve cocci in chains. Bile-esculin +ve and growth in 6.5% NaCl clinch Enterococcus.
  • Cephalosporin trap: A patient on empirical ceftriaxone grows Enterococcus → treatment is failing because cephalosporins have no activity against Enterococcus. Must switch to ampicillin or vancomycin.
  • S. bovis vs Enterococcus in IE: Both are "Group D." S. bovis IE → colonoscopy (association with colon cancer). Enterococcal IE → look for GU/GI source of entry (instrumentation, catheterisation).
  • VRE significance: E. faecium with VanA phenotype = resistant to both vancomycin AND teicoplanin. Treatment options: linezolid, daptomycin. This is a notifiable multidrug-resistant organism in HK hospitals requiring contact isolation.

2023 Fourth Summative MCQ Q83 [10]:

"A neonate (day 2 of life) develops high fever, lethargy and feeding difficulty. Sepsis workup is performed including lumbar puncture. [Gram stain image of CSF shown.] Which of the following microorganisms is MOST LIKELY to be grown in culture from the cerebrospinal fluid? A. Enterococcus faecalis B. Group B streptococcus C. Staphylococcus aureus D. Streptococcus pneumoniae"

Correct answer: B. Group B streptococcus.

Rationale: Day 2 neonate = early-onset neonatal sepsis. G+ve cocci in chains on CSF Gram stain in this age group → GBS (S. agalactiae). E. faecalis (option A) is a deliberate distractor — also G+ve cocci in chains, but GBS is overwhelmingly the most common cause of early-onset neonatal meningitis. Key discriminator: clinical context (age < 7 days) overrides morphological similarity.

No other past paper questions in the indexed context directly test E. faecium specifically. However, IE and UTI questions frequently include Enterococcus as part of differential or treatment selection stems (e.g., "which antibiotic does NOT cover Enterococcus?" → answer: cephalosporin).

[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pp. 237, 240) — IE microbiology and management [2] Senior notes: Ryan Ho Cardiology.pdf (pp. 147, 149, 150) — IE microbiology, Duke criteria, and management [3] Lecture slides: GC 102. Fever after chemotherapy infections in immunocompromised hosts [Handout].pdf (p. 5) — device-related infections, Enterococcus in Foley catheter UTI [4] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 993) — Enterococcus intrinsic resistance, treatment [5] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 400) — Enterococcus intrinsic resistance, treatment [6] Senior notes: Ryan Ho Urogenital.pdf (pp. 123–124) — UTI microbiology tables [7] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 341) — UTI microbiology tables [8] Senior notes: Ryan Ho Urogenital.pdf (p. 114) — PD peritonitis microbiology and management [9] AOS material: AOS - Microbio.pdf (p. 3) — neonatal sepsis MCQ with E. faecalis as distractor [10] Past papers: 2023 Fourth Summative MCQ.pdf (p. 32) — Q83 neonatal meningitis

Enterococcus faecalis

Gram-positive, catalase-negative coccus found in chains, a leading cause of nosocomial urinary tract infections, endocarditis, and biliary tract infections, notable for intrinsic resistance to cephalosporins and low-level aminoglycosides.

Bacillus anthracis

Gram-positive, spore-forming, encapsulated, non-motile rod that causes anthrax, manifesting as cutaneous, inhalational, or gastrointestinal disease.

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