Enterococcus faecalis

# Overview
Enterococcus faecalis is a Gram-positive commensal bacterium inhabiting the gastrointestinal tracts of humans and other mammals. Like other species in the genus Enterococcus, E. faecalis can cause life-threatening infections in humans, especially in the nosocomial (hospital) environment: the naturally high levels of antibiotic resistance found in E. faecalis contribute to its pathogenicity.

# Pathogenesis
E. faecalis can cause endocarditis, as well as bladder, prostate, and epididymal infections; nervous system infections are less common.
E. faecalis is resistant to many commonly used antimicrobial agents (aminoglycosides, aztreonam, cephalosporins, clindamycin, the semi-synthetic penicillins nafcillin and oxacillin, and trimethoprim-sulfamethoxazole). Exposure to cephalosporins is a particularly important risk factor for colonization and infection with enterococci.

# Historical Perspective
Prior to 1984, enterococci were members of the genus Streptococcus: thus E. faecalis was known as Streptococcus faecalis.

# Treatment

## Antimicrobial Regimen
- 1. Bacteremia
- 1.1 Ampicillin or penicillin susceptible
- Preferred regimen (1): Ampicillin 2 g IV q4-6h
- Preferred regimen (2): Ampicillin 2 g IV q4-6h AND Gentamicin 1 mg/kg IV/IM q8h
- 1.2 Ampicillin resistant and vancomycin susceptible or penicillin allergy
- Preferred regimen (1): Vancomycin 15 mg/kg IV q12h AND Gentamicin 1 mg/kg IV/IM q8h
- Preferred regimen (2): Linezolid 600 mg IV q12h
- Preferred regimen (3): Daptomycin 6 mg/kg IV q24h
- 1.3 Ampicillin and vancomycin resistant
- Preferred regimen (1): Linezolid 600 mg IV q12h
- Preferred regimen (2): Daptomycin 6 mg/kg IV q24h
- 2. Endocarditis
- 2.1 Endocarditis in adults
- 2.1.1 Strains susceptible to penicillin, gentamicin, and vancomycin
- Preferred regimen: (Ampicillin 12 g IV q24h for 46 weeks OR Aqueous crystalline penicillin G sodium 1830 MU IV q24h for 46 weeks) AND Gentamicin sulfate 3 mg/kg IV/IM q24h for 46 weeks
- Alternative regimen: Vancomycin hydrochloride 30 mg/kg IV q24h for 6 weeks AND Gentamicin sulfate 3 mg/kg IV/IM q24h for 6 weeks
- Note (1): In case of native valve endocarditis with symptoms  3 months, a 4-week course of therapy is recommended.
- Note (2): In case of native valve endocarditis with symptoms > 3 months, a 6-week course of therapy is recommended.
- Note (3): In case of prosthetic valve or other prosthetic cardiac material, a minimum of 6-week course of therapy is recommended.
- 2.1.2 Strains susceptible to penicillin, streptomycin, and vancomycin and resistant to gentamicin
- Preferred regimen: (Ampicillin 12 g IV q24h for 46 weeks OR Aqueous crystalline penicillin G sodium 24 MU IV q24h for 46 weeks) AND Streptomycin sulfate 15 mg/kg IV/IM q24h for 46 weeks
- Alternate regimen: Vancomycin hydrochloride 30 mg/kg IV q24h  for 6 weeks AND Streptomycin sulfate 15 mg/kg IV/IM q24h for 6 weeks
- 2.1.3 Strains resistant to penicillin and susceptible to aminoglycoside and vancomycin
- 2.1.3.1  Lactamaseproducing strain
- Preferred regimen: Ampicillin-sulbactam 12 g IV q24h for 6 weeks AND Gentamicin sulfate 3 mg/kg IV/IM q24h 6 weeks
- Alternate regimen: Vancomycin hydrochloride 30 mg/kg IV q24h for 6 weeks AND Gentamicin sulfate 3 mg/kg IV/IM q24h for 6 weeks
- 2.1.3.2 Intrinsic penicillin resistance
- Preferred regimen: Vancomycin hydrochloride 30 mg/kg IV q24h for 6 weeks AND Gentamicin sulfate 3 mg/kg IV/IM q24h for 6 weeks
- 2.1.4 Strains resistant to penicillin, aminoglycoside, and vancomycin
- Preferred regimen (1): (Imipenem OR Cilastatin 2 g/day IV for  8weeks) AND Ampicillin 12 g/day IV for  8 weeks
- Preferred regimen (2): Ceftriaxone sodium 4 g IV/IM q24h for  8weeks AND Ampicillin 12 g IV q24h for  8 weeks
- 2.2 Endocarditis in pediatrics
- 2.2.1 Strains susceptible to penicillin, gentamicin, and vancomycin
- Preferred regimen: (Ampicillin 300 mg/kg IV q24h for 46 weeks OR Penicillin 0.3 MU/kg IV q24h for 46 weeks) AND Gentamicin 3 mg/kg IV/IM q24h 46 weeks
- Note (1): In case of native valve endocarditis with symptoms  3 months, a 4-week course of therapy is recommended.
- Note (2): In case of native valve endocarditis with symptoms > 3 months, a 6-week course of therapy is recommended.
- Note (3): In case of prosthetic valve or other prosthetic cardiac material, a minimum of 6-week course of therapy is recommended.
- Alternate regimen : Vancomycin 40 mg/kg IV q24h for 6 weeks AND Gentamicin 3 mg/kg IV/IM q24h for 6 weeks
- 2.2.2 Strains susceptible to penicillin, streptomycin, and vancomycin and resistant to gentamicin
- Preferred regimen: (Ampicillin 300 mg/kg IV q24h for 46 weeks OR Penicillin 0.3 MU/kg IV q24h for 46 weeks) AND Streptomycin 2030 mg/kg IV/IM q24h for 46 weeks
- Alternate regimen: Vancomycin hydrochloride 40 mg/kg IV q24h for 6 weeks AND Streptomycin sulfate 15 mg/kg IV/IM q24h for 6 weeks
- 2.2.3 Strains resistant to penicillin and susceptible to aminoglycoside and vancomycin
- 2.2.3.1  Lactamaseproducing strain
- Preferred regimen: Ampicillin-sulbactam 300 mg/kg IV q24h for 6 weeks AND Gentamicin 3 mg/kg IV/IM q24h for 6 weeks
- Alternate regimen: Vancomycin 40 mg/kg IV q24h for 6 weeks AND Gentamicin 3 mg/kg IV/IM q24h for 6 weeks
- 2.2.3.2 Intrinsic penicillin resistance
- Preferred regimen: Vancomycin 40 mg/kg IV q24h AND Gentamicin 3 mg/kg IV/IM q24h for 6 weeks
- 2.2.4 Strains resistant to penicillin, aminoglycoside, and vancomycin
- Preferred regimen: Imipenem/Cilastatin 60100 mg/kg IV q24h for  8 weeks AND Ampicillin 300 mg/kg IV q24h for  8 weeks
- Alternate regimen: Ceftriaxone 100 mg/kg IV/IM q24h AND Ampicillin 300 mg/kg IV q24h for  8 weeks
- 3. Meningitis
- 3.1 Ampicillin susceptible
- Preferred regimen: Ampicillin 12 g/day IV q4h AND Gentamicin 5 mg/kg/day IV q8h
- 3.2 Ampicillin resistant
- Preferred regimen: Vancomycin 3045 mg/kg/day IV q812h AND Gentamicin 5 mg/kg/day IV q8h
- 3.3 Ampicillin and vancomycin resistant
- Preferred regimen: Linezolid 600 mg IV q12h
- 4. Urinary tract infections 
- Preferred regimen (1): Nitrofurantoin 100 mg PO q6h for 5 days
- Preferred regimen (2): Fosfomycin 3 g PO single dose
- Preferred regimen (3): Amoxicillin 875 mg to 1 g PO q12h for 5 days
- 5. Intra abdominal or wound infections 
- Preferred regimen (1): Penicillin
- Preferred regimen (2): Ampicillin
- Alternative regimen (Penicillin allergy or high-level Penicillin resistance): Vancomycin
- Alternative regimen (For complicated skin-skin structure and intra-abdominal infection): Tigecycline 100 mg IV single dose and 50 mg IV q12h

# Gallery
- SEM depicts a small group of Gram-positive Enterococcus faecalis bacteria. From Public Health Image Library (PHIL). 
- Enterococcus faecalis cultured on an agar plate, testing for drug sensitivity in an anaerobic environment. From Public Health Image Library (PHIL). 
- SEM depicts Gram-positive Enterococcus faecalis sp. bacteria. From Public Health Image Library (PHIL). 
- Quantitative difference in hemolytic reactivity seen on BAP with group-D Streptococci (left wedge), group-B Streptococci (middle wedge), and group-A Streptococci (right wedge) bacteria.  From Public Health Image Library (PHIL).