No, Enterococcus is NOT the same as Streptococcus
Enterococcus and Streptococcus are distinct genera of bacteria, though they are closely related and were historically classified together. Enterococci were previously considered part of the genus Streptococcus but have been reclassified into their own separate genus 1, 2.
Key Taxonomic Distinction
The organisms were separated based on phylogenetic analysis showing they form distinct evolutionary clusters within the catalase-negative gram-positive cocci 3. While both belong to the same broad family of bacteria, they have sufficient genetic and phenotypic differences to warrant separate classification 2.
Critical Clinical Differences
The distinction between these genera has major implications for treatment:
Antibiotic Susceptibility Patterns
Enterococci are inherently more resistant to antibiotics than streptococci 4:
- Streptococci (including viridans group streptococci and β-hemolytic streptococci) are typically killed by monotherapy with penicillin, ampicillin, or vancomycin
- Enterococci are only inhibited but not killed by these same antibiotics when used alone
Treatment Requirements
For serious infections like endocarditis 4:
- Streptococcal endocarditis: Can often be treated with single-drug therapy (penicillin or ceftriaxone)
- Enterococcal endocarditis: Requires combination therapy with a cell wall-active agent (penicillin, ampicillin, or vancomycin) PLUS an aminoglycoside (gentamicin or streptomycin) to achieve bactericidal synergy
Resistance Profiles
Enterococci possess numerous inherent resistance traits that streptococci lack 1:
- Intrinsic resistance to cephalosporins (all generations)
- Resistance to clindamycin
- Resistance to penicillinase-resistant penicillins (oxacillin, nafcillin)
- Potential for high-level aminoglycoside resistance
- Emerging vancomycin resistance
Clinical Pitfall
Do not assume streptococcal treatment regimens will work for enterococcal infections. The most common error is treating enterococcal endocarditis with monotherapy or using cephalosporins, which are completely ineffective against enterococci despite working well for many streptococcal infections.