Morphology: Alpha-hemolytic streptococci, optochin-resistant (distinguishes from pneumococcus), bile-insoluble. Heterogeneous group: mitis group (S. mitis, S. sanguinis, S. oralis, S. gordonii), anginosus group (S. anginosus, S. intermedius, S. constellatus), mutans group, salivarius group.
Typical drugs
- #1Penicillin G— Penicillin-susceptible VGS endocarditis (MIC ≤0.12) — 4-week monotherapy or 2-week combo with gentamicin.
- #2Ceftriaxone— OPAT-friendly equivalent to PCN for susceptible VGS IE — once-daily dosing.
- #3Vancomycin— PCN-resistant strains (MIC ≥0.5) or true PCN allergy.
- #4Ampicillin-sulbactam— Anginosus group abscesses (often anaerobic + microaerophilic mix).
Empiric therapy when resistant
For VGS IE with PCN MIC 0.12–0.5: PCN or CTX plus gentamicin × 2 weeks for first 2 weeks. MIC >0.5 or true PCN allergy → vancomycin × 4 weeks (6 weeks for prosthetic valve).
Resistance mechanisms
altered-target
Altered PBPs — penicillin MIC creep, especially mitis group
Example: 20–30% of VGS isolates now have MIC >0.12 (intermediate or resistant). MUST get MIC for IE — drives whether monotherapy or combo therapy and whether ceftriaxone vs vanc.
Resistance notes
Always request MIC for IE isolates — drives regimen choice. Macrolide and clindamycin resistance rising in some regions.
Common syndromes
Pearls
Most common cause of native-valve subacute endocarditis — classic indolent IE in patient with prior valve disease and dental work. Anginosus group (S. anginosus / intermedius / constellatus) is the exception — these form abscesses (brain, liver, lung, dental) rather than IE; treat aggressively with drainage + β-lactam + metronidazole-grade anaerobe coverage. S. gallolyticus (formerly S. bovis) IE → colonoscopy to rule out colorectal CA. Dental procedure prophylaxis controversial; AHA 2021 recommends only for highest-risk cardiac lesions.
References
- AHA Infective Endocarditis Guidelines (2015)
- ESC Endocarditis Guidelines (2023)