Highly penicillin-resistant strains of viridans group streptococci, nutritionally variant streptococci like Granulicatella sp., Gemella sp., Abiotrophia defectiva, and Enterococci are usually treated with a combination therapy consisting of penicillin and an aminoglycoside for the entire duration of 4–6 weeks.Some people may be treated with a relatively shorter course of treatment (two weeks) with benzyl penicillin IV if infection is caused by viridans group streptococci or Streptococcus bovis as long as the following conditions are met:

Endocarditis of a native valve, not of a prosthetic valve
A MIC ≤ 0.12 mg/l
A complication such as heart failure, arrhythmia, or pulmonary embolism occurs
No evidence of extracardiac complication like septic thromboembolism
No vegetations > 5 mm in diameter conduction defects
Rapid clinical response and clearance of bloodstream infectionAdditionally, oxacillin-susceptible Staphylococcus aureus native valve endocarditis of the right side can also be treated with a short 2-week course of a beta-lactam antibiotic such as nafcillin with or without aminoglycosides. The main indication for surgical treatment is regurgitation or stenosis. In active infective endocarditis, the surgery should remove enough leaflet tissue to ensure eradication of the infectious process. Subsequent valve repair can be performed in limited disease.
Due to delay in growth and identification in these cases, patients may be erroneously classified as "culture-negative" endocarditis. Heart side
Endocarditis can also be classified by the side of the heart affected:

People who intravenously inject opioids such as heroin or methamphetamine may introduce infection which can travel to the right side of the heart, classically affecting the tricuspid valve, and most often caused by S. aureus. Regardless of cause, left-sided endocarditis is more common in people who inject IV drugs and people who do not use substances than right-sided endocarditis. Infection setting
Another form of endocarditis is healthcare-associated endocarditis when the infecting organism is believed to be transmitted in a health care setting like hospital, dialysis unit or a residential nursing home. Nosocomial endocarditis is a form of healthcare associated endocarditis in which the infective organism is acquired during a stay in a hospital and it is usually secondary to presence of intravenous catheters, total parenteral nutrition lines, pacemakers, etc. Valve type
Finally, the distinction between native-valve endocarditis and prosthetic-valve endocarditis is clinically important. Prosthetic valve endocarditis can be early (< 60 days of valvular surgery), intermediate (60 days to 1 year) or late (> 1 year following valvular surgery). Early prosthetic valve endocarditis is usually due to intraoperative contamination or postoperative bacterial contamination which is usually nosocomial in nature. Late prosthetic valve endocarditis is usually due to community-acquired microorganisms.Prosthetic valve endocarditis is commonly caused by Staphylococcus epidermidis as it is capable of growing as a biofilm on plastic surfaces.