**6. Treatment**

Antimicrobial susceptibility testing is very difficult for *Abiotrophia* and *Granulicatella* due to their fastidious nature. In addition, the results of susceptibility testing may not be accurate or reliable. Microbiological cure is difficult and infective endocarditis caused by these organisms is associated with high rates of treatment failures. Therefore, AHA (American Heart Association) and British Society for Antimicrobial Chemotherapy (BSAC) Infective Endocarditis treatment guideline for *Abiotrophia defectiva* and *Granulicatella* species is very similar to treatment guidelines for enterococcal endocarditis [33, 56].

Recommended treatment regimen is Ampicillin (12 g/d in divided doses) or penicillin (18–30 million U/D in divided doses or by continuous infusion) plus gentamicin 3 mg/kg/d in 2–3 divided doses).

For those patients who are intolerant to penicillin, Vancomycin alone without the use of gentamicin can be given for therapy. This is in contrast to enterococcal endocarditis treatment where Vancomycin is combined with gentamicin [33].

The duration of treatment for *Abiotrophia* or *Granulicatella* endocarditis needs to be determined by consultation with an infectious disease expert. As a general guidance, AHA recommendations for treatment durations for enterococcal endocarditis are as follows:

The treatment duration is 4 weeks for native valve endocarditis with symptoms or illness ≤3 months. 6 week therapy is recommended for patients with symptoms >3 months. For prosthetic valve or other prosthetic cardiac material infections, minimum 6 weeks of antibiotic therapy is recommended [33].

Historically, in animal models it was shown that Penicillin alone was inferior to Penicillin plus aminoglycoside or Vancomycin alone for the treatment of infective endocarditis caused by NVS [57, 58]. it was shown that penicillin plus low dose (0.32 mg/kg) vs. high dose (1.05 mg/kg) gentamicin treatment results were virtually identical [57].

There is encouraging data to suggest that shortened courses of aminoglycosides in the treatment regimens (median 15 days) may result is similar clinical outcomes in treatment of enterococcal endocarditis. However this particular issue requires further study and it is not yet known how this would apply to treatment of infective endocarditis caused by *Abiotrophia defectiva* or *Granulicatella* species. [49].

Given the growing concerns over antibiotic resistance among NVS, poor treatment outcomes and high rates of treatment failures it is important to look into data for susceptibilities of a broad range of antibiotics. There is however limited data available regarding the antibiotic susceptibilities of *Granulicatella* and *Abiotrophias* spp. due to the rare nature of the infections, the specific nutritional growth requirements and difficulties in standardization of testing methodologies.
