52-year-old healthy female presents to the hospital for 3 weeks of intermittent fever and progressive dyspnea on exertion. History only notable for multiple dental procedures in recent months.
Exam demonstrates new diastolic murmur, rales in the lung bases, and lower extremity edema. Echocardiogram reveals a large mitral vegetation.
Blood cultures are obtained and return positive in 72 hours with a morphology of gram-positive cocci in chains. This is streaked on blood agar plate but only grows in the presence of Staphylococcus aureus as pictured.
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Correct Answer: Ampicillin plus gentamicin
This case emphasizes empiric treatment of nutritional variant streptococci (NVS) endocarditis with combination of ampicillin and gentamicin.
This case describes patient with several findings concerning for endocarditis and vegetation confirmed on MV.
The pathogen is a NVS, as evidenced by its ability to only grow in the presence of another organism (satellite growth). These organisms require thiol compounds to grow, which are not present on traditional agar. We now often identify these pathogens at the species level, Abiotrophia and Granulicatella. Poor dentition is an additional clue.
If the organism is identified as being penicillin sensitive (MIC < 0.5 ug/mL), penicillin or ampicillin monotherapy is preferred. When MIC is ≥ 0.5 ug/mL or when the susceptibility is not known, guideline recommended treatment is ampicillin or penicillin for 4 weeks plus gentamicin for 2 weeks.
Distractor answer choices
- NVS variable susceptibility to ceftriaxone, and this is not recommended unless susceptibility is confirmed.
- Vancomycin is only indicated in patients who are intolerant of penicillins
- Ampicillin plus ceftriaxone has data for synergystic use in susceptible Enterococcus endocarditis.
- Vancomycin plus rifampin plus gentamicin may be considered in prosthetic valve endocarditis from staph aureus
- We had to share this chart from a recent open access publication in Circulation describing the prevalence of endocarditis amongst various strep species (linked below). A good reminder of how diverse this group of bacteria are! Note our friend Granulicatella, low frequency but moderate risk of infective endocarditis.
Links:
A Must-Read Article for all ID fellows about streptococcal species and endocarditis.
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This question was uploaded on 4/4/22
Author Nathan Nolan at Washington University