Abstract

Introduction: Among streptococcus species, Abiotrophia defectiva (A. Defectiva) is a subspecies with strict growth requirements and is specifically designated as a Nutritional Variant Streptococcus (NVS). The special growth factors utilized by these bacteria are for cell wall synthesis and replication. These bacteria are normal commensals of the oral, gastrointestinal, and genitourinary tract. Against the backdrop of specific risk factors, these bacteria can enter the bloodstream, thereby opening the door to systemic infections, including endocarditis.
Clinical case: 75-year-old female with a PMH of AFIB [Atrial Fibrillation], atrial flutter, TAVR [Transaortic valve replacement], HTN [Hypertension], CVA [Cerebrovascular accident], and HLD [Hyperlipidemia] presented with left MCA [Middle Cerebral Artery Occlusion] occlusion, which was successfully treated with embolectomy. She was eventually discharged but returned 1 week later with shortness of breath. Evaluation revealed elevated troponin levels and pulmonary edema, necessitating a cardiology consult for possible cardiac catheterization. Routine workups, including bacterial cultures, revealed bacteremia. Echocardiography was considered because of bacteremia in the context of TAVR. The TEE showed large mobile vegetations in the aortic valve, the largest being 1.5x1.0cm. Repeated blood culture later grew A. defectiva, thus confirming the diagnosis of NVS provoked endocarditis. Considering the infection with A. Defectiva, IV [intravenous] Amipicillin-Sulbactam for 6 weeks, was recommended by the Infectious Disease Team. Cardiothoracic surgery was also consulted for possible surgical intervention. Long-term antibiotic clinical suppression is recommended given the high relapse rate seen in these cases.
Conclusion: By presenting this clinical case, we would like to emphasize the clinical relevance of A. Defectiva-induced endocarditis in patients with relevant risk factors. Well-honed clinical intuition and a high degree of preconception are almost always necessary for early diagnosis of this rare endocarditis. A delayed diagnosis is likely, given the strict growth requirements and the protracted clinical course. Despite antibiotic administration, a successful therapeutic response is stonewalled by antibiotic resistance and a higher relapse rate. On grounds of this, rapid clinical progression, and valvular complications command surgical management, thereby triggering amplified mortality and morbidity.

Keywords: Nutritionally variant streptococci; Heart disease; Endocarditis; Vegetations; Septic embolism; Stroke; Osteomyelitis; Brain abscesses

Abbreviations: A. Defectiva: Abiotrophia Defectiva; NVS: Nutritionally Variant Streptococcus; PMH: Past Medical History; AFIB: Atrial Fibrillation; TAVR: Transaortic Valve Replacement; HTN: Hypertension; CVA: Cerebrovascular Accident; HLD: Hyperlipidemia; MCA: Middle Cerebral Artery; TEE: Transesophageal Echocardiography; NSTEMI: Non-ST Elevation Myocardial Infarction; EF: Ejection Fraction; AI: Aortic Incompetence; IV: Intravenous; 16S rRNA: 16 Svedberg Units Ribosomal Ribonucleic Acid; B6: Pyridoxine; IE: Infective Endocarditis; MALTI-TOF-MS: Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry; mNGS: Megagenomic Next-Generation Sequencing; PCR-RFL: Polymerase Chain Reaction-Restriction Length Polymorphism; Cath Lab: Cardiac Catheterization Laboratory