Rare cause of infective endocarditis

Shadiya Sulthana S¹, S Aravindakumar², Thilagavathy³

¹PG Resident – Internal Medicine, Kauvery Hospitals, Trichy, Tamil Nadu

²Consultant Interventional Cardiologist, Kauvery Hospital, Heart City, Trichy, Tamil Nadu

³Consultant Microbiologist, Kauvery Hospital, Cantonment, Trichy, Tamil Nadu

Introduction

Abiotrophia defectiva is a nutritionally deficient streptococcus that eludes detection on conventional culture media, often complicating clinical diagnosis. Despite its slow and demanding growth, it exhibits marked virulence, particularly targeting the heart’s endovascular surfaces. It is a notable cause of culture-negative infective endocarditis and is distinguished by its aggressive course, frequently resulting in severe valvular damage, congestive heart failure, and a high risk of systemic embolization. Furthermore, its intrinsic resistance to several standard antimicrobial agents contributes to poor clinical outcomes, making early recognition and appropriate therapy crucial for effective management.

Case Presentation

A 35-year-old gentleman with no known comorbidities, but with a history of chronic alcohol use, presented with a two-month history of fever, anorexia, and significant weight loss. He also reported palpitations and exertional dyspnea consistent with New York Heart Association (NYHA) class II symptoms.

Initial evaluation at an outside facility included transthoracic echocardiography, which revealed mitral valve prolapse involving both the anterior and posterior leaflets. He subsequently presented to our center for further evaluation. Notably, he reported undergoing a dental extraction approximately eight months prior.

Given the clinical picture, infective endocarditis was suspected, and a transesophageal echocardiogram (TEE) was performed. TEE revealed vegetations on both the anterior and posterior mitral valve leaflets. Blood cultures were obtained from three separate sites. Gram staining demonstrated gram-negative bacilli, raising suspicion for organisms within the HACEK group.

However, cultures later revealed Streptococcus-like colonies on blood agar. To confirm the identity of the organism, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was performed, which identified Abiotrophia defectiva. Antibiotic susceptibility testing showed the organism was pan-sensitive to ceftriaxone and gentamicin. Accordingly, the patient was started on ceftriaxone and amikacin.

Gram Stain

Fig (1): Gram negative bacilli visualised

Transesophageal Echo

Discussion

Nutritionally variant streptococci (NVS), first described in 1961, are part of the normal oral, intestinal, and genitourinary flora, and have occasionally been isolated from blood
One notable subspecies, Abiotrophia defectiva, is an uncommon but recognized cause of infective endocarditis (IE), as well as other serious infections such as brain abscesses, osteomyelitis, and septic arthritis. Colonization rates in healthy individuals have been reported as high as 11.8%.
Abiotrophia species are characterized by satellite colony growth and fastidious nutritional requirements. Although they can grow on standard media, supplementation with vitamin B6 or cysteine enhances selective isolation.
In routine cultures, these bacteria may be missed due to nutrient limitations or overgrowth by other organisms. However, with advances in microbiology and updated isolation techniques, detection has improved. In our case, positive blood cultures facilitated timely diagnosis and targeted therapy.
Abiotrophia and Granulicatella species are rare causes of IE but have been shown to be more prevalent than the combined HACEK organisms (1.51% vs. 0.88%).
Patients with Abiotrophia endocarditis tend to be younger—by about two decades—than those with viridans group streptococci (VGS) IE, with a mean age of 42 years.
Dental procedures, particularly within three months of presentation, are implicated in roughly 32% of cases, raising the question of prophylactic antibiotics in this population.
The mitral valve is most commonly affected; though aortic involvement has been noted.
Intravenous drug use is less commonly associated with Abiotrophia endocarditis compared to VGS endocarditis. Our patient had no history of drug use but had undergone a dental extraction eight months prior to presentation.
Historically thought to have a higher mortality than VGS endocarditis, more recent analyses show comparable mortality rates (9.2% vs. 9.6%).
However, Abiotrophia infections are associated with a higher incidence of periannular complications (28.9% vs. 22%) and a greater need for surgical intervention (65.8% vs. 50%, p=0.003) , although there is no increased predilection for prosthetic valve involvement.
Bouvet et al. demonstrated superior efficacy of combination therapy with penicillin and gentamicin over penicillin monotherapy in non-VGS streptococcal endocarditis.
Vancomycin was found to be equally effective, supporting its use in penicillin-allergic patients.
Current AHA guidelines recommend a 4–6-week course of penicillin G plus gentamicin, with vancomycin as an alternative. Notably, rising resistance to beta-lactams, macrolides, and penicillins has been documented.
Our patient was initiated on ceftriaxone and amikacin.

Conclusion

Abiotrophia defectiva is a rare cause of infective endocarditis with few cases reported worldwide. It is a slow growing, highly fastidious organisms which is difficult to grow in routine culture media.

Interestingly, our patient’s initial blood cultures revealed colonies with streptococcal morphology, prompting further identification using MALDI-TOF mass spectrometry, which confirmed the presence of Abiotrophia defectiva.

It is important to consider this rare cause, particularly in culture negative infective endocarditis to prevent complications and early initiation of treatment.

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Rare cause of infective endocarditis