Infective endocarditis due to Abiotrophia defectiva and Granulicatella spp. complicated by infectious intracranial cerebral aneurysms: a report of three cases and review of the literature

Secretome analysis and virulence assessment in Abiotrophia defectiva

Background

Abiotrophia defectiva, although infrequently occurring, is a notable cause of culture-negative infective endocarditis with limited research on its virulence. Associated with oral infections such as dental caries, exploring its secretome may provide insights into virulence mechanisms. Our study aimed to analyze and characterize the secretome of A. defectiva strain CCUG 27639.

Methods

Secretome of A. defectiva was prepared from broth cultures and subjected to mass spectrometry and proteomics for protein identification. Inflammatory potential of the secretome was assessed by ELISA.

Results

Eighty-four proteins were identified, with diverse subcellular localizations predicted by PSORTb. Notably, 20 were cytoplasmic, 12 cytoplasmic membrane, 5 extracellular, and 9 cell wall-anchored proteins. Bioinformatics tools revealed 54 proteins secreted via the 'Sec' pathway and 8 via a non-classical pathway. Moonlighting functions were found in 23 proteins, with over 20 exhibiting potential virulence properties, including peroxiredoxin and oligopeptide ABC transporter substrate-binding protein. Gene Ontology and KEGG analyses categorized protein sequences in various pathways. STRING analysis revealed functional protein association networks. Cytokine profiling demonstrated significant proinflammatory cytokine release (IL-8, IL-1β, and CCL5) from human PBMCs.

Conclusions

Our study provides a comprehensive understanding of A. defectiva's secretome, laying the foundation for insights into its pathogenicity.

Delayed formation and rupture of intracranial aneurysm following Abiotrophia defectiva endocarditis

Abiotrophia defectiva is a type of Streptococci and is a rare cause of infectious endocarditis. The progression and outcomes of infectious intracranial aneurysms (IIAs) associated with this species are unknown due to a limited number of reported cases. A woman in her 20s with a sudden headache had a subarachnoid haemorrhage on a head CT scan. Cerebral angiography showed an aneurysm on the right middle cerebral artery. She was diagnosed with infectious endocarditis caused by A. defectiva and underwent parent artery occlusion. Despite initiating targeted antibiotic therapy, a new IIA developed and ruptured 14 days postadmission. A second parent artery occlusion was performed on the new IIA. Following 6 weeks of continued antibiotic therapy, she underwent mitral valve repair and was discharged with no neurological symptoms. Endocarditis caused by A. defectiva can lead to the delayed formation of an IIA. Endovascular treatment was effective for repeated ruptured IIAs.

Association of infective endocarditis caused by Abiotrophia defectiva with mycotic aneurysm formation: A case report and the review of the literature

A 74-year-old woman with a history of mitral valve prolapse with mitral regurgitation was transferred to our hospital due to infective endocarditis. Blood culture revealed Abiotrophia defectiva which is known as a nutritional variant streptococcus. Transesophageal echocardiography revealed posterior leaflet (P2) prolapse due to rupture of tendon chordae with severe mitral regurgitation and vegetation on posterior leaflet. Magnetic resonance imaging (MRI) revealed multiple infarction lesions in left temporal lobe and parietal lobe and mycotic aneurysm formation of right middle cerebral artery. Because A. defectiva cannot be cultured on non-supplemented media, their prevalence may be underreported.

Learning objective

A number of causative microorganisms of infective endocarditis have been identified. Streptococci and staphylococci account for 80 % of cases of infective endocarditis. Abiotrophia defectiva does not grow in ordinary growth media and its prevalence may be underreported. It is important to know A. defectiva causes infective endocarditis with mycotic aneurysm formation.

Clostridium Tetani Bacteremia From a Suspected Cutaneous Source

Bacteremia is a rare complication of Clostridium tetani infection. To our knowledge, there are only two case reports to date of C. tetani bacteremia, both hypothesized to be secondary to a gastrointestinal source. Herein, we report a case of an elderly man with genome sequence-proven C. tetani bacteremia from a possible cutaneous source without neuromuscular symptoms.

Infective endocarditis by a rare and fastidious agent: Abiotrophia defectiva

Abiotrophia defectiva is a nutritional variant streptococcus, with affinity for endovascular structures that cannot be cultured on non-supplemented media, leading to a delay in diagnosis. This case describes a 36-year-old woman with a previously known bicuspid aortic valve that presented with asthenia, myalgias and anorexia with 2-month onset. On admission, we documented fever and a systolic murmur. Transthoracic echocardiography revealed an oscillating mass attached to the aortic valve. The patient was admitted with a possible diagnosis of infective endocarditis. Later, blood cultures were positive for A. defectiva Due to severe aortic regurgitation and congestive heart failure, she underwent surgical aortic valve replacement. After 6 weeks of antimicrobial therapy, the patient experienced full recovery. Despite of its rarity, A. defectiva endocarditis is associated with significant morbidity with mortality and physicians must have a high level of suspicion to ensure a prompt diagnosis and provide the appropriate treatment.

Mitral Valve Subacute Endocarditis Caused by Abiotrophia Defectiva: A Case Report

Abiotrophia defectiva is a rare agent of endocarditis and subacute presentation may delay the diagnosis. We present the case of a 41-year-old male who was admitted to the hospital for further investigation regarding a consumptive syndrome with microcytic anaemia. Past medical history included new-onset mitral insufficiency followed by an ischaemic stroke due to small vessel disease. Thoraco-abdominal computed tomography revealed a splenic infarction. In the presence of two ischaemic events associated with mitral valve disease of unknown aetiology, we considered the possibility of subacute endocarditis. Blood cultures were positive for Abiotrophia defectiva, and transoesophageal echocardiography confirmed the diagnosis. As a subacute presentation of endocarditis, the paucity of symptoms caused a five-month delay in diagnosis. New-onset valvular disease and a stroke in an otherwise healthy young patient should always prompt proper investigation. This case highlights several complications caused by septic emboli of undiagnosed and untreated endocarditis.

Challenges in the diagnosis and management of Granulicatella elegans endocarditis in a 9-year-old child

A 9-year-old child, with a background of repaired pulmonary atresia and Ebstein's anomaly, presented with fever, night sweats and lethargy. Blood cultures grew Granulicatella elegans, a nutritionally variant Streptococcus and known cause of infective endocarditis (IE). Echocardiogram revealed no clear vegetation, but increased stenosis of the right ventricle to pulmonary artery conduit. The child was successfully managed with high-dose benzylpenicillin, completing 2 weeks in the hospital, and was discharged to complete the final 4 weeks of therapy with ceftriaxone in the community, as per European Society of Cardiology guidance. IE caused by any Granulicatella species is rare, with infection due to G. elegans rarer still. It is a Gram-positive bacteria that presents a diagnostic challenge due to non-specific symptoms at presentation and difficulty in growing the organism on culture medium. We present a case of G. elegans endocarditis in a young child, which illustrates the challenges in managing this condition and the importance of considering atypical organism endocarditis in children presenting with fever of unknown origin, in particular those with a background of congenital cardiac disease. We review the literature on Granulicatella endocarditis, and briefly discuss the challenges of managing this condition in a child with an autism spectrum disorder and learning difficulties.

Streptobacillus moniliformis With Features of Hemophagocytic Lymphohistiocytosis Identified by Direct Sequencing

Rat-bite fever caused by Streptobacillus moniliformis is a rare infection that may be fatal. An adolescent male presented with multiorgan failure, negative blood cultures and Gram-negative rods in blood smear. S. moniliformis was identified by 16S ribosomal RNA gene sequencing from the blood. He developed systemic hyperinflammatory syndrome resembling hemophagocytic lymphohistiocytosis, for which immune-globulins and steroids were added to the antibiotic regimen and he rapidly recovered.

Infective endocarditis caused by Abiotrophia defectiva presenting as anterior mitral leaflet perforation mimicking cleft anterior mitral leaflet

Infective endocarditis (IE) is primarily a bacterial infection of the heart valves. The most common organisms implicated include Staphylococcus and Streptococcus species. However, with the advent of MALDI-TOF and molecular techniques, the reports of IE being caused by rare organisms are on a rise. Here we describe a case of IE due to Abiotrophia defectiva. This is the first report of simultaneous infection of both mitral and aortic valves by Abiotrophia defectiva from India. IE caused by Abiotrophia defectiva has been seen to be more severe, associated with higher failure rates and relapse. This emphasizes the accurate identification of nutritionally variant Streptococcus (NVS) species as the management of choice varies between Abiotrophia and Granulicatella.

Development of a periprosthetic joint infection by Abiotrophia defectiva years after total knee arthroplasty

A 74-year-old male presented with acute right knee pain and inability to ambulate. The patient had a total knee arthroplasty, previously complicated by a periprosthetic femur fracture requiring surgical fixation and subsequent methicillin-resistant Staphylococcus epidermidis periprosthetic joint infection treated via two-stage revision. Cultures from knee fluid aspiration were positive for Abiotrophia defectiva. Identification was confirmed using matrix-assisted laser desorption ionization–time of flight mass spectrometry. The patient underwent a two-stage revision. Between stages, the patient received intravenous ceftriaxone for six weeks with subsequent normalization of inflammatory markers. Diagnosis of periprosthetic joint infection with identification of the organism is important to guide appropriate treatment.