Neisseria elongata prosthetic valve endocarditis : case report and literature review

Case Presentation: A 55-year-old Taiwanese man with history of Streptococcus viridans endocarditis status post prosthetic mitral and aortic valve replacements presented with a 2-week history of progressive fatigue and altered mental status. He presented with fever, lethargy and shock. He was intubated and started on vasopressors. A systolic murmur was noted with leukocytosis and acute renal failure. He was started on broad-spectrum antibiotics. An initial trans-oesophageal echocardiogram (TOE) did not reveal vegetation, but showed an elevated aortic valve gradient of 70 mmHg consistent with severe aortic stenosis. A repeat TOE revealed multiple mobile and immobile mitral and aortic valve vegetations with an abscess extending toward the aortic valve. Three sets of positive blood cultures from admission identified N. elongata. Antibiotics were tailored to ceftriaxone. He underwent urgent aortic and mitral valve replacement. He completed a 6-week course of ceftriaxone. At discharge, twodimensional echo revealed normal heart function with normal prosthetic mitral and aortic valves.


Introduction
Neisseria elongata, a Gram-variable, rod-shaped member of the family Neisseriaceae, is a constituent of the normal human oropharyngeal flora (Grant et al., 1990;Haddow et al., 2004).It was previously thought to be non-pathogenic, but became increasingly recognized as a rare cause of infective endocarditis as well as osteomyelitis.It causes an acute, destructive endocarditis.Here, to the best of our knowledge, we describe the first case of bivalvular prosthetic valve endocarditis due to N. elongata.

Case report
A 55-year-old Taiwanese man with a history of Streptococcus viridans endocarditis status post prosthetic mitral and aortic valve replacements in 1999, with recurrent S. viridans endocarditis, presented with a 2-week history of progressive generalized weakness and altered mental status.He had a dental crown placed 3-4 months prior to admission without prophylactic antibiotics.
He presented to an outside emergency department with fever of 102 uF (39 uC) and shock.He was intubated and started on vasopressors.A systolic murmur was noted on exam.He was found to have marked leukocytosis (white blood cells 69 K/mcL with 17 % bands), thrombocytopenia (platelets 22 K/mcL), lactic acidosis (lactate 5.9 mg dl) and acute renal failure.He was admitted to the intensive care unit, and started on vancomycin, cefepime, ampicillin and gentamicin.

Investigations
An initial trans-esophageal echocardiogram (TEE) did not reveal any vegetation, but showed an elevated aortic valve gradient of 70 mmHg consistent with severe aortic stenosis.He was transferred to our institution for further management of his septic shock and severe aortic stenosis, with presumed endocarditis.
Given the strong clinical suspicion for endocarditis and the concern that the initial TEE may have been misinterpreted due to the presence of prosthetic valves, the TEE was repeated.The repeated TEE revealed multiple mobile and immobile mitral valve vegetations with abscess extending toward the aortic valve (Fig. 1), and several small, mobile aortic valve vegetations.
A magnetic resonance imaging scan of the brain revealed multiple diffuse septic emboli.A computed tomography scan of the abdomen/pelvis revealed small, low-density lesions scattered throughout the spleen, consistent with splenic infarcts.

Diagnosis
Three sets of positive blood cultures from admission and another set of cultures from the second day identified N. elongata (Table 1).Antibiotics were tailored to ceftriaxone 2 g intravenously every 24 h.

Treatment
The patient underwent urgent repeat aortic and mitral valve replacement surgery.Intra-operatively, he was found to have vegetations on both prosthetic valves, which required extensive debridement.

Outcome
The post-operative course was complicated by congestive heart failure, cardiac tamponade, shock, respiratory failure and coagulopathy.The mitral and aortic valve surgical tissue Gram stain showed moderate white blood cells and no organisms.Surgical cultures were negative.
Based on the sensitivity results from the initial culture, the patient completed a 6-week course of ceftriaxone 2 g intravenously every 24 h.This treatment was compatible with previously described cases in the literature.Prior cases were treated with third-generation cephalosporin, benzylpenicillin or ampicillin/amoxicillin.Ceftriaxone is more convenient to administer than ampicillin or benzylpenicillin given its once-daily dosing requirement.Trans-thoracic echocardiogram prior to discharge revealed normal heart function with normal-appearing prosthetic mitral and aortic valves.

Discussion
N. elongata, first described in 1970, is an aerobic, Gramnegative coccobacillus within the family Neisseriaceae.The organism can occasionally be Gram-variable.It is considered to be a commensal of the human oropharynx, and is closely related to Kingella, Eikenella and Moraxella species, and Centers for Disease Control group EF4 (Hoshino et al., 2005;Noheria et al., 2010).N. elongata is a rare, but increasingly recognized cause of infective endocarditis.The species N. elongata includes three subspecies: N. elongata subsp.elongata, N. elongata subsp.glycolytica and N. elongata subsp.nitroreducens (formerly Centers for Disease Control group M-6).Various systemic infections have been reported, such as septicaemia, endocarditis and osteomyelitis.N. elongata subsp.nitroreducens has been most frequently linked to infective endocarditis (Hsiao et al., 2008;Noheria et al., 2010).
Risk factors include pre-existing valvular heart disease, preceding dental work, history of rheumatic heart disease and a prior history of endocarditis.The typical presentation is an acute, febrile, destructive endocarditis with large vegetations, often with systemic complications, such as congestive heart failure, perivalvular abscess (30 %), renal failure (30 %) or embolic phenomena (Struillou et al., 1993;Hsiao et al., 2008).
A review of the literature, including this case, revealed 24 cases of N. elongata endocarditis (Table 2).The reported age range was 7-82 years, with a mean of 49 years.All reported cases, including ours, involved the aortic or mitral valve (Hsiao et al., 2008;Noheria et al., 2010).Of the 24 cases, 15 met the diagnosis of definite infectious endocarditis according to the modified Duke criteria and nine met criteria for possible endocarditis.Eight of the 24 cases (33 %) were in patients with prosthetic valves.
To the best of our knowledge, this is the first reported case of N. elongata endocarditis involving both prosthetic mitral and aortic valves.The bivalvular involvement made surgical treatment more challenging as more extensive debridement had to be done to control the source of infection.Surgical treatment for multivalve endocarditis is associated with higher morbidity and mortality (Ota et al., 2011).
N. elongata is susceptible to a wide range of antimicrobial agents, with variable susceptibility to penicillin.All cases were treated with a third-generation cephalosporin, benzylpenicillin or ampicillin/amoxicillin, usually combined with gentamicin the initial phase.Duration of antibiotic therapy was usually 4-6 weeks (Struillou et al., 1993;Hoshino et al., 2005).Surgical valve replacement was required in 12 (50 %) of the 24 patients (Hsiao et al., 2008;Noheria et al., 2010).
N. elongata is an uncommon, but increasingly recognized, cause of infective endocarditis.It causes severe valvular destruction with systemic complications and often requires surgical intervention.

Fig. 1 .
Fig. 1.TEE of the mitral valve vegetation in three dimensions.