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A case of Bartonella henselae native valve endocarditis presenting with crescentic glomerulonephritis

Bartonella endocarditis is often an elusive diagnosis, usually derived from evaluating multiple laboratory tests and assessment of presenting symptoms. Herein we describe a case of Bartonella henselae native mitral valve endocarditis with an initial presentation of volume overload and renal failure. The Bartonella organism is tedious to isolate from culture medium, causing most diagnoses to be delayed. Due to the destructive nature of B. henselae endocarditis, the need for rapid identification remains prudent. This therefore creates an opportunity for Next Generation Sequencing (NGS) to be used. We further summarize the varied presentations that may be associated with B. henselae endocarditis, and hope that this will heighten the clinicians’ awareness of this entity when presented with acute onset renal failure and culture negative vegetations.


Introduction
From the flea's stomach to the human heart, Bartonella henselae remains elusive in its abilities and characteristics, rising in the ranks as one of the most common causes of culture negative endocarditis. They are fastidious, facultatively intracellular and pleomorphic gram-negative bacilli with the ability to evade culture detection and produce biofilms. The two species that predominantly stand out for causing culture negative endocarditis are B. henselae and B. quintana. Bartonella's slow growing behavior and requirement for heme create a difficult environment for culture detection. Herein, we will describe a case of Bartonella endocarditis complicated by crescentic glomerulonephritis. We will review the pathogenesis of these infections, alternate presentations, diagnostic modalities and the currently available therapies.

Case report
65-year-old Caucasian male with a medical history significant for bicuspid aortic valve, childhood aortic valve procedure (patient was unable to clarify, but no prosthetic material) and first-degree heart block, who presented with progressive shortness of breath over a two month period. He had acute worsening two to three days prior to admission with a twenty-minute episode of chest pain day of admission. He recorded a 100.1 F temperature at home with chills. Other past medical history was notable for hyperlipidemia, prior stroke with residual right-sided deficit, 48-pack-year tobacco history, and a social history significant for both indoor and outdoor pets consisting of cats, dogs and birds. Vital signs at admission temperature 100.1 F, blood pressure 136/67, pulse 87, and oxygen saturation 99% on room air. Physical exam with bibasilar crackles with faint expiratory wheezing. A II/VI systolic crescendo-decrescendo murmur with radiation to the carotids was noted on auscultation with minimal lower extremity edema. Labs were remarkable for a white blood cell count of 4600 /uL, hemoglobin 9 g/dL, platelets 117,00 /uL, creatinine 1.95 mg/dL, normal liver function tests. SARS-CoV-2 RNA and influenza screens were negative. He was started on empiric pneumonia treatment with vancomycin, ceftriaxone and azithromycin. On hospital day 2, a transthoracic echocardiogram revealed mild to moderate mitral regurgitation with a mobile density of the anterior leaflet concerning for a vegetation. The aortic valve was not visualized well. One set of blood cultures was collected prior to antimicrobial initiation, eventually returning negative. That evening he developed acute tachycardia, hypotension and hypoxia. CT of the chest was obtained revealing peripheral ground-glass infiltrates with "crazy paving." He underwent a bronchoscopy with negative studies. Infectious disease was consulted on hospital day 3 for multifocal pneumonia as well as mitral valve findings. Blood cultures were obtained and were negative. Plasma Next Generation Sequencing testing available on day 8 with 9653 DNA molecules per microliter (MPM) of Bartonella henselae detected. Given concern for Bartonella endocarditis, on hospital day 8 antimicrobials were changed to doxycycline and rifampin. Bartonella quintana and Bartonella henselae IgG testing positive with reflex titers of 1:512 and > / = 1:1024, respectively, and Brucella IgG positive at 3.02, all three available on day 9 (Table 1). Nephrology was consulted on day 5 secondary to progression of renal failure with creatinine rising to 2.13 mg/dL (prior normal creatinine). Given his pulmonary symptoms, autoimmune testing was completed on day 5 for anti-GMA, ANCA, and ANA negative, C3 and C4 borderline low at 80 mg/dL and 17 mg/dL, respectively. On day 9, renal biopsy was performed which showed focal necrotizing and crescentic glomerulonephritis. His renal function progressively worsened, but he remained non-oliguric. Renal dosed gentamicin was added to his therapy in place of rifampin on hospital day 17 after discussions with nephrology. That same day, he underwent a mitral valve replacement with intraoperative TEE noting stenotic mitral valve with central regurgitation, anterior and posterior leaflet thickening, and a bicuspid aortic valve with mild to moderate stenosis. Both mitral leaflets were excised, with the valve sent for pathology noting chronic inflammation, negative for fungal and bacterial organisms, as well as culture which was negative. Unfortunately, 16s rRNA sequencing from the valve was requested but not sent. Postoperative course was complicated by worsening renal failure requiring hemodialysis and hemorrhage requiring sternal exploration and washout. Gentamicin was discontinued after 14 days of therapy to assist with renal recovery. The patient remained on doxycycline 100 mg BID planned for 6 weeks of treatment post valve replacement. Unfortunately, he suffered a sudden PEA arrest, and expired on hospital day 34.

Discussion
Bartonella species are fastidious, intracellular, gram-negative organisms that reside within erythrocytes. Due to this unique predilection, Bartonella is known to inhabit two specific sites: the gut of bloodsucking arthropods and bloodstreams of mammalian hosts [1]. Cats have been identified as hosts when they become infected with B. henselae following the bite of infected fleas. Bartonella is transmitted to humans from a scratch (salivary contamination through grooming) or a bite from an infected cat. We reviewed 17 case reports from 2010 and 2020, 14 of those cases had contact with cats ( Table 2).
Bartonella is a problematic organism to isolate from culture media. Blood cultures have as low as a 20% sensitivity [2]. Direct plating of blood or tissue is preferred with specialized agars (heart infusion, Trypticase soy, brucella agar, and Columbia agar supplemented with 5% hemoglobin) and incubated for up to 21 days. Special staining such as Warthin-Starry can be used but these are not specific for Bartonella. Serology seems to be the most informative. B.
henselae IgG titers > 1:800 are considered to have the greatest sensitivity for endocarditis with positive predictive value of 0.955 [3]. Low level titers could indicate prior exposure to the bacteria or cross reactivity. IgM assays have lower sensitivity rates since assays react early in the disease process and wane after 10 weeks, but higher specificity than IgG [3]. False positive results may occur with Coxiella burnetii and Chlamydophila pneumoniae. PCR testing has been utilized on both serum and tissue with serum sensitivity is 33% and tissue sensitivity is 92% [4]. 16s rRNA from tissue is considered the gold standard, but is invasive. 16s rRNA requires the use of primers that are limited to a certain portion of the genome and thus do not always provide accurate results [5]. Usually, the diagnosis of bartonellosis involves several methods to corroborate the results.
Next Generation Sequencing (NGS) of microbial cell free DNA (mcfDNA) is a new and emerging diagnostic test. This method is noninvasive with a short turnaround time (28 h), detecting the normal products of bacterial turnover within the body. When we compare the turnaround time to serology, NGS and IFA are almost equal, adding in two to four days for NGS specimen shipping. As the test becomes more readily available, this should improve. The NGS test relies on sequencing mcfDNA in circulating plasma to identify over 1000 pathogens (including bacteria, fungi, viruses) and reports a quantitative amount as molecules per microliter (MPM). In one study, NGS reported a 95% sensitivity in culture positive endocarditis even with antimicrobial pre-treatment [3]. NGS was ordered for our patient given the expected low yield from routine blood cultures and to capture other fastidious organisms. From reflection of our case, the differential diagnoses were initially broad, therefore using NGS and IFA together helped secure a diagnosis. We used both tests to advocate for prompt surgical intervention. The downfalls to NGS are that it may pick up on low yield microbiota/viroma, requiring clinical interpretation [6] and average NGS costs are roughly twenty times more expensive than IFA. During literature review, it was noted that in some cases patients were left on doxycycline until IFA titers decreased. Serial NGS testing could be considered to evaluate pathogen levels and monitor responses, as down-trending MPM levels correlate directly with decreasing amounts of viable pathogen [7]. This topic however, needs further investigation and would prove to be useful especially since serial IgG levels overtime have been inconsistent [8].
Bartonella is the leading cause of culture negative endocarditis in the US [9] and second most common CNE pathogen worldwide [4]. The species typically infects native valves with the aortic valve being the most commonly reported [4]. Prosthetic valve infections have been described, with clinical presentations that are usually severe with rapid progression to heart failure. Rarely, cases of myocarditis associated with B. henselae and B.quintana infections have been reported. Some reports resulting in sudden unexpected cardiac death in previously healthy individuals [2]. About 70% of patients require valve replacement secondary to severity of valve damage [10]. Mortality remains low at 7% [10]. Various reviews of pathology found histologic findings such as fibrosis, endothelial proliferation and neovascular formation that were distinctive to Bartonella [11][12][13]. The suggestion is for higher calcification and less extensive vegetation material, indicating a more chronic inflammatory process [12]. These findings are supportive of the need for surgical intervention in addition to antimicrobials for clearance rather than medical management alone.
Renal failure is a common manifestation of Bartonella endocarditis, with one study estimating greater than 40% of patients present with such findings [14]. Specifically, rapidly progressive renal failure is noted to be a clinical feature in infection-associated glomerulonephritis (GN). Serology testing is typically done to rule out an autoimmune diagnosis in these instances; however, renal biopsy to assess for histological patterns appears to be of vital diagnostic value. Severe damage to the glomerular capillary walls results in crescent formation, findings that can be seen with immune   complex diseases such as postinfectious GN, lupus nephritis, IgA nephropathy and vasculitis, as well as anti-glomerular basement membrane disease and antineutrophil cytoplasmic antibody (ANCA) vasculitis [15]. Interestingly, there is evidence of ANCA positivity in serum for many Bartonella endocarditis patients, with one review demonstrating 77% of cases with these findings [16]. Furthermore, a 2014 case report and literature review of Bartonella endocarditis cases reported that 50% of the eight reviewed cases were c-ANCA positive [4]. The correlation between CGN and Bartonella endocarditis may be one where, in settings of unexplained renal failure and concordant findings on biopsy, the diagnosis of Bartonella should be considered.
To further assess this correlation, we reviewed 17 case reports between 2010 and 2020 ( Table 2). These cases were selected based on diagnosis of infectious glomerulonephritis via renal biopsy and/or an extensive autoimmune work up. In 7 of the 17 cases the patient underwent renal biopsy, revealing features characteristic of crescentic glomerulonephritis, with treatment of Bartonella resulting in restoration of renal function. Concurrent infectious and auto-immune work up was completed in 10 cases given symptoms and negative blood cultures.
In axenic media, Bartonella species appear to be susceptible to many antimicrobials, including penicillin, cephalosporins, fluoroquinolones, macrolides and aminoglycosides, but the correlation between in vivo and in vitro is lacking [17]. Gentamicin is the aminoglycoside that appears to be most studied [18]. There appear to be limited or no prospective studies to support treatment guidelines for endocarditis, and most recommendations are largely based on retrospective, observational data. Many experts recommend dual therapy for effective treatment, at least in the initial 2 weeks [18]. The AHA (2005 edition) recommends using doxycycline for 6 weeks after valve surgery or 12 weeks total if the valve is retained and gentamicin for at least 14 days. Alternatives to doxycycline are macrolides with recommendation for 12 weeks minimum with valve surgery and 6 months without surgery. Valve replacement seems to be central to appropriate therapy, having occurred in 80% of past cases [17]. If gentamicin cannot be used, notably in settings where renal function is a concern, the alternative is rifampin for at least 14 days. Gentamicin is chosen because aminoglycosides are bactericidal, and doxycycline has been shown to penetrate erythrocytes. The combination works well to eradicate the bacteria in different niches within the host [18,19]. In a retrospective study of 101 patients, at least 14 days of aminoglycosides (in combination with another antimicrobial) demonstrated higher rates of recovery as compared to non-aminoglycoside monotherapy [20]. The question remains whether bactericidal activity is required for clearance of the organism. Some data shows Bartonella residing within erythrocytes may afford protection from gentamicin, hence the recommendation to use more than one agent [19]. Interestingly, there is in vitro data to support the use of azithromycin/ciprofloxacin and rifampin/ciprofloxacin combinations to completely eradicate biofilms after 6 days and kill stationary phase Bartonella after day 1 of exposure [21]. The total duration of antimicrobial treatment is not clearly defined, leaving room for future guidelines to assist with clarification.

Conclusion
Bartonella endocarditis remains difficult to identify and manage. Several concurrent presenting symptoms may lead the clinician towards this diagnosis, including renal failure with an auto-immune-like component. NGS may have an up-and-coming role in both diagnosis and treatment. Treatment remains largely surgical, with improved outcomes seen with the use of combination antimicrobial therapy.

Ethical approval
Not applicable-no studies conducted on the patient.

Consent
Not applicable-no studies conducted on the patient/no patient identifying information used in the case report.

Funding
There are no funding sources to declare.

Author contribution
Roshni Patel, Kansas Koran and Amanda Schnee contributed composition and construction of the work. Mark Call assisted with critical edits.

Disclosure
No conflict of interest to disclose for all authors. Our case report does not include factors necessitating patient consent.