Endocarditis of Native Valve due to Proteus mirabilis: Case Report and Literature Review

Design

Case presentation

An 86-year-old female with a history of aortic arch replacement and atrial fibrillation presented with fever, dysuria, and altered mental status and was found to have sepsis secondary to ciprofloxacin-resistant, ESBL-negative Proteus mirabilis bacteremia with concomitant urinary tract infection and bilateral non-obstructive nephrolithiasis. Initial laboratory evaluation demonstrated leukocytosis, acute kidney injury, and elevated C-reactive protein.

Following an equivocal transthoracic echocardiogram, transesophageal echocardiography revealed a 12-mm mobile vegetation attached to the anterior mitral valve leaflet with moderate mitral regurgitation, fulfilling modified Duke criteria for definite native mitral valve infective endocarditis. She was managed medically without valve replacement, initially with intravenous ceftazidime plus renally adjusted gentamicin.

During the first week of therapy, she developed acute visual loss attributed to branch retinal artery occlusion from an embolic event. Surveillance blood cultures became negative after 1 week, and repeat transesophageal echocardiography after 2 weeks showed reduction in vegetation size, prompting discontinuation of gentamicin and continuation of beta-lactam therapy.

After 4 weeks of inpatient antimicrobial therapy, she was discharged on ertapenem for an additional 4 weeks. At completion of 8 total weeks of therapy, transesophageal echocardiography demonstrated resolution of the vegetation, with improvement in renal function and inflammatory markers.

Study Author Conclusions

Native endocarditis due to Proteus is rare. The major risk factor appears to be urinary tract infections with the concomitant presence of nephrolithiasis. The embolic events are not rare. The optimal antimicrobial treatment, the duration of treatment, and the association with surgery are unknown. The patients who underwent surgery have done a shorter antibiotic therapy. However, most patients were treated only with medical therapy with a good cure rate and the only two cases that died were reported in literature on 1973 and 1977. The clinical cases reported in literature are the only guide for the clinicians, but are a few sample size to assess for an association between the type of antimicrobial treatment regimen administered or whether surgery was performed and outcome; so it is more important to report the clinical case in order to provide an increase in sample size.

Rare case of Proteus mirabilis native mitral valve endocarditis in an immunocompromised patient

Design

Case presentation

A 65-year-old female with rheumatoid arthritis treated with chronic prednisone and tofacitinib, factor V Leiden hypercoagulability, and prior saddle pulmonary embolism presented after a mechanical fall with generalized fatigue and was found to have evolving sepsis secondary to pan-susceptible Proteus mirabilis complicated urinary tract infection associated with a 4-mm ureteral stone.

Computed tomography demonstrated acute/subacute splenic emboli, and transthoracic echocardiography revealed native mitral valve infective endocarditis with a large mobile vegetation on the anterior mitral leaflet measuring 1.2 × 0.5 cm and associated moderate mitral regurgitation. Initial broad-spectrum therapy with piperacillin/tazobactam was narrowed after blood and urine cultures grew P. mirabilis susceptible to ceftriaxone and gentamicin; treatment was changed to ceftriaxone 2 g intravenously every 24 hours plus gentamicin 5 mg/kg/day divided every 8 hours.

Despite combination therapy, the patient developed persistent bacteremia, acute pulmonary edema, new-onset atrial fibrillation with rapid ventricular response, and mixed septic and cardiogenic shock requiring intensive care, noninvasive ventilatory support, inotropes, and multiple vasopressors. Repeat echocardiography showed progression to a larger nonmobile mitral vegetation measuring 1.1 × 0.8 cm with severe mitral regurgitation and pulmonary venous flow reversal.

After ureteral stent placement, she underwent mitral valve replacement on hospital day 7, with valve pathology confirming acute infective endocarditis and P. mirabilis isolated from the surgically removed valve. Following surgery, blood cultures cleared, vasoactive and inotropic support were discontinued, gentamicin was stopped, and ceftriaxone monotherapy was continued for 6 weeks after the procedure; the patient was discharged home on postoperative day 5.

This case therefore describes initial ceftriaxone-plus-aminoglycoside therapy during persistent bacteremia and clinical deterioration, followed by source control and valve replacement with successful completion of prolonged ceftriaxone monotherapy after surgery.

Study Author Conclusions

We hypothesize that the patient’s immunocompromised status following steroid and Janus Kinase inhibitor usage for rheumatoid arthritis contributed to Gram-negative bacteremia following P. mirabilis UTI, ultimately seeding the native MV. Additional studies with larger numbers of Proteus endocarditis cases are needed to investigate an association between immunosuppression and Proteus species endocarditis.

Proteus Kills: A Rare Case of Mitral Valve Infective Endocarditis from Proteus Mirabilis Bacteremia

Design

Case presentation

A 57-year-old man with end-stage renal disease on hemodialysis presented with one day of chills and was found to have hypotension, tachycardia, leukocytosis, and recent outpatient blood cultures positive for pan-susceptible Proteus mirabilis, with ceftriaxone minimum inhibitory concentrations within the susceptible range. The presumed source was a femoral tunneled hemodialysis catheter, which was exchanged over a guidewire because a complete catheter holiday was limited by multiple stenotic vessels.

He was initially treated with ceftriaxone, then briefly broadened to vancomycin and piperacillin-tazobactam during clinical deterioration with suspected septic shock, before being narrowed back to ceftriaxone after subsequent blood cultures were negative. His course was complicated by embolic neurologic events involving the bilateral cerebral hemispheres, left cerebellum, and lower pons, and transesophageal echocardiography demonstrated a large 1.4 × 1.5 cm vegetation on the anterior mitral valve leaflet with leaflet perforation.

Cardiothoracic surgery deemed him a high-risk operative candidate, and medical management was continued. Despite ceftriaxone therapy and apparent microbiologic clearance, he developed persistent leukocytosis and progressive mixed septic and cardiogenic shock, ultimately complicated by cardiac arrest and death after transition to comfort-focused care.

This clinical outcome contrasts with prior reported experience in Proteus mirabilis endocarditis in which ceftriaxone plus gentamicin, selected on the basis of in vitro time-kill synergy testing, achieved bactericidal activity and clinical cure, suggesting that ceftriaxone monotherapy may be insufficient in selected cases of high-burden disease such as mitral valve endocarditis with large vegetation, embolic complications, inadequate source control, or inability to pursue surgical intervention.

Study Author Conclusions

Given its high mortality compared to other causes of IE, Proteus IE could benefit from standardization of in vitro time-kill studies to identify antimicrobial regimens which would provide the highest chances of cure.

Successfully Treated Mitral Valve Proteus mirabilis Endocarditisrence Number

Design

Case presentation

A 64-year-old man with no significant prior medical history presented with 11 days of fever, chills, exertional dyspnea, cough, and several weeks of urinary frequency and urgency.

On admission, he was febrile and tachycardic, with bibasilar rales, an apical holosystolic murmur, mild pulmonary venous congestion, leukocytosis, and urinalysis showing pyuria and hematuria. Two admission blood cultures grew Proteus mirabilis susceptible to ampicillin, ceftriaxone, trimethoprim-sulfamethoxazole, and gentamicin.

Transthoracic echocardiography demonstrated a mobile anterior mitral leaflet mass with mitral regurgitation, and transesophageal echocardiography confirmed a large 2.5-cm² mobile vegetation on the anterior mitral valve leaflet with moderate-to-severe mitral regurgitation, meeting revised Duke criteria for definite infective endocarditis.

The patient was treated with intravenous ceftriaxone 2 g daily without adjunctive aminoglycoside therapy; subsequent blood cultures remained negative, but repeat transesophageal echocardiography after approximately 3 weeks showed persistent vegetation size and regurgitant severity with limited clinical improvement.

He underwent bioprosthetic mitral valve replacement on hospital day 22, with pathology showing acute valvulitis and a 2 × 1.5 cm vegetation; valve tissue cultures were negative after prolonged antibiotic exposure. His postoperative course was uncomplicated, and at 3-month follow-up he remained clinically well without evidence of recurrent infection or heart failure.

This case therefore describes successful survival of native mitral valve P. mirabilis endocarditis with large vegetation using prolonged ceftriaxone-based therapy plus surgical valve replacement, but it does not provide direct comparative outcome data for ceftriaxone alone versus ceftriaxone combined with an aminoglycoside.

Study Author Conclusions

Infective endocarditis due to P mirabilis remains rare and is usually fatal. Echocardiographic evaluation is particularly important in establishing the diagnosis because Proteus bacteremia is relatively common in the absence of endocarditis. Despite the high fatality rate associated with this infection, our case illustrates that Proteus endocarditis can be successfully treated with intensive antibiotics and surgical intervention.

Proteus Mirabilis: A Rare Cause of Infectious Endocarditis

Design

Case presentation

A 58-year-old female with a history of mitral stenosis presented with a 2- to 3-week history of fever, night sweats, malaise, constitutional weight loss, and visual symptoms, and was found to have Proteus mirabilis bacteremia in association with bacteriuria and renal calculi.

Evaluation demonstrated leukocytosis, elevated inflammatory markers, and a superotemporal branch retinal artery occlusion consistent with an embolic phenomenon. Given persistent Gram-negative bacteremia and concern for infective endocarditis, transesophageal echocardiography was performed and revealed a highly mobile vegetation measuring 6 × 8 × 11 mm attached to the posterior leaflet of the native mitral valve. Blood and urine cultures grew pan-sensitive P. mirabilis.

The patient was treated with a 4-week course of intravenous ceftriaxone without adjunctive aminoglycoside therapy. Although blood cultures remained positive for 4 days after admission, she had prompt defervescence and symptomatic improvement after initiation of antimicrobial therapy, with subsequent clearance of bacteremia and no recurrent embolic events, valvular destruction, or perivalvular complications. Surgical intervention was not pursued.

Follow-up transesophageal echocardiography 2 months later demonstrated regression of the mitral valve vegetation, and blood cultures remained negative. At 12-month follow-up, she remained clinically well with normalization of laboratory parameters and no evidence of relapse.

This case therefore supports a favorable outcome with ceftriaxone monotherapy in susceptible P. mirabilis native mitral valve endocarditis with a relatively small vegetation, while prior reported cases with larger vegetations were more commonly associated with valve replacement or death, limiting direct comparison with ceftriaxone plus aminoglycoside therapy.

Study Author Conclusions

Proteus mirabilis endocarditis remains a rarely reported entity. We attribute early imaging studies and aggressive intervention with appropriate antibiotics in susceptible patients, along with favorable vegetation size, position, and regression to be the most important factors in contributing to a non-surgical outcome in this patient.