Echocardiographic diagnosis of an aortic root abscess after Mycobacterium fortuitum prosthetic valve endocarditis

Prosthetic Valve Infective Endocarditis With Mycobacterium Fortuitum: Antibiotics Alone Can Be Curative

Rapidly growing non-tuberculous mycobacteria (RGM) are a rare, often fatal cause of infective endocarditis. Although surgery has been the cornerstone of RGM endocarditis therapy, we present the first documented adult case of Mycobacterium fortuitum endocarditis cured with antibiotic therapy.

Sternal wound infection caused by Mycobacterium chelonae

INTRODUCTION

Sternal wound infection caused by Mycobacterium chelonae, a member of the rapidly growing nontuberculous mycobacteria (NTM), is rare and may present without signs and symptoms of systemic infection.

METHODS

We present a patient who had a M. chelonae infection of the sternum following excision of a left atrial myxoma and conducted a review of the literature from 1976 to 2013.

RESULTS

Seventy cases of NTM sternal wound infection after cardiac surgery were identified, including six outbreaks and ten sporadic cases including the present case. Thirty-four cases were isolated coronary artery bypass grafting (CABG) surgery, 16 cases were isolated valve replacement, and two cases were valve replacement with CABG. The age range of the patients was between 6 and 78 years. The average time from the surgery was 49 ± 58 days which was longer than the usual bacterial mediastinitis. The overall mortality rate was 29%.

CONCLUSION

NTM sternal wound infection is rare but may be fatal if not properly treated. The toxic signs are often subtle and it will take longer to isolate compared to typical bacterial mediastinitis. Early recognition, the use of appropriate antibiotics based on susceptibility tests, and aggressive surgical debridement are required for full recovery.

Mycobacterium fortuitum prosthetic valve endocarditis: a case for the pathogenetic role of biofilms

BACKGROUND

Prosthetic valve endocarditis presents unique challenges for both diagnosis and treatment. A potential role of biofilm has been hypothesized in the pathogenesis of these infections.

METHODS

A patient with infective endocarditis involving a stentless (Freestyle) porcine prosthetic aortic valve with annular abscess and paravalvular leak 8 months after implantation is reported.

RESULTS

The infected valve did not show vegetations or perforations, but histiocytic inflammation was seen along the endocardial surfaces of the valve. Auramine-rhodamine staining revealed many acid-fast organisms associated with the inflammation. There was also an acellular matrix material with ultrastructural features of biofilm. Blood cultures grew Mycobacterium fortuitum, a biofilm-associated microbe.

CONCLUSIONS

The role of biofilm in prosthetic valve endocarditis is discussed. The importance of microscopy for prosthetic valves, even when no vegetations are present, is highlighted along with correlation of pathologic findings with culture results.

Mycobacterial prosthetic valve endocarditis

Prosthetic valve endocarditis (PVE) due to mycobacteria is a rare but frequently fatal complication that may occur early after the surgical procedure, or even years later. Infection has been described with both mechanical and biologic valvular prosthesis. The most commonly implicated mycobacterial species belong to the rapid-grower group (M. chelonei, M. fortuitum, and M. abscessus) of nontuberculous mycobacteria (NTM). The source of infection in this context is thought to be nosocomial, likely related to preoperative or intraoperative contamination of the prosthesis by contact with aqueous solutions containing the organisms. These infections are difficult to diagnose because blood cultures are often negative. Clinically, it is important to recognize the possibility of NTM-PVE in the differential diagnosis of culture-negative patients who develop signs and symptoms of endocarditis, whether they present early or late in onset after the surgical procedure. These patients should be treated with surgical removal of the infected valve, followed by adequate antimicrobial therapy based on the susceptibility of the species isolated from the valve or perivalvular tissue culture. In a significant number of patients, however, an unstable hemodynamic condition ensues, precluding surgical intervention, and therefore leading to a high mortality rate.

Mycobacterium fortuitum complex endocarditis-case report and literature review

Endocarditis due to Mycobacterium fortuitum complex is a rare entity generally linked to the hospital environment. Only 18 cases have been published since 1966. Here we present a case of a female who developed an endocarditis due to Mycobacterium chelonae after valve replacement as well as a review of the literature. The course of this kind of endocarditis is generally subacute and the outcome is usually fatal. Blood cultures were positive in 75% of cases of metallic valve endocarditis, versus 20% in bioprostheses. The treatment must include antibiotics that have shown activity against these mycobacteria, such as amikacin, imipenem, cefoxitin, fluorinated quinolones and macrolides (especially clarithromycin). Surgical removal is recommended. Although the prognosis for the patient is poor, we should expect better outcomes with the use of new antibiotic regimens.

Endocarditis due to rare and fastidious bacteria

The etiologic diagnosis of infective endocarditis is easily made in the presence of continuous bacteremia with gram-positive cocci. However, the blood culture may contain a bacterium rarely associated with endocarditis, such as Lactobacillus spp., Klebsiella spp., or nontoxigenic Corynebacterium, Salmonella, Gemella, Campylobacter, Aeromonas, Yersinia, Nocardia, Pasteurella, Listeria, or Erysipelothrix spp., that requires further investigation to establish the relationship with endocarditis, or the blood culture may be uninformative despite a supportive clinical evaluation. In the latter case, the etiologic agents are either fastidious extracellular or intracellular bacteria. Fastidious extracellular bacteria such as Abiotrophia, HACEK group bacteria, Clostridium, Brucella, Legionella, Mycobacterium, and Bartonella spp. need supplemented media, prolonged incubation time, and special culture conditions. Intracellular bacteria such as Coxiella burnetii cannot be isolated routinely. The two most prevalent etiologic agents of culture-negative endocarditis are C. burnetti and Bartonella spp. Their diagnosis is usually carried out serologically. A systemic pathologic examination of excised heart valves including periodic acid-Schiff (PAS) staining and molecular methods has allowed the identification of Whipple's bacillus endocarditis. Pathologic examination of the valve using special staining, such as Warthin-Starry, Gimenez, and PAS, and broad-spectrum PCR should be performed systematically when no etiologic diagnosis is evident through routine laboratory evaluation.