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Ann Thorac Surg 2005;79:e21-e22
© 2005 The Society of Thoracic Surgeons
a Department of Cardiothoracic and Vascular Surgery, Friedrich-Schiller University Jena, Jena, Germany
b Institute of Medical Microbiology, Friedrich-Schiller University Jena, Jena, Germany
Accepted for publication February 10, 2004.
* Address reprint requests to Dr Madershahian, Department of Cardiothoracic and Vascular Surgery, Friedrich-Schiller University Jena, Bachstrasse 18, 07743 Jena, Germany
navid.madershahian{at}med.uni-jena.de
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Abstract |
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Introduction |
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Molecular techniques such as polymerase chain reaction (PCR) amplification and sequence analysis of the amplified DNA have been demonstrated to be a very useful tool for the detection and identification of noncultivatable agents of endocarditis [3, 4].
We report a case of culture-negative severe IE in a 17-year-old boy in which the etiologic diagnosis could only be provided by PCR amplification and sequencing of the bacterial 16S rRNA gene from valve tissue generating sequences for Streptococcus viridans.
A 17-year-old boy with severe IE and a small persisting ventricular septal defect since childhood was admitted to our department for further evaluation and consideration of surgical treatment. This followed a 3-month history of diarrhea, fever, and chills. Due to syncope, the patient was admitted to an outlying hospital. Transthoracic echocardiographic studies (M-mode, B-mode, and color-flow Doppler) revealed severe aortic regurgitation. It also showed multiple vegetations on the aortic and both surfaces of the anterior and posterior mitral leaflets. In addition, an aortic right shunt was diagnosed together with tricuspid regurgitation. The patient was started empirically on ceftriaxone and gentamicin and was transferred for further care.
At the time of transfer, the patient had a rectal temperature of 38°C. His heart rate was 116 beats per minute, blood pressure was 115/25 mm Hg, and respiratory rate was 28 breaths per minute. A grade 3 systolic and diastolic murmur was audible. There was evidence of cardiac failure (New York Heart Association class III–-IV) with edema of the lower extremities; no rashes or other skin lesions were observed. His chest and abdomen were otherwise normal. No neurologic deficits were detected. There was no arthritis or meningism. Laboratory tests showed an elevated C-reactive protein level (81.4 mg/L; normal range, <5 mg/L) and an evaluated white blood cell count (22.6 Tpt/L). Additional laboratory studies included hemoglobin of 6.5 mmol/L, hematocrit of 0.34, and a platelet count of 150 Gpt/L. Repeat previous blood cultures were negative. Transesophageal echocardiography showed a bicuspid aortic valve with vegetation on the anterior leaflet with a severe transvalvular leak across the aortic valve. There was evidence of an aortic root abscess with perforation from the right coronary sinus to the right atrium and a visible left-to-right shunt. Tricuspid valve vegetation was observed. The mitral valve was found to have vegetation on the anterior leaflet. There was mild to moderate mitral regurgitation. Due to clinical evidence of pulmonary edema and worsening cardiovascular status, he was taken to the operating room. When operated on, the patient was found to have an aortic root abscess with perforation into the right atrium and nearly complete destruction of all leaflet tissue of the aortic valve. Perforations were noted in the aortic and mitral valve leaflets, with large attached vegetations.
After aggressive tissue debridement, the entire aortic root was reconstructed with a pericardial patch, and an aortic root replacement with a 28-mm cryopreserved aortic homograft was performed.
A mitral valve replacement with a 29-mm Sulzer Carbomedics prosthesis was performed due to multiple vegetations and perforations. After the ventricular septal defect was closed, bicuspidization of the tricuspid valve was done. The patient's postoperative course was uneventful, and he was extubated 1 day after the operation. The intravenous therapy of tazobactam and gentamicin was continued for 3 months after surgery. The patient was discharged in good condition after 22 days and made a full recovery.
The excised valves were sent for histopathologic and microbiological examinations. Histology revealed active IE (gram-positive cocci), whereas the results of blood cultures and cultures of the aortic valve vegetations and surrounding tissues remained negative. Molecular biological analysis of the tissues including DNA extraction, PCR amplification with the broad-range eubacterial primers, and sequencing of the bacterial 16S rRNA gene led to the final diagnosis and established the presence of ß-hemolytic S. viridans group A, C, or G.
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Comment |
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After surgery, culture of vegetations from the explanted valves is the diagnostic method of choice for the definite diagnosis of IE. It has been shown to be more efficient than blood culture in recovering the microorganisms in patients with culture-negative endocarditis. The lack of germ isolation may be caused by healed endocarditis, previous antibiotic treatment, and use of crystalloid cardioplegia, which may cause an osmotic shock to the bacteria still located in the vegetation.
Using traditional biochemical methods, we were not able to identify the bacterium to the species level. Molecular diagnosis of IE with PCR amplification and sequence analysis of the amplified DNA have been demonstrated to be a promising tool for the detection and identification of noncultivatable agents of endocarditis [3, 4]. Some authors claim that a positive molecular diagnosis of IE should be added to the Duke classification scheme as a major criterion [6]. Using this methodology, a number of new bacteria have been linked to known or previously unrecognized infectious diseases [7].
To identify the organisms, molecular analysis including DNA extraction, PCR, and sequencing of a portion of the 16S rRNA gene was performed. This method has been applied to both general culture-negative infections [8] and, more specifically, to endocarditis [4]. In a study by Gauduchon colleagues [3], PCR contributed to the etiologic diagnostic of IE in 20% of cases. Goldenberger and coworkers [4] used a similar molecular approach to study 18 cases of IE and also identified the causative agent in two cases in which conventional blood culture obtained negative results.
In conclusion, we recommend that PCR, which is rapid and sensitive and, with regard to the costs of empiric, broad-spectrum antibiotic treatment and the different diagnostic approaches, an inexpensive tool for the detection of bacteria in selected patients with blood culture–negative IE if culture methods fail. As an aid in the diagnosis of culture-negative infections in the clinical laboratory, this method will have a promising positive impact on patient care. This particular method is fundamental for determining postoperative antibiotic treatment without having previous positive blood or tissue cultures.
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