| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
|
© 2004 European Association of Cardio-Thoracic Surgery
Polymerase chain reaction diagnosis in culture-negative prosthetic valve methicillin-resistant Staphylococcus aureus endocarditis in a patient with chronic liver disease
a Department of Cardiothoracic Surgery, Western Infirmary, Glasgow, UK
* Corresponding author. Address: Garden Flat, 184 Nithsdale Road, Pollokshields, Glasgow G41 5EU, Glasgow, UK. Tel.: +44-797-4932-614; fax: +44-141-211-4845 Received August 23, 2003; received in revised form November 14, 2003; accepted November 24, 2003
We report the use of polymerase chain reaction for the diagnosis of prosthetic valve methicillin-resistant Staphylococcus aureus endocarditis in a patient with chronic liver disease where conventional laboratory testing failed. This case highlights the diagnostic and therapeutic potential of molecular techniques in the management of culture-negative endocarditis.
Key Words: Prosthetic valve endocarditis; Methicillin-resistant Staphylococcus aureus; Polymerase chain reaction; Chronic liver disease; Culture-negative
Prosthetic valve endocarditis (PVE) is a serious condition with high early and late mortality irrespective of the treatment employed and its frequency is increasing ranging from 0.1 to 2.3% per patient year [1–3]. Its outcome is determined by the disease itself and individual patient characteristics. Patients with cirrhosis have an increased susceptibility to bacterial infections. Endocarditis may complicate cirrhosis, typically involving the mitral valve, with Staphylococcus aureus the most likely pathogen [4]. Despite the development of new culture methods and improved media to aid the detection of previously non-culturable or fastidious microorganisms, culture-negative endocarditis occurs in up to a quarter of all cases often resulting in delayed diagnosis and increased morbidity. In this respect the culture-independent, molecular amplification technique of polymerase chain reaction (PCR) has been shown to offer a more specific and rapid alternative [5–8].
A 56-year-old male with primary biliary cirrhosis was referred to our centre for routine mitral valve replacement (MVR) and closure of atrial septal defect (ASD) in October 2002. A screening medical in 1993 led to the detection of moderate mitral incompetence secondary to anterior leaflet prolapse. Although asymptomatic, regular follow-up revealed gradual left atrio-ventricular dilatation with associated atrial fibrillation and pulmonary hypertension necessitating his referral. On admission transthoracic echocardiography (TTE) confirmed severe mitral regurgitation, small ASD and normal left ventricular function. MVR with a Sorin Bicarbon mechanical prosthesis and repair of the ASD were performed on October 25, 2002. The post-operative course was complicated by a pneumothorax which resolved spontaneously. He was discharged home on the 7th post-operative day. Two weeks after surgery the patient was readmitted with a 2-day history of tense sternal wound pain and fever. Physical examination revealed erythema with serous discharge over the distal 2–3 cm of the sternal wound. Bacteriology confirmed methicillin-resistant Staphylococcus aureus (MRSA) in both blood and wound swab cultures. Despite appropriate antibiotic therapy with vancomycin and gentamicin he continued to spike temperatures. As repeated infection screens and an Indium-111 leucocyte scintigraphy scan were all negative, both antibiotics were stopped on day 32 of readmission. TTE on days 2, 10 and 18 and transoesophageal echo (TOE) on day 25 of readmission were reported as normal. He was discharged home again on day 37, apyrexial. Four days later, 8 weeks post-MVR, he was readmitted for the second time with general malaise, uncontrolled atrial fibrillation and hypotension. Over the following 24 h, he developed acute left ventricular failure. TOE showed severe para-prosthetic mitral regurgitation with lateral aspect dehiscence, moderate global reduction in contractility and evidence of vegetations. The right atrium and ventricle were dilated with moderate tricuspid regurgitation. Blood cultures were taken prior to recommencement of vancomycin and gentamicin therapy. An intra-aortic balloon pump was inserted ahead of emergency MVR with another Sorin valve. Multiple blood cultures taken pre- and post-operatively, intra-operative tissue from the sternum, screening swabs and the excised prosthetic valve were all culture-negative. Considering the clinical history, vancomycin and gentamicin therapy was continued. PCR assay of the excised valve ensued and confirmed the diagnosis of MRSA PVE. His post-operative course thereafter was uncomplicated. He continued on the combined antibiotic therapy of vancomycin and gentamicin for 3 weeks after redo-surgery. The gentamicin was then stopped and he was transferred to the referring hospital for completion of a further 3 weeks of vancomycin therapy. 2.1. Molecular testing Excised prosthetic valvular tissue was investigated at the Scottish MRSA Reference Laboratory using a multiplex PCR assay that identifies the four major SCCmec types (I, III and combined II/IV) with primers designed by Dr Neil Woodford [9]. A DNA preparatory method (NucleoSpin®) was incorporated initially to improve sensitivity and concentrate the organism in the clinical specimens. Prepared samples were amplified according to reference laboratory protocol and products separated by agarose gel electrophoresis (Fig. 1 was transferred). Both mecA positive and negative controls were included throughout. Gels were stained with ethidium bromide and viewed under UV light.
The clinical diagnosis of infective endocarditis is generally difficult. This is often exacerbated in culture-negative cases where previous antibiotic therapy or the presence of fastidious organisms results in an inability to culture the causal agent. Various guidelines have been proposed to aid the diagnosis and the most reliable of these to date, the Duke Criteria, has recently incorporated molecular analysis into the newest revision acknowledging its increased diagnostic sensitivity in culture-negative cases [10]. PCR is a culture-independent, molecular amplification technique designed to detect specified genes in tiny quantities of microorganisms. The method is able to correctly identify the mecA gene in Staphylococcus aureus which confers methicillin resistance [9]. Direct detection of the mecA gene using this methodology produces rapid and reliable results that surpasses phenotypic methods and could potentially improve the management of patients with MRSA. Specificity of the antibiotic treatment can also be improved by including the investigation of common antimicrobial resistance genes into the molecular approach [5,6,9]. In the above report conventional laboratory testing identified MRSA from initial blood cultures but failed to detect MRSA from cultures thereafter, including tissue removed from the patient peri-operatively. The excised margins of the valve received in the laboratory were friable, with visible vegetations in this region and on the leaflets. PCR produced bands corresponding to mecA and staphylococcal nuclease from valve tissue on two occasions, inferring that the tissue harboured MRSA. This confirmed clinical suspicion and allowed continued targeted antibiotic treatment. In conclusion, this case demonstrates how the use of a molecular technique in patients with culture-negative PVE can increase diagnostic sensitivity and therapeutic specificity to improve patient outcome.
We are grateful to Michael Coyne and other biomedical scientists at the Department of Microbiology, Western Infirmary Glasgow, for their excellent technical assistance and to Dr Donald Morrison, Scottish MRSA Reference Laboratory, for allowing us access to the laboratory and methods. Funding was made available by the Scottish Centre for Infection and Environmental Health (SCIEH). doi:10.1016/j.icvts.2003.11.008
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN | EUR J CARDIOTHORAC SURG |
| J THORAC CARDIOVASC SURG | ICVTS | ALL CTSNet JOURNALS |
Top
Abstract
1. Introduction