16S PCR in patients with an infected vascular graft, mycotic aneurysm or a non-infected aortic aneurysm

A vascular prosthesis infection is a rare, but very serious complication. This
complication implies an extensive reoperation with explantation of the graft
and revision wit an autologous (venous) graft. This therapy requires major
surgery and is associated with 15% mortality, even in experienced hands.
Postoperatively, patients are treated with antibiotics for at least 6 weeks. A
primary infection of an artery, often presenting as a mycotic aneurysm, is
treated rather similarly. The infected arterial wall will be excised
completely, followed by a reconstruction using antilogous vein or an
antibiotic-impregnated vascular prosthesis. In these patients additional
treatment with 6 weeks of antibiotic therapy postoperatively is indicated too.
Long-term antibiotic therapy is intended to prevent recurrent vascular
prosthesis infection or a potentially lethal septic bleeding from a venous
graft. The type of antibiotic therapy for patients with an infected arterial
wall or vascular prosthesis is determined by the type of bacterium causing the
infection. Therefore, identification of bacteria from the infected arterial
wall or vascular prosthesis is important and typing of a bacterium is obtained
by means of microbacterial cultures. The sensitivity for this test in these
patients may be limited and in 25% of patients no bacteria will be
demonstrated. There is a need for a better test to demonstrate the presence of
bacteria in the arterial wall and vascular prostheses. Molecular techniques to
demonstrate the presence of bacteria may have additional diagnostic value in
these patients.

16S PCR

The 16S PCR is a molecular technique to demonstrate and identify bacteria. The
16S rRNA gene is necessary to bacterial protein synthesis and is present in all
bacteria. Using specific parts of the 16S rRNA gene most culturable and
non-culturable bacteria can be identified. Using 16S PCR the bacterial 16S rRNA
base sequence can be determined. The bacterial identity is then determined by
comparing the base sequence with the sequences of already identified bacteria.
The 16Spatch database, for example, contains the sequences of more than 1.000
unique bacteria.

Bacteria in the arterial wall

Since 1999 the 16S PCR technique has been used in multiple publications to
demonstrate the presence of bacteria atherosclerotic plaques. This technique
has always been used in research projects studying the pathogenesis of
atherosclerosis. However, prior to the use of 16S PCR, it has been known that
bacteria may be present in atherosclerotic arteries of patient without symptoms
of a bacterial infection. In a series of 176 patients, who underwent open
aortic aneurysm repair using a vascular prosthesis, positive mural thrombus
cultures were observed in 14% of patients. During follow up however, no graft
infections were registered. In another series of 500 patients undergoing aortic
aneurysm repair bacteria in the arterial wall were demonstrated in as many as
185 patients (37%). One patient developed a prosthetic graft infection after 6
years caused by a bacterium other than the one found during the initial
operation. The authors therefore conclude, that routinely culturing
asymptomatic, non-ruptured aneurysms is not indicated, since a positive culture
has no consequences.

The aim of this study is to compare the 16S PCR technique with standard
bacterial cultures of infected vascular grafts, mycotic aneurysms and
non-infected aortic aneurysms.

Pilot study. In all patient undergoing surgery for an infected vascular graft,
mycotic aneurysm or non-infected aortic aneurysm tissue will be obtained to be
analysed by standard bacterial cultures and the 16S PCR test. If pus is found,
this will be analysed too. De 16S PCR results will be compared with the
standard bacterial cultures. The patients with non-infected aortic aneurysms
with negative bacterial cultures will be considered negative controles.

No burden and minimal risk.