The ability of a diverse range of bacterial species to infect atherosclerotic tissue has been well Raclopride documented. However, it has been proposed that atherosclerotic tissue may act as a ��mechanical sieve�� trapping bacteria present in blood circulation and that detected bacteria, although present, may have no pathological significance. In contrast, our study was confined to the adventitia and was from areas of minimal macroscopic signs of atherosclerosis. The current study supports the hypothesis that bacterial infection may contribute to the pathophysiology of atherosclerosis. The bacteria IC 87201 identified included an array of environmental and oral species. Most of these species have previously been reported as opportunistic or nosocomial pathogens. For example, members of the Stenotrophomonas genus, which were detected in both RA+CVD and CVD patients, have recently emerged as important opportunistic pathogens in debilitated individuals, and have been reported to infect immunocompromised individuals with increasing frequency. Stenotrophomonas maltophilia has been demonstrated to cause blood-stream infections. Furthermore, several species of Stenotrophomonas including S. maltophilia, express a protease capable of breaking down fibrinogen, fibronectin and collagen, which could cause local tissue damage and as such may be a potential atherogenic trigger. M. oryzae was detected in the adventitia of all three 16S rRNA gene-positive RA+CVD patients, and may act as a primary pathogen. However, eight samples did not appear to harbour bacterial DNA. This could be due to bacteria being present at a level below that detectable by the standard PCR detection method used. It could be also be possible that bacteria contributed to disease pathology at a time prior to sampling. The occurrence of M. oryzae in vessels may occur in a patchy pattern and differs in segments of the vascular tree, thus it is possible that we did not detect all cases with M. oryzae in the aorta since we examined only a small aortic specimen and not the whole aorta. Alternatively, the pathology in these eight non-infected samples could be driven by other unknown mechanisms. Interestingly, Methylobacterium sp. has previously been identified in human aortic aneurysm samples. Although knowledge of M. oryzae is lacking, insight may be gained from considering its closest known relative, M. mesophilicum. Interestingly, M. mesophilicum has been reported as a cause of opportunistic infections in immunocompromised hosts and has been isolated from several clinical sites, including blood, synovial, and cerebral spinal fluid.