This study analyzed the microbiome in thrombi, arterial blood, and venous blood samples obtained from patients with acute ischemic stroke. The results revealed that several bacterial taxa, including Bacillus, Corynebacterium, Parabacteroides, Romboutsia, Roseburia, Prevotella, and Streptococcus, exhibited a higher relative abundance in thrombi compared to arterial blood samples. Our findings may suggest a distinct microbial profile within the thrombus compared to the circulating arterial blood.
A wide range of infectious agents have been associated with the development of atherosclerosis (16, 17). Streptococcus mitis, commonly found in the oral cavity, can enter blood flow, adhere to vascular endothelium, induce platelet aggregation, and then form a biofilm that may serve as attachment points for other bacteria (18). Periodontitis, caused by Gram-negative bacteria, can lead to persistent endotoxemia (19, 20). It is worth noting that endotoxemia is quite common after periodontal examination, tooth extractions, and even tooth brushing (21, 22). The gut, which has the greatest variety and number of bacteria in the human body (23), is considered a significant source of endotoxins (24). Bacteria can enter the bloodstream and reach atherosclerotic plaques through compromised intestinal epithelial membranes or macrophage phagocytosis (25). Studies have demonstrated the presence of oral and gut bacteria in valvular vegetation, endocardium, and atherosclerotic plaques (8, 13, 26). These findings indicate the potential involvement of both oral and gut bacteria in the pathogenesis of atherosclerosis.
Accumulating evidence suggests that bacterial infection can accelerate the rupture of atherosclerotic plaque (9, 27). The debris resulting from these plaque ruptures can then obstruct downstream arteries, potentially leading to cerebral infarction. When a plaque ruptures, the microorganisms contained within it can enter the in-situ thrombus (12). Additionally, specific species such as Bacillus cereus and Bacillus anthracis have been found to have the ability to directly initiate blood coagulation and enter the thrombus (28). These mechanisms further emphasize the potential role of bacterial infections in promoting thrombus formation and its subsequent complications.
Left atrial remodeling plays a significant role in the development of atrial fibrillation (AF) and stroke. One of the key features of left atrial remodeling is the dilation and dysfunction of the left atrium, which can result in blood stasis within the atrial chambers (29). This stagnant blood flow provides an ideal milieu for bacteria to aggregate and potentially initiate infections. Bacterial interactions with platelet receptors are of particular importance in the context of thrombosis. Bacteria or bacterial-derived factors, such as lipopolysaccharide, can bind to platelet receptors, leading to platelet activation. This activation can further trigger neutrophil engagement and the release of neutrophil extracellular traps, all of which contribute to the promotion of blood coagulation (30). Moreover, bacterial DNA has been shown to have heparin-like properties. This bacterial DNA can form antigenic complexes similar to those formed with heparin, resulting in comparable levels of platelet aggregation and thrombosis (31). This highlights the potential role of bacterial DNA in promoting thrombotic events.
This study established an association between alcohol consumption and the bacterial burden observed in cerebral artery thrombi. Previous research has linked alcohol drinking to the advancement of atherosclerosis (32). Long-term alcohol consumption has been shown to alter the composition of the intestinal microbiota and compromise the integrity of the intestinal mucosal barrier (33). Consequently, the increased intestinal permeability may facilitate the entry of pathogens into the bloodstream (34, 35). Heavy alcohol consumption has been specifically associated with an elevated cardiovascular risk within the subsequent day (36). These findings suggest that the detrimental effects of alcohol consumption on the intestinal microbiota and mucosal barrier may contribute to an increased bacterial burden in cerebral artery thrombi.
Our study acknowledged a major limitation regarding the 16S rRNA gene sequencing method employed, which only allowed for the detection of bacterial DNA within the samples but not the live microorganisms or their metabolic activity. The small size of the samples hindered the quantification of bacterial DNA concentration within the thrombi. Additionally, there is a possibility that the observed excessive relative abundance of certain genera within the thrombi could be attributed to phagocytized bacterial components derived from biofilms. These limitations underscore the need for future studies to explore the functional aspects of bacterial involvement in thrombogenesis, beyond mere DNA detection, and to investigate the specific roles played by bacterial components in the process.
The detection of bacterial signatures typically found in the oral cavity and digestive tract within thrombi from patients with ischemic stroke suggests a potential role for bacterial infection in thrombogenesis and an increased risk of ischemic stroke. This finding supports the idea that bacteria present in these regions may contribute to the development of thrombi and subsequent stroke. Moreover, long-term alcohol consumption has been associated with an increased risk of ischemic stroke. This suggests that alcohol drinking may further enhance the risk of bacterial infection-associated thrombogenesis and ischemic stroke. These observations highlight the potential interplay between bacterial infection, thrombogenesis, and the increased risk of ischemic stroke. Further research is needed to better understand the underlying mechanisms and develop effective preventive measures and treatments.