BACKGROUND AND OBJECTIVES: Chronic periodontal bacterial infections and disruptions in gut microbiota are responsible for systemic inflammation, which may contribute to the rupture of intracranial aneurysm. This study aimed to assess the presence of bacterial DNA from Fusobacterium nucleatum and Escherichia coli within arterial tissues of intracranial aneurysms. METHODOLOGY: A comprehensive cross-sectional study was conducted, applying stringent inclusion and exclusion criteria to carefully select the study population from patients admitted to the Division of Neurosurgery at Hospital das Clínicas, University of São Paulo. Samples were collected post-aneurysm microsurgical clipping, preserving their integrity for subsequent DNA extraction. Polymerase chain reaction (PCR) techniques were employed to identify bacterial DNA within these samples. RESULTS: In total, 36 patient samples underwent a detailed analysis. The presence of Escherichia coli DNA exhibited a statistically significant correlation with the occurrence of ruptured intracranial aneurysms (Qualitative Odds Ratio [OR] 4.3 [1.01 - 23.4] and Quantitative OR 0.99 [0.99-1.0], Student's t-test [P = 0.9]). However, the presence of Fusobacterium nucleatum DNA did not demonstrate a statistically significant correlation with ruptured intracranial aneurysms (Qualitative OR 1.52 [0.4-6.1] and Quantitative OR 0.04 [0.01-5.22 ×108], Student's t-test [P = 0.78]). CONCLUSION: The identification of Escherichia coli bacterial DNA in arterial tissues was positively associated with the occurrence of ruptured intracranial aneurysms, suggesting a potential role for these microorganisms in aneurysm pathogenesis and rupture. The development of therapeutic and prophylactic strategies can be established through future research endeavors.