Consecutive patients diagnosed with acute ischaemic stroke during hospitalization in Prince of Wales Hospital will be recruited.

After an informed consent, stool will be collected from enrolled patients in their first bowel opening after hospitalization and stored in a freezer (-80 degree Celsius) within 24 hours for analysis. If a subject develops constipation, stool sampling will be facilitated by stool softener or laxatives. Stools samples will be stored at -80 degrees Celsius within 24 hours once it is collected.

Subjects will be followed up at 3 and 6 months after trial entry. NIHSS and mRS will be performed at each visit. Stool sample collection will be repeated in 6 months visit only.

Age and disease matched subjects will be invited to join the study as the control. Stool will also be collected for the comparison of gut microbiota with acute stroke patients to look for evidence of gut dysbiosis in acute stroke. We shall match the control cohort with the stroke cohort in terms of age, gender, smoking status, medical co-morbidities including hypertension, hyperlipidaemia, diabetes, (atrial fibrillation), use of medications in particular metformin, proton pump inhibitors and aspirin.

Gene sequencing of the 16S rRNA on the stool samples are performed to identify the microbes down to genus level, as well as the microbrobiota diversity and relative abundance. And stroke etiology classified by TOAST Classification and disability indices (NIHSS & mRS at baseline, 3 month & 6 month) will be recorded.

Gene sequencing of the 16S rRNA on the stool samples are performed to identify the microbes down to genus level, as well as the microbrobiota diversity and relative abundance. All patients who received a plain CT brain & MRI for the diagnosis of stroke will be reviewed. Infarct volume in DWI, MR angiography abnormalities, presence of microbleed and/or haemorrhagic transformation will be documented.