what was the name of the organism found in patient 24894's first blood culture (post-mortem) test, which took place in their last hospital encounter?
select microbiologyevents.org_name from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 24894 and admissions.dischtime is not null order by admissions.admittime desc limit 1 ) and microbiologyevents.spec_type_desc = 'blood culture (post-mortem)' and microbiologyevents.org_name is not null order by microbiologyevents.charttime asc limit 1