when did patient 2425 on the first hospital encounter receive stool microbiology test for the last time?
select microbiologyevents.charttime from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 2425 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and microbiologyevents.spec_type_desc = 'stool' order by microbiologyevents.charttime desc limit 1