when did patient 25103 since 05/2103 first receive the stool microbiology test?
select microbiologyevents.charttime from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 25103 ) and microbiologyevents.spec_type_desc = 'stool' and strftime('%y-%m',microbiologyevents.charttime) >= '2103-05' order by microbiologyevents.charttime asc limit 1