what organism has been found in the first mini-bal exam of patient 31854 during this hospital encounter?
select microbiologyevents.org_name from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 31854 and admissions.dischtime is null ) and microbiologyevents.spec_type_desc = 'mini-bal' and microbiologyevents.org_name is not null order by microbiologyevents.charttime asc limit 1