when was the first sputum microbiology test given to patient 12775 during the current hospital encounter?
select microbiologyevents.charttime from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 12775 and admissions.dischtime is null ) and microbiologyevents.spec_type_desc = 'sputum' order by microbiologyevents.charttime asc limit 1