what was the name of the organism found in patient 64538 last sputum microbiology test in 03/2100.
select microbiologyevents.org_name from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 64538 ) and microbiologyevents.spec_type_desc = 'sputum' and microbiologyevents.org_name is not null and strftime('%y-%m',microbiologyevents.charttime) = '2100-03' order by microbiologyevents.charttime desc limit 1