what was the organism found in the last mini-bal microbiology test for patient 3369 until 04/2103?
select microbiologyevents.org_name from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 3369 ) and microbiologyevents.spec_type_desc = 'mini-bal' and microbiologyevents.org_name is not null and strftime('%y-%m',microbiologyevents.charttime) <= '2103-04' order by microbiologyevents.charttime desc limit 1