tell me the name of the organism found in the last blood culture microbiology test on patient 15968 in 08/2100?
select microbiologyevents.org_name from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 15968 ) and microbiologyevents.spec_type_desc = 'blood culture' and microbiologyevents.org_name is not null and strftime('%y-%m',microbiologyevents.charttime) = '2100-08' order by microbiologyevents.charttime desc limit 1