the present invention relates to a selectively purified tanshinone compounds containing extract from the root of a salvia spp comprising cryptotanshinone , dihydrotanshinone , tanshinone i , and tanshinone iia . it comprises at least 15 %, by weight of the said identified tanshinone compounds and at least 4 % by weight , of cryptotanshinone . the extract and formulations thereof have been found to exhibit excellent anti - microbial properties against , in particular mrsa .