As a Home Inspector my advice is as follows.... The mold or fungus is there because there is water/ moisture in the crawlspace. The mold and or fungus can not live without water. First you have to find the cause of the moisture and correct that problem. Is it ground water, leaky pipe, exterior rain water entering the area what ever, you have to cure that water problem. IF not any clean up will be useless and the issue will return. Next a complete covering of the ground with a thick plastic is needed from wall to wall. No gaps. Is there a way for any water that enters later ...leaky pipe.... to exit the crawlspace. Floor drain or sump pump. Proper ventilation is a must.... Many people today are sealing their crawlspaces and making them conditioned spaces to prevent problems. Still not sure about this not enough time gone by to see if this really works. There are many companies that will do the work need to cure the problem. As an Inspector if i came to inspect this home and found it had new plastic and clean and dry surroundings there would be no issue to report to the client. Not all inspectors are residential mold certified and their insurance companies will not let them talk about mold for that reason. Hope this helps.