100% ETOH is alleged to dehydrate, delipidize, and denature the superficial
layers of the cells to form a permeation barrier, limiting or at least
slowing killing. 70% apparently diffuses in farther, disrupting
lipo-proteins and killing more efficiently. For disinfecting surfaces,
a mixture of hypochlorite and detergent is often used, though for flaming
spreaders, loops, etc. 70% ETOH is usual. BTW, ascospores of Neurospora
crassa can survive this treatment occasionally.