As the immortal bard once wrote: "To crush or not to crush, that is the question. Whether tis more antifungal to crush the clove or leave it whole ..."
Well the active (antifungal and antibacterial) ingredient of garlic is allicin.
Allicin does not occur in garlic naturally. Instead, garlic cloves contain the amino acid alliin (S-allylcysteine sulphoxide):
Structure of Alliin
When garlic is crushed or otherwise damaged, the alliin reacts with the enzyme allinase, also found naturally in garlic. Allinase acts as a catalyst and results in the transformation of alliin into allicin (diallyl thiosulphinate):