It is nearly always possible to find some fungus or bacteria that will grow on a particular organic substrate. Organic building materials are seldom subject to by-product attack, but almost all are susceptible to attack for the remaining reasons listed under Reasons for Biological Attack. This is particularly true if a material blocks a pathway to food. In the marine environment, inert materials usually become objects of attachment. The actual mechanisms of microbial attack are little understood and even today there is not much basic research in this field.
Most work is empirical, designed only to obtain a quick answer to an immediate problem.
In general, it can be said that bacteria and fungi act at the molecular level. Their secretions break chemical bonds and degrade the molecules to fractions that can be assimilated by the organisms. Most secretions are solutions of enzymes and even when the secreting organism has died the enzymes may continue to function. With animals, digestion of food usually occurs within the organism. The primary attack is physical at the structural level of the material, i.e., gnawing or boring.