Amensalism is a relationship in which a product of one organism has a negative effect on another organism.[4] It is specifically a population interaction in which one organism is harmed, while the other is neither affected nor benefited. Usually this occurs when one organism exudes a chemical compound as part of its normal metabolism that is detrimental to another organism. The bread mold penicillium is a common example; penicillium secrete penicillin, a chemical that kills bacteria. A second example is the black walnut tree (Juglans nigra), which secrete juglone, a chemical that harms or kills some species of neighboring plants. This interaction may nevertheless increase the fitness of the non-harmed organism by removing competition and allowing it greater access to scarce resources. In this sense the impeded organism can be said to be negatively affected by the other's very existence, making it a +/- interaction. A third example is when sheep or cattle make trails by trampling on grass, thereby destroying a food source. Examples of bacterial interference: Bacterial interference can inhibit growth. For example, attine ants (which belong to a New World tribe) are able to take advantage of an amensalistic relationship between an actinomycete and the parasitic fungi Escovopsis. These ants cultivate a garden of a different fungal species, Leucocoprini, for their own nouri

hment. They also promote the growth of an actinomycete of the genus Pseudonocardia s., which produce an antimicrobial compound which inhibits the growth of Escovopsis, which would otherwise decimate their store of Leucocoprini.[5] The bread mold Penicillium secretes penicillin, a chemical which kills bacteria. New findings demonstrate another mechanism of bacterial interference called interspecific molecule synergy. This discovery is based on the evidence that there are molecules of different species which have a synergistic relationship and exert a bactericidal effect on a third species which neither has when acting independently. An example of this mechanism is the effects of the protein epiP, which is secreted by inhibitory strains of S. epidermidis which impair the formation of biofilms by S. aureus and can even destroy S. aureus biofilms. When working alone, however, the protein epiP has no bactericidal effect against S. aureus. But in synergy with hBD2 (human beta-defensin 2), a protein present in the human immune system, the two proteins working together kill S. aureus. S. aureus resides in the nasal cavities of many humans from where it can cause severe inflammation that can lead to diseases such as pneumonia, endocarditic and septicemia. Thanks to this cooperation mechanism between S. epidermidis and humans, the development of such disease can be counteracted.