So here it is...
Ampicillin HELPS to clear Enterococci!
Ps: Gram-negative organisms have 'porin' channels in their outer lipid membrane through which the Beta-lactam antibiotics enter the cell. Also the lipopolysaccharide layer that contains endotoxins! (Gram-positive organisms do not have such things in their cell wall)
The only exception is Listeria monocytogenes that has little amounts of such endotoxins, inspite of being Gram-positive bacteria!