A decrease in the ability of a pathogen (like a virus or disease-causing bacteria) to cause disease.
The ability of a bacterium to regulate the amount of an amino acid it makes based on how much is already present, whereby excess amounts of the amino acid will turn off symthesis of itself.
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.