"The biblical plague of the Philistines now has a name, tularemia."
"The laboratory isolation of F. tularensis requires special media such as buffered charcoal yeast extract agar. It cannot be isolated in the routine culture media because of the need for sulfhydryl group donors (such as cysteine)." - Wiki
Thus a cysteine deficiency or chronic low cysteine would be expected to make this disease worse, the bacterium gets it first, the immune systems gets what's left over. Which wasn't enough in the first place. Death follows.