Septicemia caused by cysteine-dependent Escherichia coli

A case of septicemia and urinary tract infection caused by cysteine-dependent Escherichia coli in a 70-year-old woman with bilateral staghorn calculi is described. This is the second report of a cysteine-dependent E. coli bacteremia. The bacterium was falsely susceptible to ampicillin and co-trimoxazole when tested on a medium without cysteine supplement.